KoritheMan's WunderBlog

Tropical weather analysis - August 27, 2014

By: KoritheMan, 7:59 AM GMT on August 27, 2014

Notice: All forecasts presented here are based upon my own knowledge of atmospheric dynamics. They are created using my knowledge of the various computer models, satellite interpretation, and other tools and parameters. These forecasts, while striving to be accurate, are not intended to supersede predictions by the National Hurricane Center. Always follow NWS protocol and forecasts.

Cristobal

Hurricane Cristobal continues to move northward across the western Atlantic to the west of Bermuda. As of the 0600Z NHC intermediate advisory, the following coordinates were posted on the storm:

Wind: 80 mph, with higher gusts
Location: 30.4°N 72.0°W
Movement: Stationary
Pressure: 983 mb
Category: 1 (Saffir-Simpson Hurricane Wind Scale)

Like its predecessor Bertha, Cristobal's appearance on satellite does not resemble a typical hurricane. The convection is limited to two adjoining bands in the northern semicircle, with the western band trying to wrap around the ragged eye. Having said all of that, Cristobal's structure appears to be on the rebound, and if the convection can wrap more fully around the center, some additional strengthening could occur. Upper-level outflow is restricted to the south, but this is surprisingly probably more creditable to abundant subsidence on the western side of a deep-layer ridge over the southern United States than strong southwesterly shear.



Figure 1. Latest infrared satellite image of Hurricane Cristobal. Image credit: NOAA's Satellite Services Division (SSD).

The GFS and ECMWF show the most favorable upper-level wind configuration developing in Cristobal's path during the next 24-36 hours, and any barotropic intensification that is going to occur will have to do so during that window. Beyond that time, Cristobal will cross a sharp sea surface temperature gradient, and southwesterly shear will be increasing ahead of a progressive but deep mid- to upper-level trough moving across Atlantic Canada. It is uncertain how strong Cristobal might remain subsequent to extratropical transition. Most of the global models do show some intensification as a baroclinic low, and if those forecasts are correct, Cristobal could carry hurricane-force winds even longer than I have indicated below. Beyond 72 hours, I am unable to give a forecast point due to the limitations of the map I use to create my track forecasts. Due to the uncertainty, I have indicated some slight weakening at 72 hours, but it is entirely possible that baroclinic processes could keep post-tropical Cristobal stronger.

Satellite data suggest that Cristobal has probably begun to move again, although the data indicates that the hurricane has moved to the left of the NHC forecast points from 3Z. Other than a small westward shift to accommodate for this turn, my forecast track remains pretty similar to the NHC forecast track up until I terminate it after 72 hours due to the limitation of the graph. Most of the global models show Cristobal moving near or over southern Iceland in five days as a strong extratropical cyclone.

The tropical storm watch for Bermuda is still up. Although it is likely that Cristobal will not produce sustained tropical storm force winds there, especially in light of the current westward short-term shift, the wind field is large enough -- partially enhanced by a steep pressure gradient with the subtropical ridge to the east -- that some gusts to 40 or 45 kt could be possible on some of the higher elevations there.

Intensity forecast

Initial 08/27 0600Z 30.4°N 72.0°W 70 kt 80 mph
12 hour 08/27 1800Z 32.5°N 71.5°W 70 kt 80 mph
24 hour 08/28 0600Z 35.0°N 69.0°W 75 kt 85 mph
36 hour 08/28 1800Z 38.2°N 63.2°W 75 kt 85 mph
48 hour 08/29 0600Z 42.3°N 54.8°W 70 kt 80 mph
72 hour 08/30 0600Z 47.3°N 45.1°W 65 kt 75 mph: extratropical

Track forecast



Figure 2. My forecast track for Cristobal.

NHC storm information

000
WTNT34 KNHC 270536
TCPAT4

BULLETIN
HURRICANE CRISTOBAL INTERMEDIATE ADVISORY NUMBER 14A
NWS NATIONAL HURRICANE CENTER MIAMI FL AL042014
200 AM EDT WED AUG 27 2014

...CRISTOBAL HESITATES BUT STILL EXPECTED TO PASS TO THE NORTHWEST
OF BERMUDA LATER TODAY...


SUMMARY OF 200 AM EDT...0600 UTC...INFORMATION
----------------------------------------------
LOCATION...30.4N 72.0W
ABOUT 445 MI...715 KM WSW OF BERMUDA
MAXIMUM SUSTAINED WINDS...80 MPH...130 KM/H
PRESENT MOVEMENT...STATIONARY
MINIMUM CENTRAL PRESSURE...983 MB...29.03 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY...

NONE.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* BERMUDA

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...IN THIS CASE IN THE NEXT 24 HOURS.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA...PLEASE MONITOR
PRODUCTS ISSUED BY YOUR NATIONAL METEOROLOGICAL SERVICE.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 200 AM EDT...0600 UTC...THE CENTER OF HURRICANE CRISTOBAL WAS
LOCATED NEAR BY AN AIR FORCE RECONNAISSANCE PLANE NEAR LATITUDE 30.4
NORTH...LONGITUDE 72.0 WEST. CRISTOBAL HAS BEEN MOVING LITTLE
DURING PAST COUPLE OF HOURS...BUT IS FORECAST TO RESUME A MOTION
TOWARD THE NORTH NEAR 15 MPH...24 KM/H LATER THIS MORNING. A TURN
TOWARD THE NORTH-NORTHEAST AND NORTHEAST WITH A GRADUAL INCREASE IN
FORWARD SPEED IS EXPECTED OVER THE NEXT 48 HOURS. ON THE FORECAST
TRACK...THE CENTER OF CRISTOBAL WILL PASS TO THE NORTHWEST OF
BERMUDA LATER TODAY.

MAXIMUM SUSTAINED WINDS REMAIN NEAR 80 MPH...130 KM/H...WITH
HIGHER GUSTS. SOME STRENGTHENING IS POSSIBLE DURING THE NEXT DAY OR
SO.

CRISTOBAL HAS A LARGE WIND FIELD. HURRICANE FORCE WINDS EXTEND
OUTWARD UP TO 60 MILES...95 KM...FROM THE CENTER...AND TROPICAL
STORM FORCE WINDS EXTEND OUTWARD UP TO 240 MILES...390 KM.

THE MINIMUM CENTRAL PRESSURE JUST REPORTED BY AN AIR FORCE
RECONNAISSANCE PLANE WAS 983 MB...29.03 INCHES.


HAZARDS AFFECTING LAND
----------------------
RAINFALL...CRISTOBAL IS EXPECTED TO PRODUCE ADDITIONAL RAINFALL
AMOUNTS OF 1 TO 2 INCHES OVER BERMUDA.

WIND...TROPICAL STORM CONDITIONS ARE POSSIBLE ON BERMUDA WEDNESDAY
AND WEDNESDAY NIGHT.

SURF...SWELLS GENERATED BY CRISTOBAL ARE AFFECTING BERMUDA AND
PORTIONS OF THE U.S. EAST COAST FROM CENTRAL FLORIDA NORTHWARD TO
NORTH CAROLINA...AND WILL SPREAD NORTHWARD ALONG THE U.S. EAST COAST
OVER THE NEXT FEW DAYS. THESE SWELLS ARE LIKELY TO CAUSE
LIFE-THREATENING SURF AND RIP CURRENT CONDITIONS. FOR MORE
INFORMATION...PLEASE CONSULT PRODUCTS FROM YOUR LOCAL WEATHER
OFFICE.


NEXT ADVISORY
-------------
NEXT COMPLETE ADVISORY...500 AM EDT.

$$
FORECASTER AVILA



Ex-97L

A tropical wave located several hundred miles east of the Lesser Antilles, previously designated "97L" before the NHC ceased running models on it, is moving westward. Satellite images show that this system is very disorganized. The GFS develops a tropical cyclone in the Bay of Campeche from the southern portion of this tropical wave in about a week, a solution that it has been consistent on for the last day or so. Even if that does happen, I suspect the northern portion will be too disorganized to take advantage of potentially more favorable environmental conditions farther west.

Probability of development in 48 hours: 0%

Probability of development in 120 hours: 10%



Gulf of Mexico disturbance

An area of disorganized cloudiness and a few showers south of the southwestern Louisiana coast is associated with a weak surface trough. The vorticity is weak, dry air is abundant, and there is southwesterly shear over a system that's moving west-southwest to southwest, a synoptic situation that is not conducive for development. The global models show this system moving into southern Texas or northern Mexico during the next day or so, and I do not anticipate tropical cyclone development in this area.

Probability of development in 48 hours: 0%

Probability of development in 120 hours: 0%



Marie

The once mighty Marie is now a shell of its former self. As of the 0300Z NHC advisory, the following information was posted on Marie:

Wind: 90 mph, with higher gusts
Location: 21.6°N 121.4°W
Movement: WNW at 14 mph
Pressure: 971 mb
Category: 1 (Saffir-Simpson Hurricane Wind Scale)

Satellite data show little change to Marie's cloud pattern. Deep convection remains fairly deep for a high latitude hurricane entering cold waters, although shower activity remains limited in the northern semicircle, likely because that portion of the cyclone circulation is already over 23 to 24C sea surface temperature. Upper-tropospheric outflow remains remarkably well-defined, suggesting that Marie remains embedded within an environment of weak vertical shear.



Figure 3. Latest infrared satellite image of Hurricane Marie. Image credit: NOAA's Satellite Services Division (SSD).

Although the shear is unlikely to increase much during the next few days, Marie will be moving over progressively cooler waters and into a dry airmass associated with those waters. A steady weakening is expected during the next five days, with Marie becoming a remnant low in about 48 hours; however, I note that it is possible this transition could conceivably occur sooner. Some of the guidance shows the circulation dissipating before day five, but I suspect the models that show this aren't giving quite enough credit to the large circulation of Marie; as seen with Lowell last week, such circulations can take an exceptionally long time to fully spin down, particularly in the absence of vertical shear.

Satellite fixes suggest that Marie is moving to the left of the 0300Z NHC forecast track, likely due to a westward extension of the Pacific subtropical ridge. The 6z TVCA model consensus has shifted westward to accommodate for short-term trends, and my forecast track follows suit. It remains well to the left of the GFS and ECMWF global models forecast since those models move Marie northward before turning it westward, a solution that seems unrealistic in light of the deep-layer ridge ahead of Marie, and also because the cyclone is going to spin down, making it less susceptible to abrupt poleward turns, especially at longer ranges.

Intensity forecast

Initial 08/27 0600Z 21.3°N 120.8°W 80 kt 90 mph
12 hour 08/27 1800Z 22.0°N 123.2°W 75 kt 85 mph
24 hour 08/28 0600Z 22.6°N 125.0°W 65 kt 75 mph
36 hour 08/28 1800Z 23.4°N 127.6°W 50 kt 60 mph
48 hour 08/29 0600Z 24.5°N 131.3°W 40 kt 45 mph: post-tropical/remnant low
72 hour 08/30 0600Z 28.2°N 134.6°W 30 kt 35 mph: post-tropical/remnant low
96 hour 08/31 0600Z 30.1°N 136.1°W 25 kt 30 mph: post-tropical/remnant low
120 hour 09/01 0600Z 30.2°N 137.1°W 20 kt 25 mph: post-tropical/remnant low

Track forecast



Figure 4. My forecast track for Marie.

2014 Atlantic hurricane season 2014 Pacific hurricane season Hurricane Cristobal Hurricane Marie

Updated: 7:59 AM GMT on August 27, 2014

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Tropical weather analysis - August 25, 2014

By: KoritheMan, 8:05 AM GMT on August 25, 2014

Notice: All forecasts presented here are based upon my own knowledge of atmospheric dynamics. They are created using my knowledge of the various computer models, satellite interpretation, and other tools and parameters. These forecasts, while striving to be accurate, are not intended to supersede predictions by the National Hurricane Center. Always follow NWS protocol and forecasts.

Cristobal

Tropical Storm Cristobal continues to meander near the southeastern Bahamas. As of the latest NHC intermediate advisory, the following information was posted on the cyclone:

Wind: 50 mph, with higher gusts
Location: 24.5°N 72.9°W
Movement: Stationary
Pressure: 998 mb

Cristobal is generating some very deep convection this evening over the western Atlantic and adjacent Bahama islands, which is likely producing some very heavy rain and winds to tropical storm force across the southeastern portion of the archipelago. A reconnaissance aircraft has been investigating Cristobal this morning; the highest reported surface wind speed from the SFMR instrument aboard the plane has been around 45 kt, and there were flight-level winds as high as 55 kt in the large convective band southeast of the center. The National Hurricane Center took this into account and bumped up the initial intensity to 45 kt at 6z. Since that time, deep convection has begun to consolidate around the center, with cloud tops as cold as -70C to -80C enveloping the cental gyre. There is a good equatorial outflow jet due to the more favorable upper wind environment in that area, but it remains poor to the north due to about 20 kt of northerly shear on the backside of the deep continental ridge over the eastern United States.



Figure 1. Latest infrared satellite image of Tropical Storm Cristobal. Image credit: NOAA's Satellite Services Division (SSD).

Data from the aircraft, along with satellite, scatterometer, and microwave data suggest that the center of Cristobal has reformed a bit to the south, closer to the deep convection in an environment of less shear; this is not uncommon of weak, sprawling systems struggling to establish an inner core. Since the center appears to be a little farther south, some more intensification could occur in the short-term than was predicted by the NHC at 0300Z given the more favorable environment where the center relocation occurred. Most of the guidance makes Cristobal a hurricane in a few days, and my forecast will follow suit. I was tempted to go a little higher than 70 kt given the expected acceleration of Cristobal in the mid-latitude westerlies at later times, and also due to possibly increased upper divergence ahead of a shortwave mid- to upper-level trough providing ascent, but I withheld given the uncertainties in the trough to cyclone interaction. Most of the global models show Cristobal interacting with a frontal zone near Atlantic Canada by day five, so extratropical status is shown by then. It should be noted that the guidance generally doesn't seem eager to kill off Cristobal too quickly during the post-tropical stage, and it is likely that the system will remain a strong gale center for several days subsequent to extratropical transition.

As previously mentioned, a slew of data this morning indicates that Cristobal's center has reformed to the south of what the 0300Z NHC position was. Looking into the crystal ball, I see that the models did not substantiate a center reformation, which will throw off the 6z model runs. It is uncertain what implications this will have on the track, but I suspect any changes will be near term ones, not longer term. Because of the center reformation and the global models' now erroneous initialization of the storm, my forecast is significantly to the west of the model consensus TVCN, and the National Hurricane Center, particularly during the first couple of days, showing an initial northwestward motion before turning the cyclone into the westerlies. It is also slower than the NHC and much of the guidance as a result. While it is highly unlikely Cristobal moves back west under the ridge and makes landfall along the United States coast, there is a nonzero chance of this happening if the cyclonicity over the western Atlantic continues to weaken; currently there is a surge of strung out moisture to the north of Cristobal which could serve as the impetus for cyclonicity, with a small upper low not far to the north of that, which could also enhance the large-scale cyclonicity in the area and pull Cristobal slowly northward. This is the solution of the global models, but while they appear to be handling the synoptic pattern rather nicely, I do not know if Cristobal will interact as strongly with the reinforced cyclonicity as that guidance suggests, since again, their initialization was faulty due to the center relocation. UW-CIMSS synoptic steering data and water vapor imagery show that a small weakness still remains to the north of the storm, but it appears to be closing, at least temporarily. If the ridge ends up stronger than forecast in the near-term, Cristobal could go even farther west than I have indicated below, possibly significantly so. Having said all of that, recurvature remains the most viable option by far, and I give it a 10% chance that Cristobal will reform far enough south or the ridge will close off enough to induce a westward motion toward the United States coast. A gradual turn toward the east-northeast will acceleration is forecast later in the period as the cyclone gets caught up in the circulation of a mid-latitude trough now over the upper midwest.

I am not confident in the short-term track forecast.

Intensity forecast

Initial 08/25 0600Z 24.5°N 72.9°W 45 kt 50 mph
12 hour 08/25 1800Z 24.7°N 73.2°W 45 kt 50 mph
24 hour 08/26 0600Z 25.0°N 73.3°W 50 kt 60 mph
36 hour 08/26 1800Z 25.3°N 73.5°W 55 kt 65 mph
48 hour 08/27 0600Z 26.1°N 73.9°W 60 kt 70 mph
72 hour 08/28 0600Z 32.2°N 70.8°W 70 kt 80 mph
96 hour 08/29 0600Z 37.9°N 67.9°W 70 kt 80 mph
120 hour 08/30 0600Z 42.4°N 52.0°W 60 kt 70 mph: extratropical

Track forecast



Figure 2. My forecast track for Cristobal.



Karina

Karina continues to wind down under high shear. As of the 0300Z NHC advisory, the following information was available on Karina:

Wind: 45 mph, with higher gusts
Location: 17.5°N 129.3°W
Movement: E at 9 mph
Pressure: 1002 mb

After losing all deep convection near 0z, there has been a regeneration of fairly cold convection about 30 miles to the west of the center, confined to that direction due to strong easterly shear associated with outflow from large Hurricane Marie, which is dominating much of the eastern Pacific at this time.



Figure 3. Latest infrared satellite image of Tropical Storm Karina. Image credit: NOAA's Satellite Services Division (SSD).

As long as Karina maintains some semblance of deep convection, regardless of how much it will undoubtedly pulsate, the cyclone will remain a tropical cyclone. However, water vapor and satellite data show the already strong shear giving way to even stronger shear as Karina moves counterclockwise around the larger circulation of Marie. Most of the guidance except for the ECMWF and HWRF show the circulation of Karina being absorbed into Marie in about 48 hours, and I have chosen to follow the guidance that assimilates the cyclone quicker.

Karina is following the NHC forecast track closely, and my own track is not significantly different from theirs due to lack of reasons to be. Karina is forecast to move steadily into the larger circulation of Maria, ultimately becoming entrained into the south side of the powerful hurricane in a day or two.

Intensity forecast

Initial 08/25 0300Z 17.5°N 129.3°W 40 kt 45 mph
12 hour 08/25 1200Z 17.4°N 128.6°W 30 kt 35 mph
24 hour 08/26 0000Z 17.3°N 127.7°W 25 kt 30 mph: post-tropical/remnant low
36 hour 08/26 1200Z 16.9°N 126.3°W 20 kt 25 mph: post-tropical/remnant low
48 hour 08/27 0000Z: absorbed by Marie

Track forecast



Figure 4. My forecast track for Karina.



Marie

After becoming a Category 5 earlier on Sunday, Marie has weakened, but only a little. As of the 0300Z NHC advisory, the following information was posted on the hurricane:

Wind: 150 mph, with higher gusts
Location: 16.6°N 112.8°W
Movement: WNW at 12 mph
Pressure: 927 mb
Category: 4 (Saffir-Simpson Hurricane Wind Scale)

Satellite images suggest little change to the cloud pattern of the powerful hurricane over the last several hours. The small eye was cloud-filled around 6z up until about 7z, but recent images indicate it has cleared out again. Satellite estimates suggest that the hurricane may be a little weaker now, however. Upper-tropospheric outflow remains well-defined and the water beneath the hurricane remains quite warm.



Figure 5. Latest infrared satellite image of Hurricane Marie. Image credit: NOAA's Satellite Services Division (SSD).

Marie likely peaked in intensity Sunday evening when it hit 140 kt, and the hurricane is likely to steadily decline from this point onward. While there has been little change to the eye or the central dense overcast, satellite and microwave data this morning shows that the deep convective band emanating to the south of the large hurricane is gradually wrapping cyclonically closer to the inner core/CDO area, which could possibly be a precursor to a concentric eyewall cycle. The eye has not contracted enough for me to believe that yet, however, and if such a process is in the cards, it will probably take another 12 to 18 hours to complete. Waters remain around 29 to 28C underneath the hurricane until about 36 hours, when they begin to cool. A faster rate of weakening is expected at that point, with remnant low status shown by day four when Marie moves over cold waters in the high latitudes of the Pacific. However, I suspect the large circulation of Marie, similar to Lowell a few days ago, will be slow to spin down, so I've decided to carry tropical storm force winds with it even as it loses its convection and becomes a remnant low in 96 hours.

Satellite fixes indicate that Marie has been smoothly following the track of the National Hurricane Center and the model consensus. Assuming there are no temporal wobbles due to complex mesoscale processes inside the eyewall, Marie should follow a fairly smooth path around a large subtropical ridge to the north from southwestern Mexico to off the Pacific United States coastline. The global models show a small break in the ridge as Marie enters high latitudes at days four and five, so I've shown a subtle poleward bend between 72 and 96 hours in order to reflect this. However, my forecast track remains to the left of the model consensus since Marie will be a weak system at those times.

Of note, Marie is the first Category 5 to form in the eastern north Pacific since Hurricane Celia of 2010.

Intensity forecast

Initial 08/25 0300Z 16.6°N 112.8°W 130 kt 150 mph
12 hour 08/25 1200Z 17.4°N 114.7°W 125 kt 145 mph
24 hour 08/26 0000Z 18.2°N 115.7°W 115 kt 135 mph
36 hour 08/26 1200Z 19.2°N 117.3°W 100 kt 115 mph
48 hour 08/27 0000Z 20.3°N 119.2°W 95 kt 110 mph
72 hour 08/28 0000Z 22.1°N 123.5°W 65 kt 75 mph
96 hour 08/29 0000Z 24.4°N 128.6°W 40 kt 45 mph: post-tropical/remnant low
120 hour 08/30 0000Z 28.3°N 133.7°W 30 kt 35 mph: post-tropical/remnant low

Track forecast



Figure 6. My forecast track for Marie.

2014 Atlantic hurricane season 2014 Pacific hurricane season Tropical Storm Cristobal Tropical Storm Karina Hurricane Marie

Updated: 9:01 AM GMT on August 25, 2014

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Tropical weather analysis - August 21, 2014

By: KoritheMan, 6:57 AM GMT on August 21, 2014

Notice: All forecasts presented here are based upon my own knowledge of atmospheric dynamics. They are created using my knowledge of the various computer models, satellite interpretation, and other tools and parameters. These forecasts, while striving to be accurate, are not intended to supersede predictions by the National Hurricane Center. Always follow NWS protocol and forecasts.

Invest 96L

A convectively active tropical wave located a few hundred miles east of the Windward Islands ("96L") is a threat to develop into a tropical depression over the next few days. The system is showing some mixed signals this evening. On one hand, a 0100Z ASCAT pass showed a reasonably well-defined surface circulation in association with the wave, and there have been periodic hints of banding features attempting to wrap around the tropical wave axis, signifying that the low is attempting to organize. However, cloud tops have warmed significantly over the last few hours, and the areal extent of deep convection has decreased as well; this is important since the diurnal convective maximum is fast approaching in that area of the ocean, which is when we should expect to see an increase in deep convection over the water. There have been occasional hints of arc clouds emanating westward from the low-level center during the past several hours, suggesting some systematic subsidence within the tropical wave. It is worth noting that we still haven't been able to garner a Dvorak classification for this system yet, indicating it still has a ways to go to become a tropical cyclone, particularly with the decrease in convection. There may also be a little bit of southeasterly shear afflicting the system due to the upper-level anticyclone being displaced a little to the northeast of the wave, which is fairly consistent with the the 0300Z CIMSS 850-200 mb averaged wind shear estimate.



Figure 1. Latest infrared satellite image of Invest 96L. Image credit: NOAA's Satellite Services Division (SSD).

Although the environment is currently only marginal as the MDR continues to be unfavorable this year, there are indications of decreasing upper-level winds in the path of the system in the eastern Caribbean Sea as denoted by analysis of water vapor imagery. The GFS and ECMWF show a large anticyclonic upper wind pattern developing over the system as it moves across the Caribbean Sea, a solution which is not impossible with current trends already indicating lower shear. One aspect of note is that 96L is a monsoonal system, and such systems typically take a long time to spin up, but they can also prove unusually resilient to large-scale environment hostilities like vertical shear and dry air entrainment. I don't expect much additional organization during the next day or so, and in fact I would not be surprised to see convection weaken significantly as we head into the diurnal minimum today. However, by the time the system reaches the eastern Caribbean Sea, it should have a chance to intensify under an environment of very light shear and perhaps a slightly more moist airmass. I still think the system will hold off on developing into a tropical cyclone until it gets west of 60W, and possibly even closer 65W assuming it doesn't run smack dub into Hispaniola, which much of the models are calling for.

The long-term track of the system is uncertain. It appeared to be moving more toward the northwest late Wednesday evening, but the motion has now stabilized to a more uniform west-northwest motion, toward the eastern Caribbean. Water vapor and UW-CIMSS synoptic steering data show a strong, westward-extending subtropical ridge nosing all the way to the Bahamas, but there is a small weakness in the western portion of the ridge between 70 and 80W which is keeping the ridge somewhat fragile in that area. This weakness appears to be symptomatic of an upper cold low embedded within the mid-oceanic trough. This low appears to be weakening, and at first it was a little puzzling to me why so many of the models were starting to insist on recurving 96L east of the United States in a pattern favoring strong ridging over the east coast with a fairly weak western Atlantic trough. I took the time to more closely examine the model fields, and the best I can make out is that a quasi-stationary upper low and trailing trough near Hudson Bay dives southeastward into the Atlantic over the next few days and reinforces the cyclonic flow in the area just as the upper low begins to die off. Since it is impossible for me to determine the depth and amplitude of a trough still over the US when the weakness is well south of it, the only I can really do is "nowcast", for lack of a better term; see if reality lines up with the various model progs. Right now the weakness is fairly small, and becomes less evident with height as you go down in the troposphere, so I am a little south of the 0z model suite, which takes the system near or over Puerto Rico and then across eastern Hispaniola. Assuming the situation doesn't change tomorrow in regards to the strength of the ridge, 96L could end up moving even farther south of that prediction. If 96L can manage to sneak past the weakness in the central and western Atlantic, rising heights over the eastern United States and Ohio Valley would allow the system to turn westward at longer ranges.

Any potential talk of any US landfall is still highly premature. Anyone from Texas to New England to Bermuda should monitor the progress of this system. The models may seem tightly clustered, but they have actually been highly unstable. There has literally not been a single model cycle since 96L was tagged where the global models have not shifted significantly in either direction, and an unstable guidance typically suggests fragility in the nuances of the large-scale pattern. Also, if the system interacts with Hispaniola, especially if it's still disorganized, the mountainous terrain on the island could throw a huge wrench into the track. We've seen this with many storms that end up tangling themselves up with the mountains of Hispaniola, the most recent example being Isaac in 2012.

Regardless of development, heavy rainfall and tropical storm force wind gusts will likely overspread portions of the Lesser Antilles during the next day or so before spreading toward the Greater Antilles. A reconnaissance aircraft is scheduled to investigate this disturbance later today, if necessary.

Probability of development in 48 hours: 50%

Probability of development in 120 hours: 70%



Karina

Tropical Storm Karina continues to move across the open Pacific. As of the latest NHC advisory, the following information was posted on Karina:

Wind: 60 mph, with higher gusts
Location: 15.9°N 136.4°W
Movement: Stationary
Pressure: 998 mb

The cloud pattern associated with Karina really hasn't changed much. There's a fair bit of convection, but much of it is south of the center except in a tightly-coiled band currently wrapping around the eastern portion of the tropical cyclone. Upper-tropospheric outflow is fair in all quadrants, indicating an environment of fairly modest vertical shear.



Figure 2. Latest infrared satellite image of Tropical Storm Karina. Image credit: NOAA's Satellite Services Division (SSD).

Karina is currently over SSTs of about 26 to 27C and in an environment of light shear. As long as these conditions persist, some strengthening could occur assuming Lowell doesn't get in the way. The most likely scenario is for Karina to undergo fluctuations in intensity due to these conditions in the short-term, followed by steady weakening later in the period the cyclone is hit by a renewed blast of easterly shear associated with a northwestward-moving Lowell. Karina is forecast to weaken to a tropical depression in four days, and become a remnant low on day five; however, some of the guidance dissipates Karina sooner, and this is not impossible once Lowell takes hold.

Karina is embedded within a region of weak steering between a broad upper-level trough to the northwest, and an equally broad upper-level ridge to the northeast. This is resulting in little net motion of the cyclone, although recent satellite fixes suggest it could have wobbled erratically south of the 0300Z NHC forecast track. Karina is forecast to meander for the next day or so before accelerating northeastward into the circulation associated with Lowell. For such a complex scenario, the models are in surprisingly good agreement on this scenario, as they have been for several days. My forecast is not too dissimilar to the latest model consensus.

Intensity forecast

Initial 08/21 0300Z 15.9°N 136.4°W 50 kt 60 mph
12 hour 08/21 1200Z 15.8°N 136.4°W 50 kt 60 mph
24 hour 08/22 0000Z 15.8°N 136.2°W 50 kt 60 mph
36 hour 08/22 1200Z 15.8°N 135.8°W 50 kt 60 mph
48 hour 08/23 0000Z 16.3°N 134.8°W 45 kt 50 mph
72 hour 08/24 0000Z 18.4°N 130.5°W 40 kt 45 mph
96 hour 08/25 0000Z 21.9°N 128.5°W 30 kt 35 mph
120 hour 08/26 0000Z 27.1°N 129.8°W 25 kt 30 mph; post-tropical/remnant low

Track forecast



Figure 3. My forecast track for Karina.


Lowell

Large Tropical Storm Lowell continues to churn in the Pacific. As of the latest NHC advisory, the following information was posted on the cyclone:

Wind: 65 mph, with higher gusts
Location: 19.6°N 121.6°W
Movement: NW at 3 mph
Pressure: 988 mb

There is some suggestion on infrared satellite imagery that Lowell could be getting better organized this morning. While the outer banding seen radiating to the north of the center has dissipated, rather cold convection has been persisting in the southern semicircle of the tropical cyclone, perhaps a formative eyewall. This convection has been attempting to wrap cyclonically around the northern half of the tropical cyclone, and if it completes, Lowell could briefly become a hurricane. Upper-level outflow remains well-established, suggesting an environment of weak wind shear. Interestingly, the CIMSS Advanced Dvorak Technique (ADT) is lagging the satellite signature, garnering final T numbers of only 2.0, which is only 30 kt. SAB remains more reasonable at 3.5/55 kt.



Figure 5. Latest infrared satellite image of Tropical Storm Lowell. Image credit: NOAA's Satellite Services Division (SSD).

Lowell is currently over 26C SSTs and in an environment of weak wind shear and a moist troposphere. The warm waters should continue for the next 12-18 hours before Lowell crosses the 26C isotherm and begins to weaken. While not explicitly indicated, it is certainly possible that Lowell could briefly reach hurricane status during this time, particularly if current convective trends persist through the forthcoming diurnal convective maximum. Beyond 24 hours, a combination of progressively cooler waters (dropping to 22C by the end of the forecast period) should induce a steady weakening, although it is likely to be slower than normal for decaying cyclones in this region due to the unusually large circulation of Lowell and the likelihood of negligible vertical shear along the forecast track. Remnant low status is shown by day four, as Lowell will be well-embedded in cold waters by that time.

Lowell continues to move toward the northwest on a fairly smooth trajectory. Water vapor imagery shows a mid- to upper-level shortwave over southern California moving southward into the Pacific. This low has recently become quasi-stationary, which lends credibility to the global models which forecast this feature to lift out and allow the subtropical ridge to rebuild to the north of the cyclone, helping promote a more west-northwestward motion in the low-level flow as Lowell becomes a shallow system. The guidance continues to be very stable, and there is high confidence in the forecast track.

Intensity forecast

Initial 08/21 0300Z 19.6°N 121.6°W 55 kt 65 mph
12 hour 08/21 1200Z 20.3°N 122.2°W 60 kt 70 mph
24 hour 08/22 0000Z 21.1°N 122.9°W 60 kt 70 mph
36 hour 08/22 1200Z 21.7°N 123.8°W 55 kt 65 mph
48 hour 08/23 0000Z 22.6°N 124.9°W 50 kt 60 mph
72 hour 08/24 0000Z 24.1°N 126.7°W 40 kt 45 mph
96 hour 08/25 0000Z 26.2°N 129.4°W 30 kt 35 mph: post-tropical/remnant low
120 hour 08/26 0000Z 28.3°N 133.9°W 25 kt 30 mph: post-tropical/remnant low

Track forecast



Figure 5. My forecast track for Lowell.

2014 Atlantic hurricane season 2014 Pacific hurricane season Invest 96L Tropical Storm Karina Tropical Storm Lowell

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Tropical weather analysis - August 19, 2014

By: KoritheMan, 7:06 AM GMT on August 19, 2014

Notice: All forecasts presented here are based upon my own knowledge of atmospheric dynamics. They are created using my knowledge of the various computer models, satellite interpretation, and other tools and parameters. These forecasts, while striving to be accurate, are not intended to supersede predictions by the National Hurricane Center. Always follow NWS protocol and forecasts.



Karina

Tropical Storm Karina has regained some strength over the last 24 hours. As of the 0300Z NHC advisory, the following information was available on the storm:

Wind: 65 mph, with higher gusts
Location: 15.9°N 133.6°W
Movement: WSW at 8 mph
Pressure: 996 mb

Satellite data show significantly warmer cloud tops, although they have recently become cold again in a loose band to the west of the low-level center. The 6z satellite estimates are certainly not impressive, and they suggest that Karina could be a little weaker at this time.



Figure 1. Latest infrared satellite image of Tropical Storm Karina. Image credit: NOAA's Satellite Services Division (SSD).

Karina's renewed struggles appear to be twofold: UW-CIMSS shows about 15 kt averaged 850-200 mb southeasterly shear over the cyclone due to a distant mid- to upper-level ridge. In addition, water vapor imagery and CIMSS TPW data show pockets of dry air to the west and east of the system, which appears to be becoming entrained into the southern portion of the circulation based on arc clouds observed on the south side of the center in satellite photography. This dry air has clearly not been handled well by the models, with most of their weakening due to more to shear than thermodynamics. Since the shear, while still evident, has decreased since yesterday, I will indicate a little bit of intensification while Karina is still over warm water, but I am below the NHC prediction and keep Karina just below hurricane strength. In a few days, the tropical storm will encounter cooler waters and a renewed surge of easterly to northeasterly shear due to outflow from the large circulation of Tropical Storm Lowell, located several hundred miles east of Karina. It is a little difficult to predict exactly how much weakening will occur as Karina interacts with Lowell and begins to decay, with the ECMWF generally suggesting less shear than the GFS at longer ranges. My forecast shows Karina winding down to a 30-kt depression at the end of the forecast period, in reasonable agreement with the GFS model, which shows Karina steadily weakening as it gets rather close to the circulation of Lowell.

Karina appeared to be moving a little north of the NHC forecast track earlier, but perhaps that was an illusion created when the system still had convection. Recent imagery indicates that the cyclone pretty much remains on track, and appears to be moving more westward now. Water vapor imagery shows a broad mid-level ridge stabilizing to the north of Karina, which should induce a westward motion for the next 24 hours, followed by deceleration and a rather sharp turn to the northeast as the circulation becomes more involved with the larger vortex associated with Lowell. All of the model guidance agrees with this scenario, which is surprising considering how aclimatological it is. There are still some differences in forward speed, with the ECMWF slower than the GFS. My forecast trends toward a blend of both.

Intensity forecast

Initial 08/19 0300Z 15.9°N 133.6°W 55 kt 65 mph
12 hour 08/19 1200Z 16.0°N 134.5°W 55 kt 65 mph
24 hour 08/20 0000Z 16.0°N 135.1°W 60 kt 70 mph
36 hour 08/20 1200Z 16.4°N 135.4°W 60 kt 70 mph
48 hour 08/21 0000Z 17.1°N 134.9°W 55 kt 65 mph
72 hour 08/22 0000Z 17.8°N 134.4°W 45 kt 50 mph
96 hour 08/23 0000Z 18.6°N 133.8°W 35 kt 40 mph
120 hour 08/24 0000Z 19.3°N 133.4°W 30 kt 35 mph

Track forecast



Figure 2. My forecast track for Karina.



Lowell

Large Tropical Storm Lowell continues to spin the eastern Pacific. As of the latest NHC advisory, the following information was posted on the storm:

Wind: 40 mph, with higher gusts
Location: 17.0°N 118.6°W
Movement: WNW at 7 mph
Pressure: 1000 mb

Satellite data shows that Lowell remains a very large tropical cyclone with a large radius of maximum winds and little in the way an organized inner core.



Figure 3. Latest infrared satellite image of Tropical Storm Lowell. Image credit: NOAA's Satellite Services Division (SSD).

Lowell is producing some rather deep convection -- colder than -80C -- in a large band south of the center. It is a little difficult identifying the center of circulation since the circulation is so large and elongated, but I assume it is well to the north of the -80C convection, although it doesn't appear to be fully exposed, either. Assuming that Lowell's circulation is a little closer to the deep convection, or even if it's not... if that convection can persist and wrap cyclonically into the center, some intensification could occur while Lowell remains over warm water and in an environment of moderate east-northeasterly wind shear. The shear appears to be more concentrated at the middle-troposphere rather than the upper-troposphere as evident by the cyclone's rather impressive outflow pattern on satellite imagery. It appears unlikely that Lowell will become a hurricane due to the large and sprawling nature of the cyclone vortex, although one can never quite rule that out with complete certainty. My forecast shows Lowell peaking at 55 kt in 48 hours, higher than the majority of guidance, and 5 kt higher than the 0300Z NHC intensity prediction scheme. Beyond that time, Lowell will encounter waters that cool only gradually first, but then do so quite rapidly later on. This should lead to weakening even though the shear is forecast to remain generally light for the next several days. Nevertheless, large circulations like Lowell frequently take a long time to spin down, and I suspect that we will still be tracking a remnant low over a week from now.

As I mentioned above, locating the broad center of Lowell is not easy, even with passive microwave imagery to assist me. It still appears to be moving northwestward roughly in line with the latest NHC forecast track, at least if we track the entire cloud system center and not jump on any random convective bursts within the gyre. Water vapor imagery shows a broad and distant mid-level ridge to the northeast of Lowell, while a cold low and trailing mid- to upper-level trough dig southward along California and into the eastern Pacific. The global models suggest that the unseasonably deep trough associated with the upper low will erode the western periphery of the subtropical ridge, allowing Lowell to continue moving northwestward to north-northwestward for the next 48 hours, which is consistent with current trends. Subsequently, the guidance shows Lowell's track bending a little to the left as mid-level ridging redevelops to the north of the storm as the trough lifts out. The TVCA model consensus has shifted left at 0z once again, and my forecast track closely mimics that guidance. I would not be surprised to see additional westward shifts by the model consensus, the NHC, and myself over the next couple of days.

Intensity forecast

Initial 08/19 0300Z 17.0°N 118.6°W 35 kt 40 mph
12 hour 08/19 1200Z 17.6°N 119.3°W 40 kt 45 mph
24 hour 08/20 0000Z 18.3°N 120.0°W 45 kt 50 mph
36 hour 08/21 1200Z 19.2°N 120.6°W 50 kt 60 mph
48 hour 08/22 0000Z 20.1°N 121.1°W 55 kt 65 mph
72 hour 08/23 0000Z 22.0°N 123.1°W 50 kt 60 mph
96 hour 08/24 0000Z 23.7°N 125.1°W 40 kt 45 mph
120 hour 08/25 0000Z 25.1°N 127.7°W 30 kt 35 mph: post-tropical/remnant low

Track forecast



Figure 4. My forecast track for Lowell.

2014 Pacific hurricane season Tropical Storm Karina Tropical Storm Lowell

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Tropical weather analysis - August 18, 2014

By: KoritheMan, 7:24 AM GMT on August 18, 2014

Notice: All forecasts presented here are based upon my own knowledge of atmospheric dynamics. They are created using my knowledge of the various computer models, satellite interpretation, and other tools and parameters. These forecasts, while striving to be accurate, are not intended to supersede predictions by the National Hurricane Center. Always follow NWS protocol and forecasts.

Karina

Karina continues as a minimal tropical storm over the open eastern Pacific. As of the 0300Z NHC advisory, the following information was posted on the system:

Wind: 45 mph, with higher gusts
Location: 17.5°N 130.4°W
Movement: WSW at 12 mph
Pressure: 1002 mb

Karina remains a sheared tropical cyclone, with the low-level center remaining well-defined but exposed to the east of the convection due to about 15 kt of east-northeasterly shear as denoted by UW-CIMSS; this shear appears to be caused by newly-formed Tropical Depression Twelve-E to the east, and also a distant mid- to upper-level ridge located near the southwestern coast of Mexico. Satellite estimates from SAB and CIMSS actually don't quite support a 40 kt intensity as of this writing, which suggests that Karina could be a little weaker, coincident with a recent warming of the convective cloud tops.



Figure 1. Latest infrared satellite image of Tropical Storm Karina. Image credit: NOAA's Satellite Services Division (SSD).

Karina's future remains riddled with uncertainty. The present easterly shear is forecast by the GFS and ECMWF global models to diminish during the next 24 hours, which, if true, should allow for Karina to strengthen, or at least stop weakening. The shear should theoretically lessen as the cyclone moves farther away from the axis of the aforementioned ridge, and also while Karina gains some distance from Tropical Depression Twelve-E, so I've elected to show some modest restrengthening during this time. While some of the guidance suggests continued strengthening after that, with the GFDL and HWRF even suggestive of Karina regaining hurricane status, these forecasts are likely based on the GFS forecast fields which show what I suspect is less shear than will occur in actuality. Toward the end of the forecast period, shear is likely to increase again as 12-E becomes an even deeper system with a broadened anticyclone; combined with SSTs of only around 26C, and the result should be weakening.

Karina's motion has been easy to follow this evening due to the exposed nature of the low-level center. It appears to still be moving west-southwest and moving along the general trajectory of the National Hurricane Center track. The motion of Karina is being controlled by a mid-tropospheric high pressure system to the north of the tropical storm. The model guidance forecasts a small break in the ridge in about 48 hours, which should allow Karina to gain some latitude at that time. While the guidance is in good agreement about this scenario, there are significant differences in how far east Karina is liable to move as the circulation of 12-E consolidates and begins to dominate this portion of the eastern Pacific with a large fetch of low- to mid-level westerly winds. The TVCA model consensus has not been particularly stable when the anticipated eastward regression of Karina begins, and it is probably best not to jump on any subtle model shifts that typically accompany each cycle until the extent of this turn becomes more clear. My forecast track is similar to the current National Hurricane Center prediction, but is a little farther north, especially initially.

Intensity forecast

Initial 08/18 0300Z 17.5°N 130.4°W 40 kt 45 mph
12 hour 08/18 1200Z 17.3°N 131.4°W 40 kt 45 mph
24 hour 08/19 0000Z 16.9°N 132.5°W 40 kt 45 mph
36 hour 08/19 1200Z 16.8°N 133.4°W 45 kt 50 mph
48 hour 08/20 0000Z 16.9°N 134.5°W 45 kt 50 mph
72 hour 08/21 0000Z 17.1°N 135.7°W 45 kt 50 mph
96 hour 08/22 0000Z 17.2°N 136.0°W 40 kt 45 mph
120 hour 08/23 0000Z 18.1°N 134.7°W 40 kt 45 mph

Track forecast



Figure 2. My forecast track for Karina.



Tropical Depression Twelve-E

Tropical Depression Twelve-E is located several hundred miles east of Karina. As of the 0300Z NHC advisory, the following information was posted on the depression:

Wind: 35 mph, with higher gusts
Location: 16.1°N 116.6°W
Movement: W at 8 mph
Pressure: 1005 mb

The cyclone is producing considerable deep convection in large bands west of the center, but the convection over the center is neither abundant nor especially well-organized. Dvorak numbers haven't changed appreciably, and the cyclone is not going to immediately become a tropical storm. It should be noted that the depression is currently in an environment of very light vertical wind shear, as denoted by the pronounced and well-defined upper-tropospheric outflow pattern.



Figure 3. Latest infrared satellite image of Tropical Depression Twelve-E. Image credit: NOAA's Satellite Services Division (SSD).

The depression will remain over warm waters through about the next 48 hours. Given that, the light shear and the seemingly little dry air, the depression is likely to become a tropical storm in the next 12 hours. While these conditions would ordinarily portend rapid intensification, satellite images suggest that the depression has an atypically large circulation, which will act to limit the amount of strengthening that can occur. My forecast shows a peak of 50 kt in about 48 hours, which is in line with most of the guidance. Subsequent to 48 hours, waters cool -- slowly at first, then increasingly more rapidly later on -- which should begin to weaken the cyclone even though the shear is forecast to remain generally low. The ECMWF shows somewhat stronger southerly shear afflicting the system at day five, but it remains to be seen how much shear will actually be present to afflict the storm; there certainly isn't much of it on water vapor imagery at the moment. Waters become quite cold by day five, so the cyclone is likely to become a convectiveless remnant area of low pressure by that time. Extratropical transition does not currently appear to be a viable scenario at longer ranges, as the models show the cyclone remaining in the warm sector of a broad upper-level trough over the western United States. It is not out of the question that the depression could briefly become a hurricane before sea surface temperatures beneath the storm cool, but it will take a lot to consolidate such a sprawling and still broad circulation.

The motion of the cyclone is not an easy thing to determine this evening, largely due to the still elongated nature of the vortex. Based on a slew of comparative microwave passes and shortwave infrared satellite-derived low cloud motions, it appears that the depression may have actually begun moving a little south-of-west, perhaps in response to an unexpectedly strong subtropical ridge in the local vicinity of the depression; my forecast is thus a little south of the current model consensus in the short-term. Water vapor imagery shows an upper-level low over interior western California moving southward. The global models show this feature deepening and enhancing the synoptic cyclonicity currently encompassing much of the eastern Pacific from north of Hawaii to the California coast. This predicted evolution should drive the cyclone northwestward for the next first 48 hours, followed by a more north-northwesterly to northerly motion afterward. My forecast track is in best agreement with the ECMWF, although it remains a little to the right of that model. This forecast is also to the right of 0300Z National Hurricane Center prediction.

It is interesting to note that most of the global models show the center of the decaying cyclone getting very close to the southern California coast in about a week; some of these modeled representations depict an actual tropical cyclone, albeit weak. I strongly suspect that, as unique as this scenario is, it is one that will decidedly not verify due to the climatological pool of cold water intrinsic to the California coast. Nevertheless, sea surface temperatures are anywhere between 2 and 4C above average off the west coast of the United States and along the projected path of the depression, so it may be able to remain stronger than usual over the cold water. I actually hate bringing California into this, especially this early, but I felt it was worth pointing out a rare near consensus in the models to aim the depression up that way.

After dissipation, the remnant mid-level moisture of the tropical cyclone could stream northward along the trough and enhance rainfall over portions of southern California and the southwestern United States.

Intensity forecast

Initial 08/18 0300Z 16.1°N 116.6°W 30 kt 35 mph
12 hour 08/18 1200Z 16.4°N 117.8°W 35 kt 40 mph
24 hour 08/19 0000Z 16.9°N 118.7°W 40 kt 45 mph
36 hour 08/19 1200Z 18.0°N 119.4°W 45 kt 50 mph
48 hour 08/20 0000Z 19.1°N 119.9°W 50 kt 60 mph
72 hour 08/21 0000Z 20.5°N 120.3°W 50 kt 60 mph
96 hour 08/22 0000Z 22.9°N 121.1°W 40 kt 45 mph
120 hour 08/23 0000Z 25.1°N 121.7°W 30 kt 35 mph: post-tropical/remnant low

Track forecast



Figure 4. My forecast track for Tropical Depression Twelve-E.

2014 Atlantic hurricane season 2014 Pacific hurricane season Tropical Storm Karina Tropical Depression Twelve-E

Updated: 7:35 AM GMT on August 18, 2014

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Tropical weather analysis - August 16, 2014

By: KoritheMan, 6:23 AM GMT on August 16, 2014

Notice: All forecasts presented here are based upon my own knowledge of atmospheric dynamics. They are created using my knowledge of the various computer models, satellite interpretation, and other tools and parameters. These forecasts, while striving to be accurate, are not intended to supersede predictions by the National Hurricane Center. Always follow NWS protocol and forecasts.

Karina

Tropical Storm Karina continues to struggle with high wind shear over the open eastern Pacific. As of the 0300Z NHC advisory bulletin, the following information was available on the storm:

Wind: 45 mph, with higher gusts
Location: 17.8°N 122.0°W
Movement: W at 10 mph
Pressure: 1002 mb

Karina continues to resemble a sheared tropical cyclone on satellite pictures this evening. The low-level center remains partially exposed along the northeastern side of the convection due to about 25 kt of easterly shear according to the 0300Z CIMSS 850-200 mb averaged wind shear data; the SHIPS analyzes a good bit less, but in either case there is shear over Karina. This shear is being imparted by a large amplitude upper-level anticyclone centered between Karina and the southwestern Baja Peninsula, invigorated a bit perhaps by the area of disturbed weather to the southeast of Karina. A blend of the satellite estimates suggests that the National Hurricane Center's current 40-kt intensity assignment is a good one.



Figure 1. Latest infrared satellite image of Tropical Storm Karina. Image credit: NOAA's Satellite Services Division (SSD).

The GFS, ECMWF, and the SHIPS, which is based off the GFS parameters, do not foresee an appreciable decrease in shear until around 60-72 hours, when they suggest the environment could become a lot more favorable as far as the upper-level winds are concerned; this is also supported by water vapor analyses. During that period, some of the models show Karina reintensifying as it takes seizes the opportunity of low shear. Since the SHIPS model SST integration still appears once again a little too cold, a restrengthening scenario is not out of the question at those times. Having said that, I am not quite ready to commit my forecast to that scenario yet, in deference to the potential for interaction of Karina with either the aforementioned area of disturbed weather to its east, or another one in the central Pacific located to the west of the tropical storm, an interaction which could certainly create shear for our struggling tropical cyclone. I would not be surprised, however, to see Karina strengthen during the latter half of the forecast, particularly if the large area of stable air to the north of the cyclone does not become entrained into the circulation during the next few days. For now though, I feel it's best to keep Karina steady state throughout the forecast period, with personal acknowledgement that I could definitely be wrong in either direction.

Karina appears to have sped up a little relative to the 0300Z NHC forecast package, and my own forecast track has reflected that accordingly. Synoptic data indicates that Karina is south of a well-established subtropical ridge. The global model 500 mb height fields forecast this feature to persist and build westward ahead of the cyclone, a situation that appears to be gradually occurring as a large-scale upper-level trough moves into the western United States and bypasses Karina. A westward motion should begin soon, with a gradual turn to the west-southwest anticipated as the cyclone nears 130W. At days four and five, a significant slowing of the forward speed is expected as a broad upper-level trough begins to amplify to the west of Hawaii, concurrent with the resumption of a westward motion. The slow westward motion at those times is also my way of attempting to be cautious and blend the possibilities of binary interaction with disturbances/cyclones to the east and west of Karina. Currently the one in the central Pacific appears to be developing a little faster, albeit in a pulsating fashion, so I would expect more interaction with that disturbance.

Intensity forecast

Initial 08/16 0600Z 18.1°N 122.9°W 40 kt 45 mph
12 hour 08/16 1800Z 18.2°N 124.5°W 40 kt 45 mph
24 hour 08/17 0600Z 18.2°N 126.3°W 40 kt 45 mph
36 hour 08/17 1800Z 18.1°N 128.2°W 40 kt 45 mph
48 hour 08/18 0600Z 17.8°N 130.0°W 40 kt 45 mph
72 hour 08/19 0600Z 17.5°N 132.3°W 40 kt 45 mph
96 hour 08/20 0600Z 17.5°N 133.0°W 40 kt 45 mph
120 hour 08/21 0600Z 17.5°N 133.6°W 40 kt 45 mph

Track forecast



Figure 2. My forecast track for Karina.



Invest 95L

An area of disturbed weather over the far eastern Atlantic roughly midway between the west coast of Africa and the Cape Verde Islands (95L) is showing signs of organization. Evening satellite data suggest that low-level center is probably located within the eastern edge of the convection due to about 15 kt of southeasterly shear from a broad and distant mid- to upper-level ridge centered over northwestern Africa. The shear aside, convection continues to persist near and just west of the apparent low-level center, which an earlier ASCAT pass (shown below) just before 0000 UTC suggested was quite well-defined, even producing some believable 25-kt surface winds not far south of the tropical wave axis. Considering the notorious low bias of the ASCAT, these winds are likely closer to 30 kt.



Figure 3. Latest infrared satellite image of Invest 95L. Image credit: Regional and Mesoscale Meteorology Branch (RAMMB), Colorado State University (CSU).

It would not take much of an increase in organization for the system to be declared a tropical cyclone overnight. Interests in the Cape Verde Islands should carefully assess and monitor the progress of this system, as squally weather, including tropical storm force winds and heavy rain, is likely to afflict much of the islands during the next 24 hours. I imagine the NHC would issue a short-fuse tropical storm warning for much of, if not at all of the archipelago in the event a tropical depression or tropical storm formed overnight.



Figure 4. ASCAT pass taken at 2259 UTC. Notice the well-defined and already closed surface wind circulation in connection with this tropical wave. The resolution is 25 km, allowing us to see more of the wind structure.

Even if the system becomes a tropical cyclone, its future is highly uncertain. Water vapor imagery shows a broad mid- to upper-level trough over the central Atlantic near the Azores southward. This synoptic feature could in theory induce shear over the disturbance as it moves across the Atlantic, but the GFS and ECMWF suggest the shear could be more southerly than southwesterly, a condition which is much more favorable for wave amplification. In addition, there is currently not much evidence that this trough is digging much, with northerly flow enveloping the area from near 30N 35W westward to 50W, suggesting more ridging than troughing. My guess is that there will not be a lot of shear over the wave over the next few days, but there is of course the seemingly unassailable wall of dry air still plaguing the MDR; also, 95L will be moving across cooler sea surface temperatures during the next couple of days before waters begin warming again between 72 and 120 hours.

I expect more of a west-northwestward motion initially, followed by a turn to the west as the subtropical ridge establishes itself to the north of 95L. The GFS and ECMWF suggest that a weakness could exist south of Newfoundland extending to near Bermuda as the system traverses the central Atlantic, but this weakness may not be enough to recurve a shallow system, and a ridge is likely to park itself over the eastern United States if the system can slide under the weakness. A continued westward to west-northwestward motion appears likely through at least the next 5 - 7 days. It is too early to speculate on any potential land impact other than the Cape Verde Islands, and in all honesty, I suspect it is more likely than not that this disturbance just ends up being another tease and ultimately croaks to death in the MDR... a situation that I fancy even if it becomes a tropical cyclone. If it does die off early, it will need to be carefully monitored as it gets farther westward into potentially more favorable conditions near and west of 60W.

Probability of development in 48 hours: 50%

Probability of development in 120 hours: 50%

2014 Atlantic hurricane season 2014 Pacific hurricane season Tropical Storm Karina Invest 95L

Updated: 6:53 AM GMT on August 16, 2014

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Tropical weather analysis - August 13, 2014

By: KoritheMan, 6:38 AM GMT on August 13, 2014

Notice: All forecasts presented here are based upon my own knowledge of atmospheric dynamics. They are created using my knowledge of the various computer models, satellite interpretation, and other tools and parameters. These forecasts, while striving to be accurate, are not intended to supersede predictions by the National Hurricane Center. Always follow NWS protocol and forecasts.

Tropical Depression Eleven-E

The area of disturbed weather that has paralleled the Mexican coast over the last few days has become a tropical depression. As of the 0300Z NHC advisory, the following information was posted on the system:

Wind: 35 mph, with higher gusts
Location: 16.5°N 108.5°W
Movement: WNW at 16 mph
Pressure: 1006 mb

The depression appears to be getting better organized, and it will likely become Tropical Storm Karina in short order. Satellite data indicates the formation of curved bands to the west of the center, and a small burst of cold convection over the center proper. The outflow pattern is well-defined, with a northerly upper jet moving off the mountains of southwestern Mexico just to the east of the cyclone and enhancing the outflow in that region. In addition, the outflow appears to be excellent to the west, with the turning of the cirrus in that quadrant signifying the possibility of a large upper ridge building over the cyclone center. Earlier microwave data suggested that the center was just outside the convection on the southeast side of the thunderstorms, but recent satellite pictures indicate that it is likely under the convection now.



Figure 1. Latest infrared satellite image of Tropical Depression Eleven-E. Image credit: NOAA's Satellite Services Division (SSD).

Environmental conditions appear favorable continued intensification, possibly even rapid if an inner core can become established. The SHIPS rapid intensification parameter shows a 34% chance of a 25-kt increase in winds during the next 24 hours, and I would not be surprised to see this suggestion increase with subsequent runs. My forecast is below the SHIPS but above most of the remaining intensity guidance, showing a peak of 80 kt in 96 hours. The only reason I did not go higher was because water vapor imagery shows cirrus ahead of the system along the system's trajectory from about 113W westward to about 123W, the direction of the cirrus indicating easterly to southeasterly shear. While it could be possible that this shear will get more anticyclonic with time, I am not yet convinced enough to justify a higher forecast intensity. If the shear appears less apparent tomorrow, and if current organization trends continue within the inner structure of the depression, my next forecast could show a significantly stronger cyclone. It is not out of the question at all that we could see the sixth major hurricane of the season originate from this depression, since it still has about four days over 27-28C SSTs according to areal sea surface temperature analyses; indeed, the SHIPS SST assimilation currently appears about a degree (C) too cold, a situation which has been thematic for the previous few Pacific storms. A weakening is shown after day four as the cyclone enters somewhat cooler SSTs, but with little vertical shear forecast by the GFS or ECMWF, I sense another annular hurricane may be looming. Interesting few days ahead.

The depression appears to have sped up, and may also be passing a little to the north of the 12z NHC forecast point. Water vapor imagery shows a broad mid- to upper-level trough just off the coast of California moving southeastward. The global model 500 mb height fields suggest that the cold low trailing this trough will move eastward into California over the next day or so, allowing the small weakness in the ridge to fill and propel the system on a westward track. Under the assumption that the cold low will not disappear as quickly as the models are suggesting leads me to forecast a 12-hour motion that is more toward the west-northwest. However, since the depression appears to have sped up, it is possible my forecast track could be too far north initially as the cyclone outruns the low and feels the stronger mid-level ridging found to the west of that low. After the initial west-northwest motion, a turn to the west is anticipated as the cyclone comes under a rather strong mid-level ridge. While there is general agreement on this scenario, some disparity arises in between the guidance a little later in the period, with many of the members suggesting either a turn to the southwest or a slow and erratic motion near the end of the period as the cyclone interacts with another modeled disturbance in the ITCZ to its southeast. Since this interaction appears to be getting overdone given the depth of the cyclone in both the model fields and presently, my forecast track indicates no such motion, but instead continues the generally westward motion to the south of the ridge. This forecast is north of the TVCA model consensus, and is fairly similar to the current NHC prediction, except a little faster given current motion trends.

Intensity forecast

Initial 08/13 0300Z 16.5°N 108.5°W 30 kt 35 mph
12 hour 08/13 1200Z 16.7°N 110.8°W 35 kt 40 mph
24 hour 08/14 0000Z 16.7°N 113.4°W 40 kt 45 mph
36 hour 08/14 1200Z 16.7°N 116.0°W 45 kt 50 mph
48 hour 08/15 0000Z 16.7°N 119..0°W 55 kt 65 mph
72 hour 08/16 0000Z 16.8°N 122.7°W 70 kt 80 mph
96 hour 08/17 0000Z 16.9°N 125.4°W 80 kt 90 mph
120 hour 08/18 0000Z 17.2°N 128.6°W 70 kt 80 mph

Track forecast



Figure 2. My forecast track for Tropical Depression Eleven-E.



Julio

Julio has regained hurricane status as of the 0300Z CPHC advisory bulletin:

Wind: 75 mph, with higher gusts
Location: 29.4°N 158.0°W
Movement: NW at 7 mph
Pressure: 989 mb

The cloud pattern of Julio has changed little since the previous advisory. Convection has taken on less outer banding and a more prominent limitation to the broad eyewall structure. The latest SAB estimate supports the CPHC's 65 kt intensity. Interestingly, the UW-CIMSS technique appears to be running quite far behind the satellite signature, with the latest final T numbers coming in at only 2.8. Upper-tropospheric outflow is expanding to the west, heralding a decrease in southwesterly shear.



Figure 3. Latest infrared satellite image of Hurricane Julio. Image credit: NOAA's Satellite Services Division (SSD).

Despite Julio's hopefully last accolade, its nomination to hurricane status is likely to be short-lived. The models forecast a rather sharp increase in northeasterly to northerly vertical shear beginning in about 24 hours and persisting throughout the forecast period, as the broad cyclonic zone of troughiness between Alaska and Julio moves eastward in tandem with the high-latitude hurricane. The shear could easily exceed 40 kt if the GFS and ECMWF are correct, which will be extremely prohibitive to a northeastward-moving system. Actually, it is entirely possible Julio could weaken faster than I've suggested below, but most of the guidance still hangs onto the system for at least the next four days, but they could of course be underestimating the deleterious effect of the shear. I would also like to see if the high shear values seen on the GFS/ECMWF fields verifies before I decide to terminate Julio too quickly. It is possible my next forecast will have to show a quicker demise.

Julio appears to be moving northwest, and is following the current CPHC prediction rather behaviorally. There is far less spread in the guidance than there has been, although there is still some differences on the sharpness and onset of recurvature. The ECMWF is to the left of the GFS and shows Julio moving northward as it slowly decays, whlie the GFDL and HWRF show a similar trajectory to the GFS, but ended up slower and farther south, instead showing a sheared system stalling south of 35N. This is likely in response to the anticipated shear, and I have actually blended this solution into my forecast at the end of the period, as I feel it is a viable one; strong shear can often retard speedy movement in the direction of the shear, and that is what I have shown below, with Julio likely to move slowly northward between 72 and 96 hours as it begins to feel the shear, and is also steered by a low- to mid-level ridge to the east. This forecast is not too dissimilar to the current CPHC prediction, and favors the GFS solution over the ECMWF, as that model has been handling this hurricane well for days.

Intensity forecast

Initial 08/13 0300Z 29.4°N 158.0°W 65 kt 75 mph
12 hour 08/13 1200Z 30.0°N 158.6°W 65 kt 75 mph
24 hour 08/14 0000Z 30.5°N 158.7°W 60 kt 70 mph
36 hour 08/14 1200Z 31.3°N 158.4°W 50 kt 60 mph
48 hour 08/15 0000Z 32.4°N 157.5°W 45 kt 50 mph
72 hour 08/16 0000Z 33.4°N 156.6°W 35 kt 40 mph
96 hour 08/17 0000Z 34.0°N 156.6°W 30 kt: post-tropical/remmant low
120 hour 08/18 0000Z: dissipated

Track forecast



Figure 4. My forecast track for Julio.

2014 Pacific hurricane season Tropical Depression Eleven-E Hurricane Julio

Updated: 6:48 AM GMT on August 13, 2014

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Tropical weather analysis - August 11, 2014

By: KoritheMan, 6:56 AM GMT on August 11, 2014

Notice: All forecasts presented here are based upon my own knowledge of atmospheric dynamics. They are created using my knowledge of the various computer models, satellite interpretation, and other tools and parameters. These forecasts, while striving to be accurate, are not intended to supersede predictions by the National Hurricane Center. Always follow NWS protocol and forecasts.

Julio

Hurricane Julio continues heading across the open Pacific well away from land. As of the 0300Z CPHC advisory bulletin, the following information was posted on the hurricane:

Wind: 85 mph, with higher gusts
Location: 25.5°N 153.5°W
Movement: NW at 13 mph
Pressure: 984 mb
Category: 1 (Saffir-Simpson Hurricane Wind Scale)

Julio's cloud pattern continues to gradually deteriorate. There is still considerable deep convection occurring near the center, but it is neither organized nor persistent; indeed, pulsating storms are indications that the environment is not favorable. Satellite estimates are falling, and it is possible Julio could be weaker than the 3Z operational intensity estimate by this point. Recent microwave data still shows some indications of a remnant mid-level eye, but even this feature is steadily disintegrating.



Figure 1. Latest infrared satellite image of Hurricane Julio. Image credit: NOAA's Satellite Services Division (SSD).

Julio is forecast to steadily weaken throughout the forecast period. The cyclone is currently being impacted by southwesterly shear associated with a broad mid- to upper-level trough located a few hundred miles north of the hurricane, which has caused the outflow in the western quadrant to take on a southwest-to-northeast orientation in tandem with the upper-level shear vector. The GFS and ECMWF connote various levels of shear over the next several days, but in general they appear to want to relax the upper flow over Julio between the 36-72 hour period (which I don't show due to the limitations of the map I use to draw track forecasts, and consequently forecast points), presumably in response to overhead ridging in the wake of the aforementioned trough. After that time, shear is forecast to increase again ahead of another, much larger upper-level trough now over the Bering Sea. Also, sea surface temperatures should remain around 25C throughout the next five days as Julio climbs toward higher latitudes, making reintensification unlikely even if the shear decreases. Actually, the hurricane could very well weaken faster than I what have shown here during the first 12-24 hours of the forecast.

Julio appears to be following the forecast track, as the 500 mb synoptic pattern remains decidedly straightforward. As mentioned previously, water vapor imagery projects an eastward-moving shortwave trough to the north of the hurricane. The global models show a low- to mid-level ridge temporarily replacing the trough in about 24 hours, so a more northwestward motion is expected at that time. While I've not indicated a forecast point beyond 48 hours here, there is some major disagreement amongst the models as to whether Julio will continue generally westward under a presumably deeper ridge, or if it will continue to move northwest before the ridge breaks again with the arrival of the second trough, which would coincide with an abrupt northward and northeastward acceleration into the mid-latitude westerlies. The ECMWF, CMC, and UKMET are to the left, while the GFS, GFDL, and HWRF are to the right. Based on current trends, I prefer the latter camp. This is also close to the latest CPHC prediction.

Intensity forecast

Initial 08/12 0300Z 25.5°N 153.5°W 75 kt 85 mph
12 hour 08/12 1200Z 26.4°N 154.1°W 70 kt 80 mph
24 hour 08/13 0000Z 27.2°N 155.1°W 65 kt 75 mph
36 hour 08/13 1200Z 28.1°N 156.4°W 60 kt 70 mph
48 hour 08/14 0000Z 28.9°N 157.6°W 55 kt 65 mph

Track forecast



Figure 2. My forecast track for Julio.



Invest 99E

A weak area of disturbed weather located a couple hundred miles south of the coast of southern Mexico remains disorganized, with no deep convection near the center. Water vapor imagery shows strong upper-level winds over the system in response to a downstream ridge, but the GFS and ECMWF show this flow relaxing over the next few days, which should allow for some gradual development. In fact, it actually appears as though the shear may not increase as much previously thought, and shortwave infrared satellite pictures compliment the latest UW-CIMSS vorticity analyses by showing increasing low- to mid-tropospheric vorticity associated with the cloud center.



Figure 3. Latest infrared satellite image of Invest 99E. Image credit: NOAA's Satellite Services Division (SSD).

This disturbance is likely to move westward or west-northwestward over the next several days, and will likely not threaten land. It is likely to become a tropical depression sometime this week.

Probability of development in 48 hours: 20%

Probability of development in 120 hours: 70%



Invest 94L

A tropical wave over the eastern Atlantic ("94L") is located just south of the Cape Verde Islands. Satellite images show that the system has recently lost all of its deep convection, likely due to 25-30 kt of easterly shear associated with a deep-layer ridge, and perhaps a bit of dry air. Water vapor imagery still shows that much of the MDR remains littered with dry air, with the latest UW-CIMSS Total Precipitable Water (TPW) animations showing the subsident portion of the Bermuda/Azores ridge slinging this dry air in the general direction of 94L rather nicely.



Figure 4. Latest infrared satellite image of Invest 94L. Image credit: NOAA's Satellite Services Division (SSD).

Upper-level winds may improve a little as the system heads westward and eventually west-northwestward, but are likely to remain generally unfavorable as the system heads either into or just north of the Caribbean. Although a little early to speculate on what is most likely going to be another innocuous tropical wave in a shear-ridden Atlantic, it should be noted that both the GFS and ECMWF show the developing mid- to upper-level trough over the eastern United States departing a little faster than they have been, with the trough likely to be replaced by ridging in about six or seven days. So assuming 94L hasn't gained enough latitude to where recurvature is inevitable, it is not out of the question that it could begin heading more westward by this time next week.

Probability of development in 48 hours: 0%

Probability of development in 120 hours: 30%

2014 Atlantic hurricane season 2014 Pacific hurricane season Hurricane Julio Invest 94E Invest 94L Invest 99E

Updated: 6:56 AM GMT on August 11, 2014

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Tropical weather analysis - August 9, 2014

By: KoritheMan, 6:04 AM GMT on August 09, 2014

Notice: All forecasts presented here are based upon my own knowledge of atmospheric dynamics. They are created using my knowledge of the various computer models, satellite interpretation, and other tools and parameters. These forecasts, while striving to be accurate, are not intended to supersede predictions by the National Hurricane Center. Always follow NWS protocol and forecasts.

Julio

Julio continues moving across the central Pacific as a hurricane. As of the 0300Z CPHC advisory bulletin, the following coordinates were given on the hurricane:

Wind: 100 mph, with higher gusts
Location: 18.9°N 144.7°W
Movement: WNW at 16 mph
Pressure: 970 mb
Category: 2 (Saffir-Simpson Hurricane Wind Scale)

Satellite imagery shows that Julio continues to slowly weaken over cool water, with the latest SHIPS file showing an approximate SST value of 25.4C. That file, along with other regional sea surface temperature analyses, indicates that those waters are the coldest Julio will encounter along the forecast track, but for now they're certainly doing their job expediently. A recently-received 343Z SSMIS microwave pass, however, still shows a formidable eastern eyewall, with the eye apparently open to the west. Upper-tropospheric outflow continues to be relatively well-defined, implying a continued environment of weak vertical wind shear.



Figure 1. Latest infrared satellite image of Hurricane Julio. Image credit: NOAA's Satellite Services Division (SSD).

The intensity forecast for Julio may prove a bit difficult. On one hand, as previously mentioned, the hurricane is now moving across the coldest waters it will encounter along the forecast track. While the waters only gradually warm, any additional input of heat will provide a tropical cyclone with enormous amounts of energy. However, water vapor imagery shows upper-level cirrus debris blowing southwest to northeast not far to the west of Julio, suggesting that wind shear may increase over the hurricane sooner rather than later. Indeed, looking at the models runs this evening, it is apparent that both the GFS and ECMWF foresee an increase in southwesterly shear beginning in around 36 hours. Given current trends on water vapor imagery, I hold that forecast with the utmost predilection. By day four, the models show shear relaxing, and even though the limitations of the map I create my forecast tracks on doesn't allow me to indicate a forecast point beyond 72 hours, an abrupt halt to the expected weakening appears likely at that time, especially since waters warm to around 27C to the north of the Hawaiian Islands. Also, while I'm not explicitly anticipating it at this time, it is possible that some restrengthening could occur at longer ranges as the shear abates and the waters warm, a scenario which is now supported by some of the intensity guidance.

While Julio has been moving generally toward the west-northwest, recent satellite data suggests more of a jog to the north-northwest. This is assumed to be a temporary motion, with model data and real-time synoptic observations still supporting a continued west-northwestward motion over the next several days. While there exists some notable disagreements on the approximate latitude at which Julio will turn, all of the global and dynamical models show the cyclone bending to the left after about 72 hours, with the ECMWF showing a sharper westward turn than the GFS. Overall, the guidance remains in good agreement on Julio passing well north of the Hawaiian Islands, and the southern fringes of the cone of uncertainty no longer lies over the state. Until that turn becomes more definite, however, interests there should continue to carefully assess future forecasts on Julio. On the current track, Julio's rains and winds will miss the islands, but it will cause a disruption of the normally uniform trade wind flow, and could also generate some high surf.

Intensity forecast

Initial 08/09 0300Z 18.9°N 144.7°W 85 kt 100 mph
12 hour 08/09 1200Z 19.9°N 146.9°W 80 kt 90 mph
24 hour 08/10 0000Z 21.1°N 149.7°W 75 kt 85 mph
36 hour 08/10 1200Z 22.4°N 151.8°W 65 kt 75 mph
48 hour 08/11 0000Z 23.7°N 154.7°W 60 kt 70 mph
72 hour 08/12 0000Z 25.4°N 157.7°W 50 kt 60 mph

Track forecast



Figure 2. My forecast track for Julio.

2014 Pacific hurricane season Hurricane Julio

Updated: 6:05 AM GMT on August 09, 2014

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Tropical weather analysis - August 8, 2014

By: KoritheMan, 8:08 AM GMT on August 08, 2014

Iselle

Iselle continues to head toward the Big Island. As of the 6z CPHC intermediate advisory, the following information was posted:

Wind: 75 mph, with higher gusts
Location: 18.9°N 154.4°W
Movement: W at 15 mph
Pressure: 992 mb
Category: 1 (Saffir-Simpson Hurricane Wind Scale)

After a brief period of reintensification 24 hours ago, Iselle has done a complete turnaround. Satellite images show a substantial decrease in central convection, with the coldest cloud tops only around -50C near the apparent center. In addition, flight-level and surface wind data from a hurricane hunter aircraft investigating the cyclone has so far not found winds strong enough to support hurricane strength. While the CPHC perhaps wisely opted to hold the 6z initial intensity at 65 kt -- minimal hurricane strength -- that was likely taken as a tentative measure, and Iselle has almost certainly weakened to a tropical storm by now. While some of this could be attributed to the diurnal convective minimum that just finished its cycle over the central Pacific, Iselle is clearly on a sharp decline. Upper-level cirrus debris is shown blowing northeastward away from the center, suggesting some mid-level southwesterly shear may be undercutting the outflow layer.



Figure 1. Latest infrared satellite image of Hurricane Iselle. Image credit: NOAA's Satellite Services Division (SSD).

Given current trends, it is possible Iselle could weaken a little more prior to landfall, especially as it continues to interact with the mountainous terrain on the Big Island. Water vapor imagery shows northwesterly shear not far to the west of the hurricane, which is likely to hasten the weakening process over the next 12-24 hours, in agreement with the global models that also reflect this. A steady weakening trend is expected, and it is possible Iselle could weaken faster than indicated here after it passes the Big Island.

Iselle took a jog south-of-west for a time this evening and slid under the 19N latitude line. While a little uncertain, that motion appears to have stopped, with recent satellite and radar data suggesting a more westerly to north-of-west motion is occurring. Iselle is being steered by a rather weak and distant subtropical ridge to the north, with another, more vigorous ridge located a few hundred miles west of the Hawaiian Islands. This general pattern should still favor a landfall on the southeastern coast of the Big Island, assuming the mountainous topography doesn't induce any possible wobbles around the island, as seemingly occurred with Flossie last year. My forecast track is a little to the south of the latest CPHC prediction, but not by much. It should be noted that the GFS forecasts Iselle to pass just south of the Big Island, a solution which is not impossible. After landfall, Iselle is expected to continue moving west as a weakening system embedded in strong upper-level winds.

Although Iselle appears unlikely to make landfall as a hurricane, widespread power outages are still possible across the Big Island, especially in areas of mountainous terrain, where the winds will be significantly stronger than at ground level. The primary threat will be heavy rain/flash flooding/landslides in areas of higher terrain, along with tree and power line damage. The tornado threat with Iselle appears quite minimal.

Even if the hurricane warning gets taken down, interests in the Big Island should continue to take Iselle very seriously, with that island likely to take the brunt of Iselle's winds. Also, even if Iselle does not make landfall, what's left of the northern and possibly eastern eyewall will affect the southern portion of the coast, leading to sustained tropical storm force winds there, even at ground level. It is possible winds could still exceed hurricane force, especially in gusts, as you enter the higher elevations.

Radar data shows that rainbands and strong winds are already affecting the eastern portion of the Big Island, and the weather will only worsen as Iselle continues westward.

Intensity forecast

Initial 08/08 0600Z 18.9°N 154.4°W 65 kt 75 mph
12 hour 08/08 1800Z 19.3°N 155.7°W 50 kt 60 mph: inland
24 hour 08/09 0600Z 19.4°N 157.3°W 45 kt 50 mph
36 hour 08/09 1800Z 19.6°N 158.5°W 40 kt 45 mph
48 hour 08/10 0600Z 19.8°N 159.8°W 35 kt 40 mph

Track forecast



Figure 2. My forecast track for Iselle.

CPHC storm information

WTPA33 PHFO 080553
TCPCP3

BULLETIN
HURRICANE ISELLE INTERMEDIATE ADVISORY NUMBER 32A
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP092014
800 PM HST THU AUG 07 2014

...ISELLE CHURNING TOWARD THE BIG ISLAND...


SUMMARY OF 800 PM HST...0600 UTC...INFORMATION
----------------------------------------------
LOCATION...18.9N 154.4W
ABOUT 70 MI...115 KM SE OF HILO HAWAII
ABOUT 280 MI...450 KM ESE OF HONOLULU HAWAII
MAXIMUM SUSTAINED WINDS...75 MPH...120 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 15 MPH...24 KM/H
MINIMUM CENTRAL PRESSURE...992 MB...29.30 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES IN WATCHES AND WARNINGS WITH THIS ADVISORY...

NONE.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A HURRICANE WARNING IS IN EFFECT FOR...
* HAWAII COUNTY

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* MAUI COUNTY...INCLUDING THE ISLANDS OF MAUI...MOLOKAI...LANAI...
AND KAHOOLAWE.
* OAHU
* KAUAI COUNTY INCLUDING THE ISLANDS OF KAUAI AND NIIHAU.

A HURRICANE WARNING MEANS THAT HURRICANE CONDITIONS ARE EXPECTED
SOMEWHERE WITHIN THE WARNING AREA. PREPARATIONS TO PROTECT LIFE AND
PROPERTY SHOULD BE RUSHED TO COMPLETION.

A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA WITHIN 36 HOURS.

INTERESTS IN THE NORTHWEST HAWAIIAN ISLANDS SHOULD MONITOR THE
PROGRESS OF ISELLE.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA...PLEASE MONITOR
PRODUCTS ISSUED BY THE NATIONAL WEATHER SERVICE OFFICE IN
HONOLULU HAWAII.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 800 PM HST...0600 UTC...THE CENTER OF HURRICANE ISELLE WAS
LOCATED NEAR LATITUDE 18.9 NORTH...LONGITUDE 154.4 WEST. ISELLE IS
MOVING TOWARD THE WEST NEAR 15 MPH...24 KM/H...AND THIS MOTION IS
EXPECTED TO CONTINUE WITH SOME SLOWING IN FORWARD SPEED OVER THE
NEXT COUPLE OF DAYS. ON THE FORECAST TRACK...ISELLE WILL BE
MOVING ACROSS THE BIG ISLAND TONIGHT...AND PASSING SOUTH OF THE
SMALLER ISLANDS ON FRIDAY AND FRIDAY NIGHT.

MAXIMUM SUSTAINED WINDS ARE ESTIMATED TO BE NEAR 75 MPH...120
KM/H...WITH HIGHER GUSTS. WEAKENING IS FORECAST OVER THE NEXT 48
HOURS...BUT ISELLE COULD STILL BE A HURRICANE WHEN IT MOVES ONSHORE
IN THE NEXT FEW HOURS. ISELLE IS FORECAST TO WEAKEN TO A TROPICAL
STORM OVERNIGHT.

HURRICANE FORCE WINDS EXTEND OUTWARD UP TO 35 MILES...55 KM...FROM
THE CENTER...AND TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 185
MILES...295 KM.

THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 992 MB...29.30 INCHES.


HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM CONDITIONS WILL IMPACT THE BIG ISLAND THROUGH
THE NIGHT...WITH HURRICANE CONDITIONS LIKELY IN SOME AREAS
OVERNIGHT. TROPICAL STORM CONDITIONS ARE EXPECTED OVER MAUI COUNTY
TONIGHT...AND FOR OAHU ON FRIDAY. TROPICAL STORM CONDITIONS ARE
EXPECTED FOR KAUAI COUNTY LATER FRIDAY.

RAINFALL...RAINFALL TOTALS OF 5 TO 8 INCHES...WITH ISOLATED MAXIMUM
AMOUNTS TO 12 INCHES...ARE EXPECTED ALONG THE TRACK OF ISELLE.
THESE RAINS COULD CAUSE LIFE-THREATENING FLASH FLOODS AS WELL AS
ROCK AND MUD SLIDES.

SURF...SWELLS GENERATED BY ISELLE WILL CONTINUE TO BUILD ALONG EAST
FACING SHORES TONIGHT. VERY LARGE...DAMAGING WAVES ARE EXPECTED ALONG
MAINLY EAST AND SOUTH SHORES THROUGH FRIDAY.

STORM SURGE...THE COMBINATION OF STORM SURGE AND THE TIDE WILL CAUSE
NORMALLY DRY AREAS NEAR THE COAST TO BE FLOODED BY RISING WATERS.
THE WATER COULD REACH THE FOLLOWING HEIGHTS ABOVE GROUND IF THE PEAK
SURGE OCCURS AT THE TIME OF HIGH TIDE...

BIG ISLAND WINDWARD AND KAU...1 TO 2 FT

SURGE RELATED FLOODING DEPENDS ON THE RELATIVE TIMING OF THE SURGE
AND THE TIDAL CYCLE...AND CAN VARY GREATLY OVER SHORT DISTANCES.


NEXT ADVISORY
-------------
NEXT COMPLETE ADVISORY...1100 PM HST.

$$

FORECASTER BIRCHARD



Julio

Julio became the fifth major hurricane of the 2014 Pacific hurricane season last night. As of the 0300Z NHC advisory pending the release of the 0900Z advisory, the following information was posted on the hurricane:

Wind: 115 mph, with higher gusts
Location: 17.4°N 139.1°W
Movement: W at 16 mph
Pressure: 966 mb
Category: 3 (Saffir-Simpson Hurricane Wind Scale)

While the eye is still well-defined and cloud free, the central dense overcast has exhibited considerable warming over the last few hours. Satellite estimates are coming down, and Julio has probably weakened a bit, especially considering the marginal water temperatures it is rolling over. Upper-tropospheric outflow remains well-defined, however, signifying an environment of weak vertical shear.



Figure 3. Latest infrared satellite image of Hurricane Julio. Image credit: NOAA's Satellite Services Division (SSD).

The intensity forecast is once again pretty complex. Given the relative lack of banding and the weak wind shear, Julio may be attempting to gain an annular structure similar to what Iselle did in this area a few days ago. While the SHIPS says it's not, I am going to assume that Julio is at least quasi-annular; if true, this should lead to an only gradual, not rapid decay. My forecast shows Julio slowly weakening under continuous 25-26C SSTs and somewhat drier air along the path of the system (although I suspect SHIPS may be overestimating this given Iselle's passage and subsequent moistening of the area). The GFS and ECMWF appear to forecast a period of somewhat increased shear from about 36 to 72 hours, presumably in response to a digging mid- to upper-level trough currently near Alaska, so my forecast shows a noticeably quicker weakening at those times before slowing the rate of weakening thereafter. While Julio is likely to still be of hurricane strength when it nears the Hawaiian Islands in about three days, the models continue to be tightly clustered on a track about 125 to 150 miles north of the archipelago; enough perhaps for some increased surf and locally heavy rains, but little in the way of strong winds.

Julio appears to be moving just a little to the north of the current NHC track, and my forecast is hence a little north of it. The TVCA consensus also shifted a little northward between 18 and 0z, so this appears to be a step in the right direction. However, my forecast track is still a little to the south of that guidance near the end of the period, as the global models generally show more ridging than in previous runs, which is expected to turn Julio more westward as it pulls north of Hawaii early next week. The NAVGEM is currently the southernmost outlier, and shows Julio passing less than 100 miles north of the islands. This solution does not appear likely at this time given the large amplitude cyclonicity already weakening the ridge to the north of the hurricane.

Interests in Hawaii should still monitor the progress of Julio, although I suspect the chances of a direct impact is rather low.

Intensity forecast

Initial 08/08 0300Z 17.4°N 139.1°W 100 kt 115 mph
12 hour 08/08 1200Z 17.7°N 140.6°W 100 kt 115 mph
24 hour 08/09 0000Z 18.3°N 143.2°W 95 kt 110 mph
36 hour 08/09 1200Z 19.4°N 147.2°W 85 kt 100 mph
48 hour 08/10 0000Z 20.8°N 150.1°W 75 kt 85 mph
72 hour 08/11 0000Z 22.8°N 155.0°W 65 kt 75 mph
96 hour 08/12 0000Z 24.5°N 159.6°W 55 kt 65 mph

Track forecast



Figure 4. My forecast track for Julio.

2014 Atlantic hurricane season 2014 Pacific hurricane season Hurricane Iselle Hurricane Julio

Updated: 8:09 AM GMT on August 08, 2014

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Tropical weather analysis - August 7, 2014

By: KoritheMan, 6:23 AM GMT on August 07, 2014

Notice: All forecasts presented here are based upon my own knowledge of atmospheric dynamics. They are created using my knowledge of the various computer models, satellite interpretation, and other tools and parameters. These forecasts, while striving to be accurate, are not intended to supersede predictions by the National Hurricane Center. Always follow NWS protocol and forecasts.

Iselle

Hurricane Iselle continues moving toward Hawaii. As of the latest CPHC advisory package, the following information was posted on the hurricane:

Wind: 90 mph, with higher gusts
Location: 18.0°N 148.4°W
Movement: WNW at 18 mph
Pressure: 982 mb
Category: 1 (Saffir-Simpson Hurricane Wind Scale)

Iselle is a tenacious tropical cyclone. Evening satellite images reveal a resurgence in convection within the CDO and eyewall, when just a few hours go cloud tops were warming. The eye remains ragged and cloud-filled, but still apparent in conventional satellite data. In addition, a 0409Z SSMIS microwave pass still showed a well-defined low- and mid-level eye that was not particularly displaced in the vertical, implying a reduction in environmental wind shear. Satellite estimates would support the intensity of 80 kt assigned by the Central Pacific Hurricane Center. Upper-level outflow is still well-defined for a system over 26C SSTs and embedded in a dry airmass.



Figure 1. Latest infrared satellite image of Hurricane Iselle. Image credit: NOAA's Satellite Services Division (SSD).

Time is running out of time for Iselle to weaken before it makes landfall on the Big Island. Upper air data from Hilo shows about 20 to 25 kt of northerly upper flow at between 300 and 200 mb, which is enough shear to potentially weaken the storm before landfall. However, water vapor imagery and UW-CIMSS synoptic steering analyses indicate that there are two subtropical high pressure cells in the vicinity of Hawaii, one to the west of Iselle and another to the north. The western one appears to be retrograding westward away from the main anticyclone, which should lessen the shear over Hilo. Also, current satellite images do not suggest much in the way of adverse vertical shear, suggesting that Iselle could maintain its 80-kt intensity up to landfall, although there is margin for error -- I'd say about 5 kt up and 5 kt down -- on the intensity spectrum during the next 24 hours. While the GFS and ECMWF suggest an increase in shear as Iselle nears the islands, it will probably not arrive soon enough to appreciably weaken the storm until it begins moving west away from the archipelago; even then, there are indications that the shear may not be as prohibitive as originally thought as Iselle heads farther west after its encounter with Hawaii. On the negative side, although waters do progressively warm as you head west through the islands, upper air data from Hilo and water vapor animations continue to show a significant amount of mid-level dry air in the near-storm environment. This should at least prevent any unexpected last minute intensification.

Iselle continues on a steady west-northwestward track to the south of a broad mid-level ridge to the north. There is a broad region of trailing cyclonicity to the north of Hawaii in association with a large and distant mid- to upper-level trough south of Alaska. The global models forecast this feature to remain in place, which should orient the ridge enough to allow for a continued west-northwestward motion toward the Big Island. Landfall is expected in about 24-30 hours, which would be Thursday afternoon or early Thursday evening local time (the times I have used below on my track forecast represent eastern time). The guidance continues to be surprisingly stable, and my forecast track is similar to the current CPHC prediction, and only a tad farther south; this is also to the south of the latest TVCA model consensus.

A hurricane warning is now in effect for the Big Island. This is the first time a hurricane warning has been issued for Hawaii since Hurricane Fernanda threatened the island chain in 1993. A tropical storm warning is also in effect for Maui County, including the islands of Maui, Molokai, Lanai, and Kahoolawe; it is also in effect for Oahu. Finally, a tropical storm watch is also in effect for Kauai. It is still a little too soon to say how strong Iselle will be, as well as whether it will jog north or south of the Big Island. The mountains on Hawaii County are rather steep, and I do not believe the global models have a good handle on this geographic variable. If no change in track occurs as a result of interaction with the mountains, to my knowledge Iselle would be the first hurricane landfall on the Big Island since records began.

Heavy rainfall, flash flooding and mudslides are likely across the islands, especially in areas of higher terrain. In addition, sustained hurricane-force winds appear liable to effect the Big Island at this point, and these winds could be significantly stronger in areas of elevated terrain. Widespread tree and power line damage appears likely on the islands, especially in Hawaii County, which at this point appears to be the target for the brunt of the storm. Regardless of the exact trajectory, the entire island chain is likely to experience a prolonged period of tropical storm force winds, again with the rains and winds being enhanced in higher elevations.

Intensity forecast

Initial 08/07 0300Z 18.0N 148.4W 80 kt 90 mph
12 hour 08/07 1200Z 18.3°N 150.0°W 80 kt 90 mph
24 hour 08/08 0000Z 18.8°N 153.3°W 80 kt 90 mph: near Big Island
36 hour 08/08 1200Z 19.5°N 155.9°W 60 kt 70 mph: just offshore Big Island
48 hour 08/09 0000Z 20.2°N 159.7°W 45 kt 50 mph

Track forecast



Figure 2. My forecast track for Iselle.

CPHC storm information

WTPA33 PHFO 070241
TCPCP3

BULLETIN
HURRICANE ISELLE ADVISORY NUMBER 28
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP092014
500 PM HST WED AUG 06 2014

...ISELLE REMAINS A DANGEROUS HURRICANE AS IT APPROACHES HAWAII...


SUMMARY OF 500 PM HST...0300 UTC...INFORMATION
----------------------------------------------
LOCATION...17.7N 147.5W
ABOUT 515 MI...830 KM ESE OF HILO HAWAII
ABOUT 720 MI...1160 KM ESE OF HONOLULU HAWAII
MAXIMUM SUSTAINED WINDS...90 MPH...150 KM/H
PRESENT MOVEMENT...WNW OR 285 DEGREES AT 18 MPH...30 KM/H
MINIMUM CENTRAL PRESSURE...982 MB...29.00 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES IN WATCHES AND WARNINGS WITH THIS ADVISORY...

A TROPICAL STORM WARNING HAS BEEN ISSUED FOR OAHU AND A TROPICAL
STORM WATCH HAS BEEN ISSUED FOR KAUAI COUNTY.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A HURRICANE WARNING IS IN EFFECT FOR...
* HAWAII COUNTY

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* MAUI COUNTY...INCLUDING THE ISLANDS OF MAUI...MOLOKAI...LANAI...
AND KAHOOLAWE.
* OAHU

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* KAUAI COUNTY INCLUDING THE ISLANDS OF KAUAI AND NIIHAU.

A HURRICANE WARNING MEANS THAT HURRICANE CONDITIONS ARE EXPECTED
SOMEWHERE WITHIN THE WARNING AREA. PREPARATIONS TO PROTECT LIFE AND
PROPERTY SHOULD BE RUSHED TO COMPLETION. A WARNING IS TYPICALLY
ISSUED 36 HOURS BEFORE THE ANTICIPATED FIRST OCCURRENCE OF TROPICAL
STORM FORCE WINDS...CONDITIONS THAT MAKE OUTSIDE PREPARATIONS
DIFFICULT OR DANGEROUS.

A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA WITHIN 36 HOURS.

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE SOMEWHERE WITHIN THE WATCH AREA WITHIN THE NEXT 48 HOURS.

INTERESTS IN THE NORTHWEST HAWAIIAN ISLANDS SHOULD MONITOR THE
PROGRESS OF ISELLE.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 500 PM HST...0300 UTC...THE EYE OF HURRICANE ISELLE WAS LOCATED
NEAR LATITUDE 17.7 NORTH...LONGITUDE 147.5 WEST. ISELLE IS MOVING
TOWARD THE WEST-NORTHWEST NEAR 18 MPH...30 KM/H...AND THIS MOTION IS
EXPECTED TO CONTINUE FOR THE NEXT 48 HOURS. ON THE FORECAST TRACK...
THE CENTER OF ISELLE IS EXPECTED TO PASS VERY NEAR OR OVER THE BIG
ISLAND THURSDAY NIGHT...AND PASS JUST SOUTH OF THE SMALLER ISLANDS
FRIDAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 90 MPH...150 KM/H...WITH HIGHER
GUSTS. SOME WEAKENING IS FORECAST DURING THE NEXT 48 HOURS.
HOWEVER...ISELLE IS STILL EXPECTED TO BE NEAR HURRICANE STRENGTH AS
IT PASSES NEAR OR OVER THE BIG ISLAND.

HURRICANE FORCE WINDS EXTEND OUTWARD UP TO 45 MILES...75 KM...FROM
THE CENTER...AND TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 140
MILES...220 KM.

THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 982 MB...29.00 INCHES.


HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM CONDITIONS ARE EXPECTED ON THE BIG ISLAND OF
HAWAII THURSDAY...WITH HURRICANE CONDITIONS EXPECTED THURSDAY
NIGHT. TROPICAL STORM CONDITIONS ARE EXPECTED FOR PORTIONS OF MAUI
COUNTY THURSDAY NIGHT...AND FOR OAHU LATE THURSDAY NIGHT AND FRIDAY.
TROPICAL STORM CONDITIONS ARE POSSIBLE FOR KAUAI COUNTY ON FRIDAY.

SURF...SWELLS GENERATED BY ISELLE WILL CONTINUE TO BUILD ALONG EAST
FACING SHORES TONIGHT. VERY LARGE...DAMAGING SURF IS EXPECTED ALONG
MAINLY EAST AND SOUTH SHORES STARTING LATE TONIGHT OR THURSDAY.

RAINFALL...RAINFALL TOTALS OF 5 TO 8 INCHES...WITH ISOLATED MAXIMUM
AMOUNTS TO 12 INCHES...ARE EXPECTED ALONG THE TRACK OF ISELLE. THESE
RAINS COULD CAUSE LIFE-THREATENING FLASH FLOODS AS WELL AS ROCK AND
MUD SLIDES.

STORM SURGE...THE COMBINATION OF A DANGEROUS STORM SURGE AND THE
TIDE WILL CAUSE NORMALLY DRY AREAS NEAR THE COAST TO BE FLOODED BY
RISING WATERS. THE WATER COULD REACH THE FOLLOWING HEIGHTS ABOVE
GROUND IF THE PEAK SURGE OCCURS AT THE TIME OF HIGH TIDE...

BIG ISLAND WINDWARD AND KAU...1 TO 3 FT

THE HIGHEST WATER WILL OCCUR ALONG THE IMMEDIATE COAST IN AREAS OF
ONSHORE FLOW. THE SURGE WILL BE ACCOMPANIED BY LARGE AND DAMAGING
WAVES. SURGE RELATED FLOODING DEPENDS ON THE RELATIVE TIMING OF THE
SURGE AND THE TIDAL CYCLE...AND CAN VARY GREATLY OVER SHORT
DISTANCES.


NEXT ADVISORY
-------------
NEXT INTERMEDIATE ADVISORY...800 PM HST.
NEXT COMPLETE ADVISORY...1100 PM HST.

$$
FORECASTER R BALLARD



Julio

Hurricane Julio is moving westward closely behind Iselle. As of the 0300Z NHC advisory, the following information was posted on the hurricane:

Wind: 85 mph, with higher gusts
Location: 16.4°N 133.2°W
Movement: WNW at 16 mph
Pressure: 985 mb
Category: 1 (Saffir-Simpson Hurricane Wind Scale)

There hasn't been much change to Julio's cloud pattern since the release of the 3Z NHC advisory. Deep convection surrounds the small and ragged eye, although cloud tops have recently warmed a bit in the northern eyewall.



Figure 3. Latest infrared satellite image of Hurricane Julio. Image credit: NOAA's Satellite Services Division (SSD).

Although Julio is still over waters perhaps just warm enough (upper 26C to lower 27C) to support additional intensification, any such opportunity will have to be seized overnight. While the cold wake from Iselle so far doesn't appear as pronounced as I thought it would, the SHIPS SST integration and more objective SST interpretation for the area suggest that waters will remain in the 25 to 26C range along the forecast track of Julio throughout the forecast period. Combined with an increasingly marginal thermodynamic environment, a weakening trend seems inevitable beyond about 24 hours. Having said that, the environmental conditions Julio will be encountering aren't too dissimilar to the ones Iselle has been traversing over the last few days, and hurricanes over marginal waters/thermodynamics often surprise. The weakening is expected to be gradual, not rapid, even as Julio approaches Hawaii this weekend. The GFS/ECMWF show a possible increase in westerly shear over Julio by days four and five, but they are not as enthusiastic about this as they have been. With Iselle expected to also encounter less hostile conditions, and the digging mid- to upper-level trough gradually lifting out over the next few days, I do not anticipate shear to put the brakes on Julio; instead, the marginal thermodynamics are likely to weaken it.

There's not much new I can say pertaining to Julio's track. The cyclone also appears to be fairly steady-state in terms of its track predictability, with the same general pattern expected to influence Julio that's influencing Iselle. The aforementioned trough is forecast to dig southward over the next few days, eroding the ridge to the north of Julio as it nears the Hawaiian Islands in about four days. This should cause a gentle northwestward bend of the track around that time, allowing Julio to pass safely north of the islands. While some of the outlying guidance suggests a track farther south much closer to Hawaii, the model consensus remains entrenched on a path about 100 miles north of those islands, and my forecast is fairly similar to the latest National Hurricane Center prediction in reflecting that scenario instead. I'm not completely confident that Julio will miss, however, and interests in Hawaii should continue to monitor the progress of Julio carefully over the next few days. It's more likely than not that it misses the islands, but I would say there is about a 30% that it doesn't.

Also, even though my own track, the model consensus, and the National Hurricane Center forecast track show Julio passing well north of the islands, it would still be far enough north that the southerly influx of moist air south of the cyclone center may allow for heavy rainfall along the island chain, particularly in more mountainous areas.

Intensity forecast

Initial 08/07 0300Z 16.4°N 133.2°W 75 kt 85 mph
12 hour 08/07 1200Z 16.7°N 135.0°W 80 kt 90 mph
24 hour 08/08 0000Z 17.2°N 138.9°W 80 kt 90 mph
36 hour 08/08 1200Z 17.7°N 140.7°W 75 kt 85 mph
48 hour 08/09 0000Z 18.7°N 144.7°W 70 kt 80 mph
72 hour 08/10 0000Z 20.3°N 150.2°W 65 kt 75 mph
96 hour 08/11 0000Z 22.1°N 155.0°W 55 kt 65 mph
120 hour 08/12 0000Z 25.2°N 159.7°W 50 kt 60 mph

Track forecast



Figure 4. My forecast track for Julio.

2014 Atlantic hurricane season 2014 Pacific hurricane season Hurricane Iselle Hurricane Julio

Updated: 6:32 AM GMT on August 07, 2014

Permalink

Tropical weather analysis - August 6, 2014

By: KoritheMan, 6:25 AM GMT on August 06, 2014

Notice: All forecasts presented here are based upon my own knowledge of atmospheric dynamics. They are created using my knowledge of the various computer models, satellite interpretation, and other tools and parameters. These forecasts, while striving to be accurate, are not intended to supersede predictions by the National Hurricane Center. Always follow NWS protocol and forecasts.

Bertha

Tropical Storm Bertha is accelerating across the northwestern Atlantic. As of the 0300Z NHC advisory bulletin, the following information was posted on Bertha:

Wind: 50 mph, with higher gusts
Location: 37.5°N 68.1°W
Movement: NE at 23 mph
Pressure: 1007 mb

Shear has increased significantly over Bertha from the west ahead of an approaching mid-latitude frontal system. Consequently, the low-level center is exposed to the west of the convection, which is still rather vigorous. Thermal cross sections over the cyclone do not currently show much in the way of tropospheric cooling, and given the impressive burst of convection seen on satellite imagery, Bertha obviously hangs on as a tropical cyclone for the now.



Figure 1. Latest infrared satellite image of Tropical Storm Bertha. Image credit: NOAA's Satellite Services Division (SSD).

While Bertha has run out of time to intensify tropically, the post-tropical iteration of Bertha will likely be slow to weaken as it gets infused with baroclinic energy attendant to the aforementioned trough and associated frontal zone. Since Bertha still doesn't appear to be on the "cold" side of the front, the current convection is more likely due to upper divergence from the trough and not raw baroclinic forcing. Most of the models show Bertha weakening as an extratropical cyclone after about 48 hours, and my forecast will reflect that. There is some disagreement among the guidance as to whether Bertha will dissolve itself over western Europe in 5 - 6 days, or if it will instead become absorbed by a stronger extratropical low over the North Atlantic. The ECMWF and UKMET maintain Bertha as a weak but distinct entity from that system, while the remainder of the guidance except the CMC (which shows a binary interaction that ultimately ends with Bertha assimilating/dominating the low) indicate that Bertha will become absorbed by the low. However, there is still enough uncertainty in the specifics of this evolution that I will continue to carry a 5-day forecast point.

There is not much to say regarding the track of Bertha. The cyclone is well-embedded in the high latitude westerlies, with recent satellite data suggesting that the tropical storm may even be moving a little faster, possibly in what will no doubt be an unsuccessful effort to catch up with the convection in the face of harsh environmental wind shear. Bertha is forecast to continue accelerating along the western and northern portion of the Atlantic subtropical ridge, not threatening any land areas aside from perhaps some local impacts in extreme southeastern Newfoundland.

Intensity forecast

Initial 08/06 0300Z 37.5°N 68.1°W 45 kt 50 mph
12 hour 08/06 1200Z 40.4°N 59.0°W 45 kt 50 mph
24 hour 08/07 0000Z 43.8°N 54.8°W 45 kt 50 mph: extratropical
36 hour 08/07 1200Z 45.3°N 50.7°W 45 kt 50 mph: extratropical
48 hour 08/08 0000Z 47.2°N 45.0°W 45 kt 50 mph: extratropical
72 hour 08/09 0000Z 48.1°N 34.3°W 40 kt 45 mph: extratropical
96 hour 08/10 0000Z 48.4°N 20.7°W 35 kt 40 mph: extratropical
120 hour 08/11 0000Z 48.7°N 10.0°W 30 kt 35 mph: extratropical

Track forecast



Figure 2. My forecast track for Bertha.



Iselle

Iselle continues moving westward across the central Pacific as a Category 2 hurricane. As of the 0600Z CPHC intermediate advisory, the following information was posted on the storm:

Wind: 100 mph, with higher gusts
Location: 16.8N 142.3W
Movement: WNW at 13 mph
Pressure: 974 mb
Category: 2 (Saffir-Simpson Hurricane Wind Scale)

Iselle's cloud pattern continues to steadily deteriorate, with little evidence of deep convection to the south of the ragged, elongating, and cloud-filled eye. The fragmented eyewall convection remains fairly deep in the northern semicircle, however, with the relatively disorganized internal structure likely the result of very dry air becoming entrained into the southern quadrant of the hurricane, and perhaps a bit of southerly to south-southwesterly vertical wind shear.



Figure 3. Latest infrared satellite image of Hurricane Iselle. Image credit: NOAA's Satellite Services Division (SSD).

The shear is forecast to decrease over the next 24 hours as forecast by the models and as apparent on water vapor imagery. The result should be a slower rate of weakening beyond that time, just in time for Iselle to approach Hawaii. Most of the intensity guidance also supports a slower rate of decay as the cyclone approaches the Hawaiian Islands, although the LGEM/SHIPS continue to anticipate an initial weakening that appears a little premature and expedited, thus giving those models a pronounced low bias throughout the forecast period. I should note that even with the expected decrease in shear, water vapor and CIMSS TPW data reveal an enormous amount of dry air to the west of the cyclone along the projected path; even without the shear, that's going to leave a mark. My forecast shows Iselle moving over the Big Island as a 50 kt tropical storm late Thursday evening (eastern time; local time would still be around late afternoon or early evening), but it is of course possible that the cyclone could be a little weaker than this as i moves through the islands, a symptom common of westward-moving hurricanes approaching the island chain. The ECMWF shows somewhat stronger northwesterly shear afflicting Iselle on the backside of an upper trough as the system approaches Hawaii, so the system could be a little weaker than advertised here if that scenario pans out.

Iselle appears to be following the forecast track from the NHC/CPHC rather well, and the track has been surprisingly stable. The majority of the models still take the cyclone near or over the Big Island in about 48 hours. The typically reliable TVCA consensus continues to show Iselle making a landfall on the Big Island, and my forecast goes along with that, agreeing most strongly with the 12z NAVGEM, but is a little to the north of that model and very close to the consensus. If there will be any additional track shifts before the system reaches the islands, I imagine they will be southward ones, as the GFS and ECMWF show that ridging, not troughing, will be liable to control the motion of Iselle as it approaches Hawaii.

A tropical storm watch is in effect for the Big Island. Since the average lead time for a tropical storm warning in the central Pacific is roughly 36 hours, this could be upgraded to a tropical storm warning later today (Wednesday). Sustained hurricane-force winds currently appear unlikely, but Hawaii is a rather mountainous archipelago, and winds will be significantly higher in areas of elevated terrain.

Interests in the Hawaiian Islands should continue to monitor the progress of Iselle. A tropical cyclone is a not point, and significant impacts extend well away from the center.

A hurricane hunter aircraft is currently investigating Iselle, and data from this mission should provide a more in situ assessment of the cyclone's structure and intensity. Dropsondes from this flight will be dropped into the environment of Iselle, helping to boost model accuracy.

Intensity forecast

Initial 08/06 0300Z 16.8°N 141.6°W 85 kt 100 mph
12 hour 08/06 1200Z 17.4°N 143.8°W 80 kt 90 mph
24 hour 08/07 0000Z 18.2°N 147.4°W 70 kt 80 mph
36 hour 08/07 1200Z 18.8°N 150.7°W 60 kt 70 mph
48 hour 08/08 0000Z 19.5°N 154.3°W 50 kt 60 mph: near Big Island
72 hour 08/09 0000Z 20.5°N 159.5°W 40 kt 45 mph

Track forecast



Figure 4. My forecast track for Iselle.

CPHC storm information

WTPA33 PHFO 060252
TCPCP3

BULLETIN
HURRICANE ISELLE ADVISORY NUMBER 23
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP092014
500 PM HST TUE AUG 05 2014

...ISELLE CONTINUES TO WEAKEN...BUT STILL MOVING TOWARD HAWAII...


SUMMARY OF 500 PM HST...0300 UTC...INFORMATION
----------------------------------------------
LOCATION...16.8N 141.6W
ABOUT 905 MI...1460 KM E OF HILO HAWAII
MAXIMUM SUSTAINED WINDS...100 MPH...155 KM/H
PRESENT MOVEMENT...WNW OR 295 DEGREES AT 13 MPH...20 KM/H
MINIMUM CENTRAL PRESSURE...977 MB...28.85 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES IN WATCHES AND WARNINGS WITH THIS ADVISORY...

NONE.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* HAWAII COUNTY

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA WITHIN 48 HOURS.

INTERESTS ELSEWHERE IN THE MAIN HAWAIIAN ISLANDS SHOULD MONITOR THE
PROGRESS OF ISELLE. WATCHES MAY BE REQUIRED FOR ADDITIONAL ISLANDS
TONIGHT OR EARLY WEDNESDAY.

FOR STORM INFORMATION SPECIFIC FOR YOUR AREA...PLEASE MONITOR
PRODUCTS ISSUED BY THE NATIONAL WEATHER SERVICE OFFICE IN HONOLULU.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 500 PM HST...0300 UTC...THE CENTER OF HURRICANE ISELLE WAS
LOCATED NEAR LATITUDE 16.8 NORTH...LONGITUDE 141.6 WEST. ISELLE IS
MOVING TOWARD THE WEST-NORTHWEST NEAR 13 MPH...20 KM/H. THIS
MOTION IS EXPECTED TO CONTINUE DURING THE NEXT 48 HOURS...WITH SOME
INCREASE IN FORWARD SPEED AS ISELLE APPROACHES HAWAII. ON THE
FORECAST TRACK...THE CENTER OF ISELLE WILL BE APPROACHING THE
BIG ISLAND THURSDAY AFTERNOON.

MAXIMUM SUSTAINED WINDS ARE NEAR 100 MPH...155 KM/H...WITH HIGHER
GUSTS. ADDITIONAL WEAKENING IS FORECAST DURING THE NEXT 48 HOURS...
AND ISELLE IS EXPECTED TO BECOME A TROPICAL STORM BY THURSDAY.

HURRICANE FORCE WINDS EXTEND OUTWARD UP TO 30 MILES...45 KM...FROM
THE CENTER...AND TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 115
MILES...185 KM.

THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 977 MB...28.85 INCHES.


HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM CONDITIONS ARE POSSIBLE ON THE BIG ISLAND OF
HAWAII ON THURSDAY.

SURF...SWELLS GENERATED BY ISELLE ARE EXPECTED TO REACH THE MAIN
HAWAIIAN ISLANDS LATE TUESDAY THROUGH WEDNESDAY...AND POSSIBLY
BECOMING DAMAGING BY THURSDAY.

RAINFALL...HEAVY RAINS ASSOCIATED WITH ISELLE WILL REACH THE BIG
ISLAND THURSDAY AND SPREAD TO THE REMAINDER OF THE STATE THURSDAY
NIGHT AND FRIDAY. THESE RAINS COULD CAUSE LIFE-THREATENING FLASH
FLOODS AND MUD SLIDES.


NEXT ADVISORY
-------------
NEXT INTERMEDIATE ADVISORY...800 PM HST.
NEXT COMPLETE ADVISORY...1100 PM HST.

$$
FORECASTER BIRCHARD/R BALLARD



Julio

Tropical Storm Julio is slowly intensifying. As of the 0300Z NHC advisory, the following information was posted on the storm:

Wind: 65 mph, with higher gusts
Location: 14.4°N 127.5°W
Movement: WNW at 15 mph
Pressure: 994 mb

Julio appears rather impressive this evening. Evening microwave data indicates a robust low- to mid-level eye, with periodic manifestations of this on conventional satellite data. Upper-level outflow is well-defined in all quadrants, suggesting little environmental shear.



Figure 5. Latest infrared satellite image of Tropical Storm Julio. Image credit: NOAA's Satellite Services Division (SSD).

The intensity forecast for Julio this evening is a puzzling one. As I noted above, the satellite presentation continues to improve, with deep convection attempting to wrap around the warm spot seen in satellite imagery. In addition, a mid-level eye as robust as the one I'm seeing on microwave data often presages rapid intensification. In fact, the SHIPS rapid intensification parameter has climbed by over 10% between 18 and 0z, and now shows a 33% chance of a 25-kt increase in wind speed during the next 24 hours, and a 27% chance of a 30-kt increase during the same time period; I would not be surprised if this escalates even quicker at the 6z cycle. The biggest factor arguing against a rapid intensification episode -- at least one persisting with any degree of longevity -- is time. The SHIPS file and other, more objective SST data, indicate that Julio will reach waters dropping below 27C just after 24 hours; these waters are more than likely partially attributable to the cold water upwelling left behind by Hurricane Iselle. A gradual weakening trend is anticipated beyond 36 hours as Julio encounters marginal waters and dry air associated with those waters. There is also some suggestion that westerly shear may increase a little over Julio at day five, but there is enough uncertainty in the proximity of those winds in relation to the cyclone to not warrant inclusion into my forecast at this time.

Julio remains south of a deep-layer ridge, with water vapor imagery showing a broad mid- to upper-level trough not far off the California coast is eroding the ridge and preventing a more westward component of motion. This evolution was expected, and Julio is so far not showing much deviation from the model guidance or the NHC. A continued west-northwest motion is forecast until near the end of the period, when most of the global and dynamical models show a turn to the northwest as an unusually deep trough digs southward to the north of the Hawaiian Islands and breaks the subtropical ridge. While Julio will probably still pass relatively close to Hawaii, the primary trend in the models the last few days has been for the storm to pass north of the islands. My own forecast has been adjusted accordingly. This prediction remains similar to but a little south of the current National Hurricane Center prediction due to current storm motion trends, but ends up pretty much on top it by day five.

Interests in Hawaii should still carefully monitor Julio's progress over the next several days; much of the islands are still well within the cone of uncertainty.

Intensity forecast

Initial 08/06 0300Z 14.4°N 127.5°W 55 kt 65 mph
12 hour 08/06 1200Z 14.7°N 129.8°W 65 kt 75 mph
24 hour 08/07 0000Z 15.3°N 132.4°W 75 kt 85 mph
36 hour 08/07 1200Z 15.8°N 135.6°W 80 kt 90 mph
48 hour 08/08 0000Z 16.5°N 138.6°W 75 kt 85 mph
72 hour 08/09 0000Z 17.6°N 144.0°W 70 kt 80 mph
96 hour 08/10 0000Z 19.4°N 150.0°W 60 kt 70 mph
120 hour 08/11 0000Z 21.8°N 154.8°W 50 kt 60 mph

Track forecast



Figure 6. My forecast track for Julio.

2014 Atlantic hurricane season 2014 Pacific hurricane season Tropical Storm Bertha Hurricane Iselle Tropical Storm Julio

Updated: 6:36 AM GMT on August 06, 2014

Permalink

Tropical weather analysis - August 4, 2014

By: KoritheMan, 9:56 AM GMT on August 04, 2014

Bertha

Bertha is intensifying, and is just under hurricane strength as of the 0900Z NHC advisory:

Wind: 70 mph, with higher gusts
Location: 26.1°N 73.6°W
Movement: N at 16 mph
Pressure: 999 mb

While the satellite presentation is not as impressive as some 60 kt tropical storms I've seen, a NOAA aircraft has recently found surface data complimenting an upgrade to 60 kt at synoptic time. Rapid strengthening does not appear imminent even though the shear is lessening, as the central convection has been pulsating a bit, and the central pressure is still a little high.



Figure 1. Latest infrared satellite image of Tropical Storm Bertha. Image credit: NOAA's Satellite Services Division (SSD).

As previously mentioned, environmental wind shear appears to be decreasing over Bertha, with evidence that the upper flow is transitioning more to a southwesterly dominance, consistent with the approach of an amplified mid- to upper-level trough over the eastern United States. Most of the guidance still makes Bertha a hurricane, and my forecast will call for the cyclone to achieve that designation in about 24 hours, although it could occur a little sooner, as the GFS/ECMWF develop a small 200 mb ridge over the storm during the next 12-24 hours as it begins to enter the westerlies. By about 48 hours, southwesterly to westerly shear is forecast to increase significantly over Bertha; combined with rapidly cooling waters north of the Gulf Stream and interaction with the aforementioned trough, the end result should be extratropical transition over the north Atlantic as Bertha accelerates northeastward. It is possible that Bertha could become extratropical a little sooner than I have indicated below. It's interesting to note that both the GFS and ECMWF wind shear fields show a cold low currently over the central Atlantic moving westward and catching up with Bertha during the next couple of days. The northeasterly flow ahead of the low could combine with the southwesterly flow ahead of the western Atlantic trough and increase upper divergence over the cyclone. For that reason, and also because the models do not show Bertha getting appreciably detached from the trough for awhile, the post-tropical decay process will likely be less than what would normally be expected. It is still possible Bertha could get stronger than shown below before beginning extratropical transition.

Bertha has made the anticipated turn to the north as the cyclone rounds the western extension of the subtropical ridge. While some of the guidance still shows some binary interaction with a weak disturbance over the Bahamas that could theoretically induce a more westward component somewhat closer to the mid-Atlantic coast, there is no sign of organization with that particular system; in fact, the convection has weakened considerably, with much of the activity now located over the Gulf of Mexico. Bertha is forecast to accelerate northeastward over the next 24 hours, with a gentle eastward turn seen at the end of the forecast period. My forecast track is close to the National Hurricane Center prediction, and the model consensus TVCN. It is also left of my previous forecast at days four and five.

Intensity forecast

Initial 08/04 0600Z 25.4°N 73.5°W 60 kt 70 mph
12 hour 08/04 1800Z 27.4°N 74.3°W 60 kt 70 mph
24 hour 08/05 0600Z 30.3°N 73.3°W 65 kt 75 mph
36 hour 08/05 1800Z 34.3°N 70.8°W 70 kt 80 mph
48 hour 08/06 0600Z 38.8°N 68.6°W 70 kt 80 mph
72 hour 08/07 0600Z 41.2°N 60.0°W 65 kt 75 mph
96 hour 08/08 0600Z 46.3°N 48.8°W 55 kt 65 mph: extratropical
120 hour 08/09 0600Z 49.5°N 37.6°W 45 kt 50 mph: extratropical

Track forecast



Figure 2. My forecast track for Bertha. Note that the forecast track (and thus the initial position) was made using the 6z data, but the blog itself took me longer to finish than that. I apologize for the discrepancies.


Iselle

Major Hurricane Iselle continues moving westward across the eastern Pacific. As of the 0900Z NHC position, the following information was posted on the hurricane:

Wind: 125 mph, with higher gusts
Location: 16.0°N 135.6°W
Movement: W at 9 mph
Pressure: 958 mb
Category: 3 (Saffir-Simpson Hurricane Wind Scale)

The cloud pattern remains impressive since the release of the special advisory upgrading the winds to 110 kt at 6z. The eye is large and cloud free, and there is deep convection in the eyewall spiraling around the eye. Dvorak numbers are between 6.0 and 5.5 from CIMSS ADT and SAB, suggesting that the National Hurricane Center's currently assigned 110 kt intensity remains a good presumption. Upper-level outflow is well-defined in all quadrants, signifying little to no environmental wind shear.



Figure 3. Latest infrared satellite image of Hurricane Iselle. Image credit: NOAA's Satellite Services Division (SSD).

Iselle's intensity forecast is complex. The hurricane has been steadily assimilating annular characteristics for the last 24 hours, with little in the way of convective banding radiating outward from the center at this point. In addition, there is no evidence of any large-scale vertical shear affecting the hurricane, nor is there a lot of eastward-moving cirrus (westerly shear) downstream from its current position on water vapor imagery. As long as the shear remains as low as it is, the marginal thermodynamics or inner core fluctuations will be the primary contributors to the cyclone's intensity. Objective areal sea surface temperature analyses indicate that the SHIPS SST integration may be about a half a degree Celsius too cold, suggesting that Iselle may have more thermal energy to work with, at least in the short-term. A very slow and uncertain weakening is forecast from this point through the end of the forecast period. I say uncertain because annular hurricanes have a notorious tendency to remain stronger than advertised by the models or conventional meteorological knowledge; in fact, I am mostly advertising the initial weakening due to the likelihood of hard-to-time eyewall replacement cycles, and not because of any abrupt change in atmospheric parameters surrounding the hurricane. Later in the period, westerly shear is forecast to increase a little in association with a digging trough, so the cyclone is forecast to begin quickly weakening at those times as the shear helps inject dry air into the circulation as the system approaches Hawaii.

Iselle continues moving pretty much due west this morning. This general motion is likely to continue for at least the next 36 hours. After about that time, most of the guidance forecasts a west-northwestward motion to begin as a broad mid- to upper-level trough digs southward along 150W and erodes the subtropical ridge over Hawaii. While the models are in good agreement on this trough eventually lifting out, a second, much stronger impulse is forecast to dive southward from Alaska and reinforce the cyclonic flow in that area, which appears to be why the models continue moving the storm toward Hawaii instead of moving it westward to the south of the archipelago. My forecast track is similar to the latest ECMWF prediction, and takes Iselle over the Big Island Friday morning. Since the threat to Hawaii is still about four days away, additional northward or southward adjustments are entirely possible over the next few days. Residents there should continue to be very attentive to this situation.

Intensity forecast

Initial 08/04 0600Z 16.0°N 135.2°W 110 kt 125 mph
12 hour 08/04 1800Z 16.0°N 136.6°W 110 kt 125 mph
24 hour 08/05 0600Z 16.0°N 138.1°W 105 kt 120 mph
36 hour 08/05 1800Z 16.1°N 140.2°W 100 kt 115 mph
48 hour 08/06 0600Z 16.7°N 143.5°W 90 kt 105 mph
72 hour 08/07 0600Z 17.8°N 148.8°W 80 kt 90 mph
96 hour 08/08 0600Z 19.6°N 154.9°W 55 kt 65 mph: near Big Island
120 hour 08/09 0600Z 21.7°N 159.7°W 40 kt 45 mph

Track forecast



Figure 4. My forecast track for Iselle. Like with Bertha, my forecast track was made using the 6z coordinates, so there will naturally be some discrepancies with the synoptic data from 9Z



Julio

Tropical Storm Julio recently formed over the Pacific several hundred miles east of Iselle. As of the 0300Z NHC advisory, the following information was posted on Julio:

Wind: 40 mph, with higher gusts
Location: 13.4°N 118.4°W
Movement: W at 13 mph
Pressure: 1004 mb

The cloud pattern is still not terribly well-organized, but recent microwave and satellite data suggest that the low-level center could be a little more involved with the convection than it has been. A 0545Z ASCAT pass showed a slew of believable 30 kt vectors within the deep convection west of the center, which was the basis for an upgrade from the National Hurricane Center at 9z. There are currently little in the way of banding features, and upper-tropospheric outflow is limited to the western semicircle due to persistent easterly shear associated with a distant mid- to upper-level ridge.



Figure 5. Latest infrared satellite image of Tropical Storm Julio. Image credit: NOAA's Satellite Services Division (SSD).

The models show the shear slowly decreasing during the next 24-36 hours, so a more rapid pace of strengthening is shown then. I expect Julio to become a hurricane in about 48 hours, although if the shear eases up sooner it could occur in as little as 36 hours. Subsequently, a period of rapid intensification is certainly possible given the very warm sea surface temperatures and the deep upper ridge the GFS and ECMWF predict will build over the top of the storm. However, it is best to err on the side of conservatism until this becomes more certain, and my forecast does not explicitly indicate the traditional rate of rapid intensification for now. It is, however, a fair bit higher than the current NHC prediction which only takes Julio up to 80 kt. It is close to a blend of the GFDL, which brings Julio up to 85 kt, and the SHIPS, which brings Julio just shy of major hurricane intensity. The situation we have here is a little analogous to the one that allowed Iselle to become a major hurricane, and it is a distinct scenario that her predecessor could follow in her wake. Perhaps unnervingly, the GFS/ECMWF show a decently favorable upper wind configuration even as Julio begins to approach Hawaii beyond day five; this is not typical, as Hawaii is normally protected by shear from the mid-oceanic trough. If Julio ends up following the track of the models and passing near or over Hawaii, it could by far be stronger of the two storms, likely still at hurricane intensity at the time of closest approach. Some weakening still seems likely at days four and five as Julio approaches a cold water wake left behind by Iselle.

Julio is embedded within the deep easterlies south of a strong low- to mid-level ridge. The models are in good agreement that Julio should move generally westward over the next couple of days to the south of this ridge, with a few of the models even suggesting a possible south-of-west motion for more than just a brief duration. When the cyclone gets west of 125W, a turn more toward the west-northwest is likely to commence as Iselle and a strong mid- to upper-level trough along 150W weaken the ridge in the vicinity of the Hawaiian Islands. There is some discrepancy in regards to the timing of the west-northwestward turn, with the ECMWF indicating a more gradual turn and keeping Julio just south of the islands, while the GFS shows a quicker turn into the trough, and consequently a track farther north and much closer to the islands. While there's currently no hard evidence to favor one scenario over the other, if Iselle doesn't weaken too significantly, it may be able to keep a deep enough weakness in the ridge to induce a motion closer to what the GFS suggests, My forecast track attempts to blend both models but is biased a little closer to the GFS solution, at least for now. I'll have to look into making possible adjustments to the forecast track in either direction over the next few days.

Once again, I want to emphasize that Julio could be a rare hurricane for Hawaii if the current forecast tracks in the models pan out, and interests there should monitor Julio very carefully over the next 7 days.

Intensity forecast

Initial 08/04 0900Z 13.4°N 118.4°W 35 kt 40 mph
12 hour 08/04 1800Z 13.3°N 120.0°W 40 kt 45 mph
24 hour 08/05 0600Z 13.4°N 122.3°W 45 kt 50 mph
36 hour 08/05 1800Z 13.7°N 125.3°W 55 kt 65 mph
48 hour 08/06 0600Z 14.1°N 128.4°W 70 kt 80 mph
72 hour 08/07 0600Z 14.6°N 133.6°W 90 kt 105 mph
96 hour 08/08 0600Z 15.3°N 139.9°W 85 kt 100 mph
120 hour 08/09 0600Z 16.2°N 147.2°W 80 kt 90 mph

Track forecast



Figure 6. My forecast track for Julio.

2014 Atlantic hurricane season 2014 Pacific hurricane season Tropical Storm Bertha Hurricane Iselle Tropical Depression Ten-E Tropical Storm Julio

Updated: 10:10 AM GMT on August 04, 2014

Permalink

Tropical weather analysis - August 3, 2014

By: KoritheMan, 7:01 AM GMT on August 03, 2014

Notice: All forecasts presented here are based upon my own knowledge of atmospheric dynamics. They are created using my knowledge of the various computer models, satellite interpretation, and other tools and parameters. These forecasts, while striving to be accurate, are not intended to supersede predictions by the National Hurricane Center. Always follow NWS protocol and forecasts.

Bertha

Disorganized Bertha is now north of the Greater Antilles. As of the 0600Z NHC intermediate advisory, the following information was posted on Bertha:

Wind: 45 mph, with higher gusts
Location: 20.2°N 70.5°W
Movement: NW at 21 mph
Pressure: 1012 mb

Bertha is not a well-organized tropical cyclone this evening. Satellite, surface, and aircraft observations indicate that if a well-defined center exists, it is likely very small. The aircraft has been reporting some light westerly winds along the south side of the cyclone this evening, so perhaps Bertha hangs on as a tropical cyclone for now. Before the center moved out of range, the long-range San Juan radar suggested that the sharp trough axis/weak low-level circulation comprising Bertha was moving just off the northern coast of the Dominican Republic. Convection is still very disorganized in association with the cyclone, with the heaviest shower activity confined to an unorganized band east of the low-level center stretching over Hispaniola and adjacent waters. Upper-level outflow has recently become better-defined to the west, signifying a slight decrease in vertical shear, although it remains quite restricted in that direction.



Figure 1. Latest infrared satellite image of Tropical Storm Bertha. Image credit: NOAA's Satellite Services Division (SSD).

Assuming the shear does not increase again in association with another disturbance over the Bahamas not far to the west of Bertha, environmental conditions should generally be far more hospitable over the western Atlantic than they were in the Caribbean and deep tropics. Water vapor data suggests that, while the atmosphere is still somewhat dry in the western Atlantic, this area of the basin is under a uniform southerly flow between a mid- to upper-level trough over the eastern United States and a subtropical ridge near Bermuda; this is far healthier than a northerly flow. With water temperatures that are plenty warm, some intensification seems probable over the next couple of days. Beyond 72 hours, waters cool significantly and the models show a sharp increase in westerly shear in association with a progressive mid- to upper-level trough moving south from the northeastern United States and Atlantic Canada. This is expected to initiate weakening beyond that time, and eventually, extratropical transition. Most of the guidance still makes Bertha a hurricane for a brief time as it accelerates in the westerlies, and my forecast will continue to do the same. It is still possible that Bertha could get a little stronger than indicated below during the recurvature phase if the trough interaction aligns perfectly.

Bertha's motion has been difficult to determine this evening, largely because the cyclone is so disorganized, but UW-CIMSS synoptic steering data and tracking the entirety of the cloud mass yields a northwestward motion, indicating that Bertha has turned as predicted. Most of the guidance has shifted westward compared to 24 hours ago, with most models now failing to recurve Bertha until along or just west of 75W. My forecast track is similar to the current NHC prediction, but is a little to the left of that prediction in the early period, and then a little to the right during the latter portion of the forecast period, as some of the models suggest that post-tropical Bertha could turn eastward at that time. This is also ever so slightly to the left of the latest TVCN prediction.

Some of the outlying guidance -- namely the NAVGEM and UKMET -- show Bertha becoming absorbed by the disturbance over the Bahamas. Given current convective trends, and since Bertha still has the larger circulation, this solution seems physically unlikely for now. Indeed, the latest run of the Canadian model has also backed off on intensifying the secondary low into a tropical cyclone ahead of Bertha, lending more credence to the likelihood of Bertha remaining a separate entity.

Intensity forecast

Initial 08/03 0300Z 19.5°N 69.7°W 40 kt 45 mph
12 hour 08/03 1200Z 21.0°N 71.3°W 40 kt 45 mph
24 hour 08/04 0000Z 23.2°N 73.5°W 40 kt 45 mph
36 hour 08/04 1200Z 25.0°N 75.0°W 45 kt 50 mph
48 hour 08/05 0000Z 28.5°N 74.5°W 55 kt 65 mph
72 hour 08/06 0000Z 34.9°N 69.9°W 65 kt 75 mph
96 hour 08/07 0000Z 39.1°N 61.3°W 60 kt 70 mph
120 hour 08/08 0000Z 43.8°N 51.0°W 45 kt 50 mph: extratropical

Track forecast



Figure 2. My forecast track for Bertha. My forecast track was made prior to the release of the 6z intermediate advisory, so the initial position will differ somewhat compared to the coordinates contained within that update.

NHC storm information

000
WTNT33 KNHC 030550
TCPAT3

BULLETIN
TROPICAL STORM BERTHA INTERMEDIATE ADVISORY NUMBER 9A
NWS NATIONAL HURRICANE CENTER MIAMI FL AL032014
200 AM AST SUN AUG 03 2014

...BERTHA EXPECTED TO MOVE NEAR THE TURKS AND CAICOS AND
SOUTHEASTERN BAHAMAS LATER TODAY...


SUMMARY OF 200 AM AST...0600 UTC...INFORMATION
----------------------------------------------
LOCATION...20.2N 70.5W
ABOUT 30 MI...45 KM N OF PUERTO PLATA DOMINICAN REPUBLIC
ABOUT 95 MI...150 KM SE OF GRAND TURK ISLAND
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...NW OR 310 DEGREES AT 21 MPH...33 KM/H
MINIMUM CENTRAL PRESSURE...1012 MB...29.88 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY...

NONE.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* THE EASTERN DOMINICAN REPUBLIC FROM CABO FRANCES VIEJO TO
ISLA SAONA
* THE SOUTHEASTERN BAHAMAS...INCLUDING THE ACKLINS...CROOKED
ISLAND...LONG CAY...THE INAGUAS...MAYAGUANA...AND THE RAGGED ISLANDS
* THE TURKS AND CAICOS ISLANDS

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* CENTRAL BAHAMAS...INCLUDING CAT ISLAND...THE EXUMAS...LONG
ISLAND...RUM CAY...AND SAN SALVADOR

A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA...IN THIS CASE WITHIN
THE NEXT 12 TO 24 HOURS.

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...IN THIS CASE WITHIN 24 HOURS.

INTERESTS ELSEWHERE ACROSS HISPANIOLA AND THE BAHAMAS SHOULD MONITOR
THE PROGRESS OF THIS SYSTEM.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA OUTSIDE OF THE
UNITED STATES...PLEASE MONITOR PRODUCTS ISSUED BY YOUR NATIONAL
METEOROLOGICAL SERVICE.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 200 AM AST...0600 UTC...THE CENTER OF TROPICAL STORM BERTHA WAS
LOCATED NEAR LATITUDE 20.2 NORTH...LONGITUDE 70.5 WEST. BERTHA IS
MOVING TOWARD THE NORTHWEST NEAR 21 MPH...33 KM/H...AND THIS
GENERAL MOTION IS EXPECTED TO CONTINUE TODAY. A TURN TOWARD THE
NORTH-NORTHWEST AND THEN TOWARD THE NORTH IS EXPECTED BY TONIGHT
AND EARLY MONDAY. ON THE FORECAST TRACK...THE CENTER OF BERTHA WILL
CONTINUE TO MOVE AWAY FROM THE NORTHEASTERN COAST OF THE DOMINICAN
REPUBLIC THIS MORNING...MOVE NEAR OR OVER THE SOUTHEASTERN BAHAMAS
AND TURKS AND CAICOS ISLANDS BY THIS AFTERNOON...AND MOVE EAST OF
THE CENTRAL BAHAMAS LATE TONIGHT.

MAXIMUM SUSTAINED REMAIN NEAR 45 MPH...75 KM/H...WITH HIGHER GUSTS.
LITTLE CHANGE IN STRENGTH IS EXPECTED TODAY. SOME STRENGTHENING IS
POSSIBLE ON MONDAY AND TUESDAY.

TROPICAL-STORM-FORCE WINDS EXTEND OUTWARD UP TO 160 MILES...260
KM...MAINLY TO THE NORTHEAST OF THE CENTER.

THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 1012 MB...29.88 INCHES.


HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM CONDITIONS ARE EXPECTED IN PORTIONS OF THE
EASTERN DOMINICAN REPUBLIC IN THE WARNING AREA DURING THE NEXT FEW
HOURS. TROPICAL STORM CONDITIONS ARE EXPECTED IN THE SOUTHEASTERN
BAHAMAS AND THE TURKS AND CAICOS ISLANDS BY THIS AFTERNOON. TROPICAL
STORM CONDITIONS ARE POSSIBLE IN THE WATCH AREA IN THE CENTRAL
BAHAMAS BY THIS EVENING.

RAINFALL...BERTHA IS EXPECTED TO PRODUCE RAINFALL AMOUNTS OF 1 TO 3
INCHES WITH ISOLATED AMOUNTS UP TO 5 INCHES ACROSS PORTIONS OF THE
LEEWARD ISLANDS...EASTERN PORTIONS OF THE DOMINICAN REPUBLIC AS WELL
AS THE TURKS AND CAICOS THROUGH TONIGHT. ADDITIONAL RAINFALL
AMOUNTS OF UP TO 1 INCH ARE POSSIBLE ACROSS PUERTO RICO THROUGH
THIS MORNING.


NEXT ADVISORY
-------------
NEXT COMPLETE ADVISORY...500 AM AST.

$$
FORECASTER STEWART


Iselle

Iselle continues to move across the open Pacific. As of the 0300Z NHC advisory, the following coordinates were given on the storm:

Wind: 110 mph, with higher gusts
Location: 15.2°N 131.0°W
Movement: W at 10 mph
Pressure: 968 mb
Category: 2 (Saffir-Simpson Hurricane Wind Scale)

The satellite presentation of Iselle remains impressive. Although a ragged, cloud-filled eye has periodically been apparent in infrared satellite imagery, the eyewall convection has not quite been able to fully wrap around this feature, with some noticeable struggles on the south and western sides of the eye. Satellite estimates have not changed appreciably, and the 6z ATCF file from the NHC maintained Iselle as a 95 kt hurricane. Upper-tropospheric outflow remains well-defined except to the north, where some north-northeasterly shear continues to restrict upper ventilation in that area.



Figure 3. Latest infrared satellite image of Hurricane Iselle. Image credit: NOAA's Satellite Services Division (SSD).

Since Iselle is still under SSTs of around 27.5C, the main factor controlling additional intensification of Iselle over the next 12-24 hours will be inner core fluctuations. Although water vapor imagery suggests a bit of shear in the near-storm environment, there is not much evidence that this shear is penetrating the core at this time. On the flip side, there is a ton of dry air not far to the west of Iselle, which could still become entrained into the core even considering a lack of northwesterly shear to pull it into the core. The guidance does not suggest much, if any additional strengthening, but if the eye ever pops out and becomes more persistent, or if thunderstorms wrap more fully around the eye, Iselle could briefly become a major hurricane. Beyond 24 hours, waters cool to around 26C throughout the forecast period. Also, Iselle will be moving through a considerably drier airmass from then on, with the possibility of westerly shear remaining a viable one beyond about 72 hours, although the GFS and ECMWF are somewhat less enthusiastic about this prospect than they were yesterday. In fact, looking at the 850-200 mb averaged shear in those models, it appears that Iselle may even remain south of the strongest shear associated with a digging trough along 130W; if it does, it could be stronger than indicated below even during the weakening phase, as upper-level divergence is increased ahead of the trough. At any rate, Iselle is not likely to be a hurricane when it makes its closest approach to the Hawaiian Islands next week.

Iselle has been moving westward over the last 24 hours, as the subtropical ridge to the north of the hurricane has been stronger than originally predicted. This evening, there was little noticeable difference in the TVCE model consensus between 18 and 0z, and my forecast track is a close reflection of the current National Hurricane Center prediction. Iselle is forecast to continue moving generally west along the south side of the subtropical ridge until it gets west of 140W, after which most of the guidance suggests a turn toward the west-northwest as another mid- to upper-level trough digs southward along 150W. Most of the global models have shifted northward over the last 24 hours, with many now indicating a threat to the Big Island in about 5 or 6 days. The specifics of this threat are still highly uncertain and conditional upon the strength of the trough forecast to dig later in the period. Interests there should continue to monitor the progress of Iselle very carefully over the next few days.

Intensity forecast

Initial 08/03 0300Z 15.2°N 131.0°W 95 kt 110 mph
12 hour 08/03 1200Z 15.3°N 133.1°W 105 kt 120 mph
24 hour 08/04 0000Z 15.4°N 134.6°W 100 kt 115 mph
36 hour 08/05 0000Z 15.6°N 136.6°W 90 kt 105 mph
48 hour 08/05 1200Z 15.7°N 138.2°W 85 kt 100 mph
72 hour 08/06 0000Z 15.9°N 142.4°W 80 kt 90 mph
96 hour 08/07 0000Z 16.7°N 146.1°W 60 kt 70 mph
120 hour 08/08 0000Z 17.8°N 151.7°W 45 kt 50 mph

Track forecast



Figure 4. My forecast track for Iselle.

2014 Atlantic hurricane season 2014 Pacific hurricane season Tropical Storm Bertha Hurricane Iselle

Updated: 7:06 AM GMT on August 03, 2014

Permalink

Tropical weather analysis - August 1, 2014

By: KoritheMan, 4:34 AM GMT on August 02, 2014

Notice: All forecasts presented here are based upon my own knowledge of atmospheric dynamics. They are created using my knowledge of the various computer models, satellite interpretation, and other tools and parameters. These forecasts, while striving to be accurate, are not intended to supersede predictions by the National Hurricane Center. Always follow NWS protocol and forecasts.

Bertha

Tropical Storm Bertha continues across the eastern Caribbean Sea as a disorganized tropical storm. As of the 0300Z NHC advisory, the following information was posted on the system:

Wind: 50 mph, with higher gusts
Location: 15.7°N 63.0°W
Movement: WNW at 22 mph
Pressure: 1007 mb

Bertha is looking highly disorganized this evening, with latest shortwave infrared satellite data showing an exposed low-level center along the western end of the convection, which in itself has an elongated appearance. The hurricane hunters apparently had difficulty in closing off a center at 5000 feet according to the recent National Hurricane Center discussion, and surface observations from the Lesser Antilles indicates that the cyclone has a very broad circulation. A partial ASCAT pass captured areas of the Caribbean not far west of Bertha's estimated center at 0211Z and suggests that whatever circulation exists is probably very small. There is some prominent outflow to the east, but water vapor and satellite data suggest that some residual northwesterly shear remains, which is restricting outflow in the western quadrant.



Figure 1. Latest infrared satellite image of Tropical Storm Bertha. Image credit: NOAA's Satellite Services Division (SSD).

Although there is some evidence that the vertical shear over the eastern Caribbean may be decreasing (and indeed, the GFS, SHIPS, and ECMWF do signify a decrease in shear while Bertha moves across this area), there is still considerable dry air in the vicinity of the cyclone. Coupled with the highly disheveled satellite appearance, this suggests that little significant change in intensity is likely prior to the cyclone interacting with Puerto Rico and Hispaniola. Many of the global models initialize only a weak low, and the ECMWF continues to quickly dissipate the system. Subsequent to interacting with the islands and emerging north of the Greater Antilles, the GFS and ECMWF suggest that Bertha could find itself in a more favorable upper-level environment with lowering shear and increasing moisture, which would make sense with a slight westward building of the subtropical ridge. Most of the guidance now shows Bertha becoming a hurricane by days four and five, and my forecast will follow suit. It should be noted that tropical cyclones often reach their peak intensity at the point of recurvature, and Bertha could certainly get stronger than forecast here, especially when you factor in that acceleration in the westerlies will tend to enhance the winds in the eastern semicircle. In the short-term, an increasingly viable scenario is that Bertha degenerates into a sharp tropical wave while moving across the eastern Caribbean, a scenario which continues to be supported by the ECMWF and UKMET guidance, which have failed to intensify Bertha all along. If that did occur, regeneration would be possible in the western Atlantic.

It is a little difficult to tell which way Bertha is moving this evening since the center is small and diffuse. Recent imagery suggests a motion toward the west, but the longer-term motion has been generally west-northwest if we track the entire cloud envelope. The westward motion is assumed to be temporal due to the exposed circulation, and the guidance is still in good agreement on a west-northwestward motion, a scenario which continues to be supported by a residual mid- to upper-level trough over the United States east coast inducing a persistent weakness in the western extent of the subtropical ridge. Water vapor and UW-CIMSS synoptic steering data suggest that the ridge has built a little bit westward today, which could impart more of a leftward component of motion to the cyclone in the near-term, although my forecast is not explicitly deviating from the model consensus to account for that possibility until it becomes a likely one. Most of the models show Bertha passing near or over southwestern Puerto Rico Saturday afternoon. Once Bertha moves into the western Atlantic, the GFS and ECMWF continue to project a slight westward extension of the subtropical ridge as the current trough retrogrades westward and weakens. While this could impart a little bit of a westward motion over the cyclone as it moves through the Bahamas, a secondary trough -- this one of far less amplitude -- is forecast to drop southward out of New England and Atlantic Canada and reinforce the cyclonic flow over the western Atlantic, which the guidance agrees should recurve Bertha between the United States east coast and Bermuda. There are still some differences on the sharpness of recurvature, as well as how quickly Bertha will move during that period, with the ECMWF being farther left than the GFS. Since ridging has been rather persistent over Atlantic Canada and New England this year, my forecast will mimic the National Hurricane Center forecast track, except a couple of degrees to the west near the end of the period. This is also to the west of the model consensus TVCN, which recurves Bertha east of 75W.

Locally heavy rainfall and tropical storm force wind gusts will be possible over portions of the Lesser Antilles and Puerto Rico through the next 24 hours, particularly over higher elevations. The south side of Bertha currently appears rather weak, so unless things change, I don't foresee any significant flooding problems across the normally vulnerable landmass of Hispaniola.

Intensity forecast

Initial 08/02 0000Z 15.2°N 61.9°W 45 kt 50 mph
12 hour 08/02 1200Z 17.0°N 65.5°W 45 kt 50 mph
24 hour 08/03 0000Z 18.3°N 68.2°W 45 kt 50 mph
36 hour 08/03 1200Z 20.5°N 71.2°W 45 kt 50 mph
48 hour 08/04 0000Z 23.1°N 73.5°W 45 kt 50 mph
72 hour 08/05 0000Z 27.6°N 74.8°W 55 kt 65 mph
96 hour 08/06 0000Z 33.1°N 71.2°W 65 kt 75 mph
120 hour 08/07 0000Z 38.5°N 61.4°W 65 kt 75 mph

Track forecast



Figure 2. My forecast track for Bertha. My forecast track was compiled using the 0z position, so it's obviously going to differ somewhat from the 3z position estimate.

NHC storm information

000
WTNT33 KNHC 020245
TCPAT3

BULLETIN
TROPICAL STORM BERTHA ADVISORY NUMBER 5
NWS NATIONAL HURRICANE CENTER MIAMI FL AL032014
1100 PM AST FRI AUG 01 2014

...DISORGANIZED BERTHA MOVING WEST-NORTHWESTWARD ACROSS THE
NORTHEASTERN CARIBBEAN SEA...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...15.7N 63.0W
ABOUT 180 MI...295 KM SE OF ST. CROIX
ABOUT 275 MI...445 KM SE OF SAN JUAN PUERTO RICO
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...WNW OR 290 DEGREES AT 22 MPH...35 KM/H
MINIMUM CENTRAL PRESSURE...1007 MB...29.74 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY...

THE TROPICAL STORM WARNING FOR DOMINICA HAS BEEN DISCONTINUED.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* MARTINIQUE
* PUERTO RICO
* VIEQUES
* CULEBRA
* U.S. VIRGIN ISLANDS
* BRITISH VIRGIN ISLANDS

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* THE EASTERN DOMINICAN REPUBLIC FROM CABO FRANCES VIEJO TO
ISLA SAONA
* THE SOUTHEASTERN BAHAMAS...INCLUDING THE ACKLINS...CROOKED
ISLAND...LONG CAY...THE INAGUAS...MAYAGUANA...AND THE RAGGED ISLANDS
* THE TURKS AND CAICOS ISLANDS

A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA...IN THIS CASE WITHIN
THE NEXT 12 TO 24 HOURS.

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...IN THIS CASE WITHIN 24 TO 36
HOURS.

INTERESTS ELSEWHERE ACROSS THE NORTHEASTERN CARIBBEAN SEA AND
HISPANIOLA SHOULD MONITOR THE PROGRESS OF THIS SYSTEM.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA IN THE UNITED STATES...
INCLUDING POSSIBLE INLAND WATCHES AND WARNINGS...PLEASE MONITOR
PRODUCTS ISSUED BY YOUR LOCAL NATIONAL WEATHER SERVICE FORECAST
OFFICE. FOR STORM INFORMATION SPECIFIC TO YOUR AREA OUTSIDE THE
UNITED STATES...PLEASE MONITOR PRODUCTS ISSUED BY YOUR NATIONAL
METEOROLOGICAL SERVICE.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 1100 PM AST...0300 UTC...THE CENTER OF TROPICAL STORM BERTHA WAS
LOCATED NEAR LATITUDE 15.7 NORTH...LONGITUDE 63.0 WEST. BERTHA IS
MOVING TOWARD THE WEST-NORTHWEST NEAR 22 MPH...35 KM/H...AND THIS
MOTION IS EXPECTED TO CONTINUE TONIGHT AND SATURDAY. A TURN TOWARD
THE NORTHWEST IS EXPECTED BY SATURDAY NIGHT...AND THIS MOTION IS
EXPECTED TO CONTINUE THROUGH SUNDAY. ON THE FORECAST TRACK...THE
CENTER OF BERTHA WILL CONTINUE MOVING ACROSS THE NORTHEASTERN
CARIBBEAN SEA OVERNIGHT...PASS NEAR PUERTO RICO ON SATURDAY...MOVE
NEAR OR OVER THE EASTERN DOMINICAN REPUBLIC LATE SATURDAY AND
SATURDAY NIGHT...AND APPROACH THE SOUTHEASTERN BAHAMAS AND THE
TURKS AND CAICOS ISLANDS ON SUNDAY.

DATA FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INDICATE
THAT MAXIMUM SUSTAINED WINDS REMAIN NEAR 50 MPH...85 KM/H...WITH
HIGHER GUSTS. BERTHA REMAINS IN AN ENVIRONMENT THAT IS NOT FAVORABLE
FOR STRENGTHENING...AND LITTLE CHANGE IN STRENGTH IS FORECAST
THROUGH SUNDAY.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 115 MILES...185
KM...MAINLY TO THE NORTH AND EAST OF THE CENTER. GUADELOUPE
RECENTLY REPORTED A WIND GUST OF 37 MPH...59 KM/H.

THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 1007 MB...29.74 INCHES.


HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM FORCE WIND GUSTS ARE POSSIBLE OVER DOMINICA
AND GUADELOUPE DURING THE NEXT FEW HOURS. TROPICAL STORM CONDITIONS
ARE EXPECTED IN PUERTO RICO AND THE VIRGIN ISLANDS ON SATURDAY. WIND
GUSTS TO TROPICAL STORM FORCE COULD OCCUR IN SQUALLS OVER THE
REMAINDER OF THE LEEWARD ISLANDS. TROPICAL STORM CONDITIONS ARE
POSSIBLE IN THE WATCH AREA IN THE DOMINICAN REPUBLIC BY LATE
SATURDAY...AND IN THE SOUTHEASTERN BAHAMAS AND THE TURKS AND CAICOS
ISLANDS BY EARLY SUNDAY.

RAINFALL...BERTHA IS EXPECTED TO PRODUCE RAINFALL AMOUNTS OF 1 TO 3
INCHES WITH ISOLATED AMOUNTS UP TO 5 INCHES ACROSS PORTIONS OF THE
LEEWARD ISLANDS...AS WELL AS THE U.S. AND BRITISH VIRGIN ISLANDS.
RAINFALL TOTALS OF 3 TO 5 INCHES WITH ISOLATED MAXIMUM TOTALS OF 8
INCHES ARE POSSIBLE ACROSS PUERTO RICO...WITH THE HEAVIEST TOTALS
ACROSS THE SOUTHERN PORTION OF THE ISLAND.


NEXT ADVISORY
-------------
NEXT INTERMEDIATE ADVISORY...200 AM AST.
NEXT COMPLETE ADVISORY...500 AM AST.

$$
FORECASTER BRENNAN



Iselle

Iselle has become a hurricane, the fourth of the 2014 Pacific season. As of the latest NHC advisory, the following information was posted on the storm:

Wind: 75 mph, with higher gusts
Location: 14.7°N 127.3°W
Movement: WNW at 12 mph
Pressure: 992 mb

The satellite presentation of Iselle has continued to improve since the release of the 0300Z advisory. Cold convection -- between -65 and -70C -- is wrapping cyclonically into a ragged and cloud-filled eye; this feature is well-defined in evening microwave data, possibly portending a period of rapid intensification if the abundance of dry air just to the west of the storm fails to become entrained into the circulation. The SHIPS rapid intensification index is only indicating a 22% chance of a 25-kt increase in wind speed during the next 24 hours, likely in response to the marginal thermodynamics. Upper-tropospheric outflow is well-defined except to the north, where it remains restricted due to light northerly shear.



Figure 3. Latest infrared satellite image of Hurricane Iselle. Image credit: NOAA's Satellite Services Division (SSD).

Since expanding circulations often have a problem with dry air entrainment from nearby dry airmasses, my forecast will be a little more conservative and more in line with the SHIPS guidance, which brings the hurricane up to 75 kt in about 24 hours. If Iselle fails to swallow the dry air, rapid intensification to major hurricane strength remains a distinct possibility. In about 36 hours, the SHIPS model shows SSTs decreasing to below 27C, which would likely put an end to any additional intensification, particularly if that intensification is rapid. Additionally, the hurricane will be entering an increasingly drier airmass by that time, and the GFS and ECMWF show westerly shear increasingly sharply between 96-120 hours, although with differing magnitudes, presumably due to the GFS having a track that is a bit farther north than the ECMWF. Lastly, water temperatures and oceanic heat content will decrease even more as Iselle moves farther west, with water temperatures likely falling to below 26C by days four and five. A weakening trend is anticipated beyond 36 hours, with that weakening becoming hastened near the end of the forecast period. It is possible that Iselle could weaken faster than I've shown below if the shear increases as much as it theoretically could.

Iselle has been moving generally west-northwest along the south side of the subtropical ridge. The most recent data suggests that the motion could be deviating a little bit to the south of the latest NHC track prediction. Water vapor imagery shows that the models may be underestimating the strength of the ridge; the upper low and associated mid- to upper-level trough near 43N 146W is retreating northward for now. While this was well advertised by the global models yesterday, based on the current motion and water vapor data, my guess is these models may have underestimated the swiftness of the retreat, as well as the strength of the high. Having said all of that, the models continue to be in excellent agreement on Iselle moving west-northwestward during the next day or two. After that, they indicate a turn to the west, but with considerable differences in the sharpness and timing of that westward turn. The GFS continues to be farther north than the ECMWF, although compared to yesterday, that model is a good bit farther south, closer to the more westward ECMWF, which has always been a persistent solution. In general, the guidance shows a stronger subtropical ridge today, but I am not convinced that tells the whole story in terms of the anticipated westward motion. Satellite data suggests that the circulation associated with disturbance 97E several hundred miles to the east of Iselle is quickly developing a rather large and atypical circulation, which is line with what most of the guidance has been forecasting for days. Most of the models, with the exception of the GFDL and HWRF, suggest that this disturbance will compete with Iselle's circulation, causing slow and erratic motion as the cyclone nears the central Pacific in a few days. While I don't expect the circulation associated with this system to shrink or unwind over the next few days, the depth of organization and development remains in question until we get a tropical cyclone... if we do. Because of this... and since the models could easily flip back, my forecast track will remain similar to the one I made yesterday. This is also close to the latest National Hurricane Center prediction. If the seeming westward initial motion persists, Iselle will undoubtedly track farther south of this prediction.

While some of the long-range guidance -- including the GFS and ECMWF -- take Iselle not far south of the Big Island next week, it is too early to ascertain the specifics of this threat. Interests in Hawaii should monitor the progress of this system over the next few days.

Intensity forecast

Initial 08/02 0300Z 14.7°N 127.3°W 65 kt 75 mph
12 hour 08/02 1200Z 15.2°N 128.8°W 70 kt 80 mph
24 hour 08/03 0000Z 15.3°N 130.3°W 75 kt 85 mph
36 hour 08/03 1200Z 15.7°N 131.7°W 75 kt 85 mph
48 hour 08/04 0000Z 16.1°N 133.4°W 70 kt 80 mph
72 hour 08/05 0000Z 16.4°N 135.7°W 60 kt 70 mph
96 hour 08/06 0000Z 16.8°N 139.8°W 50 kt 60 mph
120 hour 08/07 0000Z 17.5°N 145.1°W 40 kt 45 mph

Track forecast



Figure 4. My forecast track for Iselle.

2014 Atlantic hurricane season 2014 Pacific hurricane season Tropical Storm Bertha Tropical Storm Iselle Hurricane Iselle

Updated: 5:21 AM GMT on August 02, 2014

Permalink

Tropical weather analysis - August 1, 2014

By: KoritheMan, 8:20 AM GMT on August 01, 2014

Notice: All forecasts presented here are based upon my own knowledge of atmospheric dynamics. They are created using my knowledge of the various computer models, satellite interpretation, and other tools and parameters. These forecasts, while striving to be accurate, are not intended to supersede predictions by the National Hurricane Center. Always follow NWS protocol and forecasts.

Bertha

The persistent tropical wave that has been tracked over the Atlantic for several days finally became a tropical storm Thursday evening. As of the 0300Z NHC advisory (new one due out in about an hour), the following information was available on Bertha:

Wind: 45 mph, with higher gusts
Location: 12.6°N 56.3°W
Movement: WNW at 18 mph
Pressure: 1008 mb

Bertha continues to have a ragged appearance in satellite imagery. Although there is more persistent convection than over the last few days, at times suggestive of primitive banding, water vapor data indicates that the cyclone remains embedded in an atmospheric environment that is marginal at best, both at the thermal and shear spectrum. As a result of the dry air and westerly shear associated with that environment, it is not surprising that the low-level center is exposed along the western edge of the convection, a situation which was apparent in both conventional satellite and microwave satellite data as well. In fact, the latest satellite estimates suggests that 40 kt could be a generous intensity estimate.



Figure 1. Latest infrared satellite image of Tropical Storm Bertha. Image credit: NOAA's Satellite Services Division (SSD).

The environment is not likely to become particularly favorable ahead of Bertha for at least the next 72 hours. Water vapor imagery continues to show high cirrus blowing eastward toward the cyclone in association with a well-defined upper cold low embedded within the mid-oceanic trough. While the GFS and ECMWF retrograde and weaken this low over the next few days, there is still a lot of dry air ahead of the tropical storm, with 0z upper air data showing a layer of very dry air aloft at 700 mb on the island of Saint Martin, located along the northern portion of the Lesser Antilles island chain. In addition, the majority of the model guidance this morning shows Bertha making landfall in eastern Hispaniola in about 36 hours, which is likely to disrupt the low-level circulation. One positive is that Bertha's horizontal circulation envelope remains rather large, which will mean much of the outer circulation will still be over water even as Bertha moves inland; this could limit the amount of weakening typically associated with the rugged terrain of Hispaniola. After about 72 hours, the GFS and ECMWF show the upper-tropospheric shear could lessen somewhat as Bertha enters the western Atlantic, although it is uncertain how much northwesterly shear on the backside of a retreating upper-level trough may affect the cyclone at that time. I'll show a little bit of strengthening at days four and five in response to this environment, but at this stage, Bertha appears unlikely to become a hurricane. Many of the global models do not intensify Bertha, and the ECMWF continues to dissipate the system.

Bertha continues to move toward the west-northwest on the south side of a strong subtropical ridge. Water vapor imagery suggests a residual weakness remains within the western portion of this ridge in association with a persistent mid- to upper-level trough along the eastern United States. The models gradually weaken this trough over the next few days and show it retreating westward, which should allow some mid-tropospheric ridging to develop to the north of Bertha as it enters the western Atlantic. While this would ordinarily portend a continuation into the coast, the models are in good agreement that a progressive shortwave trough will dive southward out of Atlantic Canada in the day 4/5 period, which should be sufficient to recurve Bertha into the westerlies between the United States east coast and Bermuda. The guidance remains in good agreement on the forecast track. My forecast track is similar to the TVCN model consensus, but is a bit to the west of that guidance at the end of the period.

While unlikely, there is a nonzero chance of a landfall along the United States mid-Atlantic coast mostly due to the progressive nature of the aforementioned shortwave. The most likely scenario is recurvature, but interests in that area should continue to carefully monitor the progress of this tropical storm over the next several days.

In the meantime, heavy rainfall and tropical storm force winds in squalls will begin affecting the Lesser Antilles in about 18-24 hours before spreading into Puerto Rico and Hispaniola. Watches and warnings have been issued for portions of these areas (see below).

Intensity forecast

Initial 08/01 0600Z 12.6°N 56.3°W 40 kt 45 mph
12 hour 08/01 1800Z 13.3°N 59.3°W 40 kt 45 mph
24 hour 08/02 0600Z 14.3°N 62.2°W 40 kt 45 mph
36 hour 08/02 1800Z 15.5°N 64.5°W 40 kt 45 mph
48 hour 08/03 0600Z 17.8°N 67.9°W 40 kt 45 mph
72 hour 08/04 0600Z 22.1°N 72.1°W 40 kt 45 mph
96 hour 08/05 0600Z 26.1°N 75.2°W 45 kt 50 mph
120 hour 08/06 0600Z 31.6°N 74.8°W 50 kt 60 mph

Track forecast



Figure 2. My forecast track for Bertha.

NHC storm information

000
WTNT33 KNHC 010542
TCPAT3

BULLETIN
TROPICAL STORM BERTHA INTERMEDIATE ADVISORY NUMBER 1A
NWS NATIONAL HURRICANE CENTER MIAMI FL AL032014
200 AM AST FRI AUG 01 2014

...TROPICAL STORM BERTHA HEADING TOWARD THE LESSER ANTILLES...


SUMMARY OF 200 AM AST...0600 UTC...INFORMATION
----------------------------------------------
LOCATION...12.6N 56.3W
ABOUT 215 MI...345 KM E OF BARBADOS
ABOUT 320 MI...520 KM ESE OF ST. LUCIA
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...WNW OR 290 DEGREES AT 18 MPH...30 KM/H
MINIMUM CENTRAL PRESSURE...1008 MB...29.77 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY...

THE GOVERNMENT OF THE BRITISH VIRGIN ISLANDS HAS ISSUED A TROPICAL
STORM WATCH FOR THE BRITISH VIRGIN ISLANDS.

A TROPICAL STORM WARNING COULD BE REQUIRED FOR MARTINIQUE LATER
TODAY.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* BARBADOS
* ST. LUCIA
* DOMINICA

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* PUERTO RICO
* VIEQUES
* CULEBRA
* U.S. VIRGIN ISLANDS
* BRITISH VIRGIN ISLANDS
* ST. VINCENT AND THE GRENADINES

A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA...IN THIS CASE WITHIN
THE NEXT 24 HOURS.

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 48 HOURS.

INTERESTS ELSEWHERE ACROSS THE NORTHEASTERN CARIBBEAN SEA SHOULD
MONITOR THE PROGRESS OF THIS SYSTEM.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA IN THE UNITED
STATES...INCLUDING POSSIBLE INLAND WATCHES AND WARNINGS...PLEASE
MONITOR PRODUCTS ISSUED BY YOUR LOCAL NATIONAL WEATHER SERVICE
FORECAST OFFICE. FOR STORM INFORMATION SPECIFIC TO YOUR AREA OUTSIDE
THE UNITED STATES...PLEASE MONITOR PRODUCTS ISSUED BY YOUR NATIONAL
METEOROLOGICAL SERVICE.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 200 AM AST...0600 UTC...THE CENTER OF TROPICAL STORM BERTHA WAS
LOCATED NEAR LATITUDE 12.6 NORTH...LONGITUDE 56.3 WEST. BERTHA IS
MOVING TOWARD THE WEST-NORTHWEST NEAR 18 MPH...30 KM/H...AND THIS
GENERAL MOTION IS EXPECTED TO CONTINUE FOR THE NEXT COUPLE OF DAYS.
ON THE FORECAST TRACK...BERTHA IS EXPECTED TO PASS NEAR BARBADOS
THIS AFTERNOON AND MOVE THROUGH THE CENTRAL LESSER ANTILLES FRIDAY
EVENING.

MAXIMUM SUSTAINED WINDS REMAIN NEAR 45 MPH...75 KM/H...WITH
HIGHER GUSTS. LITTLE CHANGE IN STRENGTH IS FORECAST DURING THE NEXT
48 HOURS.

TROPICAL-STORM-FORCE WINDS EXTEND OUTWARD UP TO 45 MILES...75 KM
FROM THE CENTER.

THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 1008 MB...29.77 INCHES.


HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM CONDITIONS ARE EXPECTED TO FIRST REACH THE
WARNING AREA BY MIDDAY TODAY...MAKING OUTSIDE PREPARATIONS
DIFFICULT OR DANGEROUS. TROPICAL STORM CONDITIONS ARE POSSIBLE IN
THE WATCH AREA IN PUERTO RICO AND THE VIRGIN ISLANDS ON SATURDAY.

RAINFALL...BERTHA IS EXPECTED TO PRODUCE RAINFALL AMOUNTS OF 1 TO
3 INCHES WITH ISOLATED AMOUNTS UP TO 5 INCHES ACROSS PORTIONS OF THE
LEEWARD ISLANDS...PUERTO RICO...AND THE VIRGIN ISLANDS THROUGH
SATURDAY NIGHT.


NEXT ADVISORY
-------------
NEXT COMPLETE ADVISORY...500 AM AST.

$$
FORECASTER AVILA



Iselle

Tropical Storm Iselle is moving across the open Pacific well away from land. As of the 0300Z NHC advisory bulletin, the following information was posted on Iselle:

Wind: 45 mph, with higher gusts
Location: 13.2°N 123.9°W
Movement: WNW at 12 mph
Pressure: 1005 mb

Iselle is exhibiting a very impressive cloud signature on satellite imagery this morning. The cyclone is generating very deep convection (up to and perhaps a bit above -80C) amidst what appears to be the initial stages of a central dense overcast. Microwave data suggests that the low-level center is located just to the west of the heaviest thunderstorms, with some indication of those storms attempting to consolidate around the center, with the imagery suggestive that there could be a formative eyewall. Satellite estimates have risen considerably, with the most recent final T number from the CIMSS ADT at 3.5/55 kt. The 6z NHC ATCF file assigned Iselle with an intensity of 50 kt at synoptic time; perhaps that will be increased to 55 kt in the forthcoming advisory, or maybe not. Upper-level outflow remains well-defined except to the west, where it appears to be experiencing restriction.



Figure 3. Latest infrared satellite image of Tropical Storm Iselle. Image credit: NOAA's Satellite Services Division (SSD).

The environment is conducive for additional strengthening, with the models showing an environment that may not exactly be anticyclonic, but is at least diffluent and of light shear. In addition, Iselle appears to be embedded within a very moist environment. Most of the explicit intensity guidance has trended upward this cycle, and even the global models generally suggest some intensification. My forecast is similar to the SHIPS model, which appears to be handling Iselle rather nicely at the moment; this will take the cyclone up to 80 kt in 48 hours. While the SHIPS rapid intensification index is a little less this cycle, this could just be a flop in the model, and it remains a viable possibility that Iselle could strengthen quicker than indicated here, possibly becoming a major hurricane if current trends persist. In about 72 hours, sea surface temperatures cool ahead of the storm, and water vapor imagery suggests some dry mid-level air between 130 and 135W. The GFS actually shows an increase in shear during the latter portion of the forecast period as well, but the ECMWF shows less shear, presumably because its respective track for Iselle is considerably farther south. A weakening trend is anticipated beyond day three, with Iselle dropping below hurricane strength by day five.

Iselle continues moving toward the west-northwest, pretty much in line with the NHC track prediction. The models are unanimous on having Iselle maintain this general motion over the next 48-72 hours. After that time, there is considerable divergence in the guidance. The GFS and NAVGEM show a track toward Hawaii beyond day five, while the ECMWF and UKMET show Iselle moving westward to the south of the archipelago. Since the ECMWF appears to move Iselle a little slower than the GFS, possibly in response to a modeled interaction with another disturbance to the east, and since Iselle is likely to be a somewhat deeper system than the ECMWF is indicating, I have based my own forecast track off a careful blend of the two models, not fully committing to the northward turn shown on the GFS, but also not quite ready to accept the hard westward turn projected by the ECMWF.

Interests in Hawaii should monitor the progress of Iselle through the middle of next week.

Intensity forecast

Initial 08/01 0600Z 13.4°N 124.2°W 50 kt 60 mph
12 hour 08/02 1800Z 14.0°N 126.0°W 55 kt 65 mph
24 hour 08/03 0600Z 14.7°N 128.1°W 65 kt 75 mph
36 hour 08/03 1800Z 15.3°N 130.0°W 70 kt 80 mph
48 hour 08/04 0600Z 15.9°N 132.3°W 80 kt 90 mph
72 hour 08/04 0600Z 16.5°N 135.1°W 80 kt 90 mph
96 hour 08/05 0600Z 17.1°N 137.7°W 65 kt 75 mph
120 hour 08/06 0600Z 17.7°N 142.7°W 50 kt 60 mph

Track forecast



Figure 4. My forecast track for Iselle.

2014 Atlantic hurricane season 2014 Pacific hurricane season Tropical Storm Bertha Tropical Storm Iselle

Permalink

Tropical weather analysis - August 1, 2014

By: KoritheMan, 8:19 AM GMT on August 01, 2014

Notice: All forecasts presented here are based upon my own knowledge of atmospheric dynamics. They are created using my knowledge of the various computer models, satellite interpretation, and other tools and parameters. These forecasts, while striving to be accurate, are not intended to supersede predictions by the National Hurricane Center. Always follow NWS protocol and forecasts.

Bertha

The persistent tropical wave that has been tracked over the Atlantic for several days finally became a tropical storm Thursday evening. As of the 0300Z NHC advisory (new one due out in about an hour), the following information was available on Bertha:

Wind: 45 mph, with higher gusts
Location: 12.6°N 56.3°W
Movement: WNW at 18 mph
Pressure: 1008 mb

Bertha continues to have a ragged appearance in satellite imagery. Although there is more persistent convection than over the last few days, at times suggestive of primitive banding, water vapor data indicates that the cyclone remains embedded in an atmospheric environment that is marginal at best, both at the thermal and shear spectrum. As a result of the dry air and westerly shear associated with that environment, it is not surprising that the low-level center is exposed along the western edge of the convection, a situation which was apparent in both conventional satellite and microwave satellite data as well. In fact, the latest satellite estimates suggests that 40 kt could be a generous intensity estimate.



Figure 1. Latest infrared satellite image of Tropical Storm Bertha. Image credit: NOAA's Satellite Services Division (SSD).

The environment is not likely to become particularly favorable ahead of Bertha for at least the next 72 hours. Water vapor imagery continues to show high cirrus blowing eastward toward the cyclone in association with a well-defined upper cold low embedded within the mid-oceanic trough. While the GFS and ECMWF retrograde and weaken this low over the next few days, there is still a lot of dry air ahead of the tropical storm, with 0z upper air data showing a layer of very dry air aloft at 700 mb on the island of Saint Martin, located along the northern portion of the Lesser Antilles island chain. In addition, the majority of the model guidance this morning shows Bertha making landfall in eastern Hispaniola in about 36 hours, which is likely to disrupt the low-level circulation. One positive is that Bertha's horizontal circulation envelope remains rather large, which will mean much of the outer circulation will still be over water even as Bertha moves inland; this could limit the amount of weakening typically associated with the rugged terrain of Hispaniola. After about 72 hours, the GFS and ECMWF show the upper-tropospheric shear could lessen somewhat as Bertha enters the western Atlantic, although it is uncertain how much northwesterly shear on the backside of a retreating upper-level trough may affect the cyclone at that time. I'll show a little bit of strengthening at days four and five in response to this environment, but at this stage, Bertha appears unlikely to become a hurricane. Many of the global models do not intensify Bertha, and the ECMWF continues to dissipate the system.

Bertha continues to move toward the west-northwest on the south side of a strong subtropical ridge. Water vapor imagery suggests a residual weakness remains within the western portion of this ridge in association with a persistent mid- to upper-level trough along the eastern United States. The models gradually weaken this trough over the next few days and show it retreating westward, which should allow some mid-tropospheric ridging to develop to the north of Bertha as it enters the western Atlantic. While this would ordinarily portend a continuation into the coast, the models are in good agreement that a progressive shortwave trough will dive southward out of Atlantic Canada in the day 4/5 period, which should be sufficient to recurve Bertha into the westerlies between the United States east coast and Bermuda. The guidance remains in good agreement on the forecast track. My forecast track is similar to the TVCN model consensus, but is a bit to the west of that guidance at the end of the period.

While unlikely, there is a nonzero chance of a landfall along the United States mid-Atlantic coast mostly due to the progressive nature of the aforementioned shortwave. The most likely scenario is recurvature, but interests in that area should continue to carefully monitor the progress of this tropical storm over the next several days.

In the meantime, heavy rainfall and tropical storm force winds in squalls will begin affecting the Lesser Antilles in about 18-24 hours before spreading into Puerto Rico and Hispaniola. Watches and warnings have been issued for portions of these areas (see below).

Intensity forecast

Initial 08/01 0600Z 12.6°N 56.3°W 40 kt 45 mph
12 hour 08/01 1800Z 13.3°N 59.3°W 40 kt 45 mph
24 hour 08/02 0600Z 14.3°N 62.2°W 40 kt 45 mph
36 hour 08/02 1800Z 15.5°N 64.5°W 40 kt 45 mph
48 hour 08/03 0600Z 17.8°N 67.9°W 40 kt 45 mph
72 hour 08/04 0600Z 22.1°N 72.1°W 40 kt 45 mph
96 hour 08/05 0600Z 26.1°N 75.2°W 45 kt 50 mph
120 hour 08/06 0600Z 31.6°N 74.8°W 50 kt 60 mph

Track forecast



Figure 2. My forecast track for Bertha.

NHC storm information

000
WTNT33 KNHC 010542
TCPAT3

BULLETIN
TROPICAL STORM BERTHA INTERMEDIATE ADVISORY NUMBER 1A
NWS NATIONAL HURRICANE CENTER MIAMI FL AL032014
200 AM AST FRI AUG 01 2014

...TROPICAL STORM BERTHA HEADING TOWARD THE LESSER ANTILLES...


SUMMARY OF 200 AM AST...0600 UTC...INFORMATION
----------------------------------------------
LOCATION...12.6N 56.3W
ABOUT 215 MI...345 KM E OF BARBADOS
ABOUT 320 MI...520 KM ESE OF ST. LUCIA
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...WNW OR 290 DEGREES AT 18 MPH...30 KM/H
MINIMUM CENTRAL PRESSURE...1008 MB...29.77 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY...

THE GOVERNMENT OF THE BRITISH VIRGIN ISLANDS HAS ISSUED A TROPICAL
STORM WATCH FOR THE BRITISH VIRGIN ISLANDS.

A TROPICAL STORM WARNING COULD BE REQUIRED FOR MARTINIQUE LATER
TODAY.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* BARBADOS
* ST. LUCIA
* DOMINICA

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* PUERTO RICO
* VIEQUES
* CULEBRA
* U.S. VIRGIN ISLANDS
* BRITISH VIRGIN ISLANDS
* ST. VINCENT AND THE GRENADINES

A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA...IN THIS CASE WITHIN
THE NEXT 24 HOURS.

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 48 HOURS.

INTERESTS ELSEWHERE ACROSS THE NORTHEASTERN CARIBBEAN SEA SHOULD
MONITOR THE PROGRESS OF THIS SYSTEM.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA IN THE UNITED
STATES...INCLUDING POSSIBLE INLAND WATCHES AND WARNINGS...PLEASE
MONITOR PRODUCTS ISSUED BY YOUR LOCAL NATIONAL WEATHER SERVICE
FORECAST OFFICE. FOR STORM INFORMATION SPECIFIC TO YOUR AREA OUTSIDE
THE UNITED STATES...PLEASE MONITOR PRODUCTS ISSUED BY YOUR NATIONAL
METEOROLOGICAL SERVICE.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 200 AM AST...0600 UTC...THE CENTER OF TROPICAL STORM BERTHA WAS
LOCATED NEAR LATITUDE 12.6 NORTH...LONGITUDE 56.3 WEST. BERTHA IS
MOVING TOWARD THE WEST-NORTHWEST NEAR 18 MPH...30 KM/H...AND THIS
GENERAL MOTION IS EXPECTED TO CONTINUE FOR THE NEXT COUPLE OF DAYS.
ON THE FORECAST TRACK...BERTHA IS EXPECTED TO PASS NEAR BARBADOS
THIS AFTERNOON AND MOVE THROUGH THE CENTRAL LESSER ANTILLES FRIDAY
EVENING.

MAXIMUM SUSTAINED WINDS REMAIN NEAR 45 MPH...75 KM/H...WITH
HIGHER GUSTS. LITTLE CHANGE IN STRENGTH IS FORECAST DURING THE NEXT
48 HOURS.

TROPICAL-STORM-FORCE WINDS EXTEND OUTWARD UP TO 45 MILES...75 KM
FROM THE CENTER.

THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 1008 MB...29.77 INCHES.


HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM CONDITIONS ARE EXPECTED TO FIRST REACH THE
WARNING AREA BY MIDDAY TODAY...MAKING OUTSIDE PREPARATIONS
DIFFICULT OR DANGEROUS. TROPICAL STORM CONDITIONS ARE POSSIBLE IN
THE WATCH AREA IN PUERTO RICO AND THE VIRGIN ISLANDS ON SATURDAY.

RAINFALL...BERTHA IS EXPECTED TO PRODUCE RAINFALL AMOUNTS OF 1 TO
3 INCHES WITH ISOLATED AMOUNTS UP TO 5 INCHES ACROSS PORTIONS OF THE
LEEWARD ISLANDS...PUERTO RICO...AND THE VIRGIN ISLANDS THROUGH
SATURDAY NIGHT.


NEXT ADVISORY
-------------
NEXT COMPLETE ADVISORY...500 AM AST.

$$
FORECASTER AVILA



Iselle

Tropical Storm Iselle is moving across the open Pacific well away from land. As of the 0300Z NHC advisory bulletin, the following information was posted on Iselle:

Wind: 45 mph, with higher gusts
Location: 13.2°N 123.9°W
Movement: WNW at 12 mph
Pressure: 1005 mb

Iselle is exhibiting a very impressive cloud signature on satellite imagery this morning. The cyclone is generating very deep convection (up to and perhaps a bit above -80C) amidst what appears to be the initial stages of a central dense overcast. Microwave data suggests that the low-level center is located just to the west of the heaviest thunderstorms, with some indication of those storms attempting to consolidate around the center, with the imagery suggestive that there could be a formative eyewall. Satellite estimates have risen considerably, with the most recent final T number from the CIMSS ADT at 3.5/55 kt. The 6z NHC ATCF file assigned Iselle with an intensity of 50 kt at synoptic time; perhaps that will be increased to 55 kt in the forthcoming advisory, or maybe not. Upper-level outflow remains well-defined except to the west, where it appears to be experiencing restriction.



Figure 3. Latest infrared satellite image of Tropical Storm Iselle. Image credit: NOAA's Satellite Services Division (SSD).

The environment is conducive for additional strengthening, with the models showing an environment that may not exactly be anticyclonic, but is at least diffluent and of light shear. In addition, Iselle appears to be embedded within a very moist environment. Most of the explicit intensity guidance has trended upward this cycle, and even the global models generally suggest some intensification. My forecast is similar to the SHIPS model, which appears to be handling Iselle rather nicely at the moment; this will take the cyclone up to 80 kt in 48 hours. While the SHIPS rapid intensification index is a little less this cycle, this could just be a flop in the model, and it remains a viable possibility that Iselle could strengthen quicker than indicated here, possibly becoming a major hurricane if current trends persist. In about 72 hours, sea surface temperatures cool ahead of the storm, and water vapor imagery suggests some dry mid-level air between 130 and 135W. The GFS actually shows an increase in shear during the latter portion of the forecast period as well, but the ECMWF shows less shear, presumably because its respective track for Iselle is considerably farther south. A weakening trend is anticipated beyond day three, with Iselle dropping below hurricane strength by day five.

Iselle continues moving toward the west-northwest, pretty much in line with the NHC track prediction. The models are unanimous on having Iselle maintain this general motion over the next 48-72 hours. After that time, there is considerable divergence in the guidance. The GFS and NAVGEM show a track toward Hawaii beyond day five, while the ECMWF and UKMET show Iselle moving westward to the south of the archipelago. Since the ECMWF appears to move Iselle a little slower than the GFS, possibly in response to a modeled interaction with another disturbance to the east, and since Iselle is likely to be a somewhat deeper system than the ECMWF is indicating, I have based my own forecast track off a careful blend of the two models, not fully committing to the northward turn shown on the GFS, but also not quite ready to accept the hard westward turn projected by the ECMWF. This forecast is a little to the north of the National Hurricane Center prediction at days four and five.

Interests in Hawaii should monitor the progress of Iselle into the middle of next week.

Intensity forecast

Initial 08/01 0600Z 13.4°N 124.2°W 50 kt 60 mph
12 hour 08/02 1800Z 14.0°N 126.0°W 55 kt 65 mph
24 hour 08/03 0600Z 14.7°N 128.1°W 65 kt 75 mph
36 hour 08/03 1800Z 15.3°N 130.0°W 70 kt 80 mph
48 hour 08/04 0600Z 15.9°N 132.3°W 80 kt 90 mph
72 hour 08/04 0600Z 16.5°N 135.1°W 80 kt 90 mph
96 hour 08/05 0600Z 17.1°N 137.7°W 65 kt 75 mph
120 hour 08/06 0600Z 17.7°N 142.7°W 50 kt 60 mph

Track forecast



Figure 4. My forecast track for Iselle.

Tropical Storm Bertha Tropical Storm Iselle Tropical Depression Genevieve 2014 Atlantic hurricane season 2014 Pacific hurricane season

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About KoritheMan

I'm just a 23 year old with an ardent passion for weather. I first became aware of this interest after Tropical Storm Isidore struck my area in 2002.

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