KoritheMan's WunderBlog

Tropical weather analysis - July 31, 2013

By: KoritheMan, 3:19 AM GMT on August 01, 2013

Gil

Gil continues to strengthen as of the latest NHC advisory:

Wind: 80 mph, with higher gusts
Location: 14.2°N 121.8°W
Movement: WNW at 12 mph
Pressure: 990 mb
Category: 1 (Saffir-Simpson Hurricane Wind Scale)

Microwave fixes throughout the day have shown a small eye enveloped -- albeit not completely -- by a ring of deep convection. Earlier during the day, conventional satellite images showed that the eye seen in microwave data attempted to come out in the open around 1900 UTC, but this feature was short-lived, and since has been obscured by convection. As of this writing, a rather healthy burst of central convection is attempting to wrap cyclonically around where extrapolation would place the earlier observed eye, and now wraps about 75% around this feature. Upper tropospheric outflow remains well-defined.



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

Gil is located over SSTs of nearly 29C, and is forecast to remain under waters of at least 27C for the next 48 hours. Given that, the seemingly low shear, and the moist mid-level environment, the cyclone appears poised to continue strengthening, and there is still the potential for rapid intensification since Gil now appears to have an inner core. The intensity guidance has come up on this cycle, and most show Gil at or above the threshold of Category 2 intensity within the next 24 hours. I expect continued strengthening, and show Gil reaching 85 kt in 36 hours. However, the rate of intensification could be much quicker, especially if current trends persist. I would give Gil about a 30% chance of becoming a major hurricane during the next 24-36 hours. By 48 hours, waters are forecast to cool to the upper end of 26C, which is a lot when we're considering removing heat from a complex system like a tropical cyclone. Based on the cooler SST profiles, increasing westerly shear by that time, and the possibility of dry air entrainment near and west of 125W, I expect the hurricane to begin to wind down by that point, with a rather quick rate of weakening shown near the end of the period. It should be noted that the GFS and ECMWF have come southward relative to 24 hours ago, and should that verify, Gil will be over at least marginally warm waters throughout the period, and thus may be able to generate intermittent convection even after it loses its status a tropical cyclone.

Gil is south of a mid-level ridge. Water vapor imagery and CIMSS steering data reveal a rather large weakness to the north of this ridge from 120 to 130W, associated with a weak upper low and trailing upper trough spinning off the southwest coast of Baja California; this weakness appears to be getting reinforced by another upper low near 31.5N 144.0W. The global models suggest that Gil will continue moving generally west-northwest amidst this weakness for the next couple of days. After that time, when the system nears 130W, hostile environmental conditions are forecast to cause Gil to weaken; in combination with increasing distance from the Baja California upper low, the hurricane is forecast to turn more toward the west at that time. The second upper vortex, the one near 145W, is forecast by the models to hang around in the mid to upper troposphere, to the northeast of the Hawaiian Islands. While this may be enough to temporarily tug Gil a little more northward than is currently forecast, it should still sufficiently weaken to pass well south of the Hawaiian Islands, but high surf will likely impact windward facing beaches early next week regardless.

Intensity forecast and positions

INITIAL 08/01 0300Z 14.1°N 121.5°W 70 KT 80 MPH
12 hour 08/01 1200Z 14.6°N 123.8°W 75 KT 85 MPH
24 hour 08/02 0000Z 15.1°N 125.7°W 80 KT 90 MPH
36 hour 08/02 1200Z 15.3°N 127.1°W 85 KT 100 MPH
48 hour 08/03 0000Z 15.6°N 128.3°W 80 KT 90 MPH
72 hour 08/04 0000Z 16.1°N 130.9°W 65 KT 75 MPH
96 hour 08/05 0000Z 16.3°N 134.4°W 45 KT 50 MPH
120 hour 08/06 0000Z 16.3°N 138.2°W 30 KT 35 MPH

Track forecast



Figure 2. My 5-day forecast track for Gil.



Invest 90E

Another area of low pressure, located a few hundred miles east of Gil, continues to have a well-developed surface circulation as per last light visible satellite imagery and a 21Z microwave pass. The primary reason this system is not developing in spite of the vigor of the circulation is a lack of convection; satellite images suggest that the primary thunderstorm activity lies in a large band north of the center.



Figure 3. Latest infrared satellite image of Invest 90E. Image credit: NOAA's Satellite Services Division (SSD).

In addition, Gil appears to be producing northwesterly shear over the system, and may also be helping to inject a little bit of subsidence into the gyre, in combination with a little bit of easterly shear. The global models differ a little on the forecast upper wind pattern over the next few days, with the CMC showing less northwesterly shear, and the GFS showing more. Given current trends and the fact that Gil is still intensifying, I surmise that the GFS forecast is more likely to be correct.

Regardless, it would only take about 12 hours of persistent deep convection to lead to the formation of a tropical cyclone. Also, since the system appears to be moving more west than west-northwest, I feel some of the guidance is too far north with this system; should it continue to track farther south, it would likely escape the influence of stronger shear associated with Gil, potentially increasing the possibility of tropical cyclogenesis in a few days.

Probability of development in 48 hours: 50%


Elsewhere

The tropical Atlantic remains quiet, although the GFS and CMC ensembles have periodically suggested the possibility of lower pressures in the west African region over the next two weeks. While there are currently no consistent signals to this effect in the ensembles, and especially not the operationals, we should monitor the eastern Atlantic carefully over the next few weeks, as there are some indications within the models that the high may weaken and lift northward a bit. That would allow for a climatological northward-migration of the ITCZ, less dry air, and less trade winds. The climatological approach of the Cape Verde season is only a couple weeks away, and I do still anticipate this season will be very active, with the possibility of 8 to 10 named storms developing during the next two months.

2013 Pacific hurricane season Hurricane Gil Invest 90E

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Tropical weather analysis - July 30, 2013

By: KoritheMan, 1:23 AM GMT on July 31, 2013

Gil

Tropical Storm Gil quickly formed today. As of the latest NHC advisory (new one is due out in just under two hours), the following information was posted on the cyclone:

Wind: 40 mph, with higher gusts
Location: 12.7°N 116.1°W
Movement: WNW at 15 mph
Pressure: 1005 mb

The satellite presentation of Gil is fairly impressive, with a large curved band to the west. Microwave data throughout the day has suggested a formative mid-level eye feature with the possibility that a primitive eyewall could be attempting to form aloft. However, this feature has not been readily apparent in conventional satellite images. Convection has increased near the center, possibly signifying the beginnings of a central dense overcast.



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

For the most part, environmental conditions appear conducive for continued intensification, with very warm waters, weak vertical shear, and the small size of the circulation. One potential negative factor -- probably why the guidance is not forecasting rapid intensification -- is an area of dry air to the west of Gil on water vapor imagery; the airmass becomes particularly dry near 125W. One additional factor supporting the possibility of rapid intensification with Gil (in addition to the microwave passes) is an upper low to the north of the circulation moving west in tandem with the tropical cyclone. This ridge is forecast by the GFS to move westward in tandem with Gil for the next 48 hours while gradually weakening; the distance of the upper low is such that it will act less to shear the cyclone and more to assist in aiding its outflow. The SHIPS rapid intensification index as of 18z shows a 40% chance of an increase of 30 kt in the next 24 hours. None of the guidance forecasts to Gil to become anything more than a minimal hurricane, and even those appear to be confined to the outlying statistical guidance. Closer to the SHIPS guidance, which seems reliable in this case, my forecast assumes Gil will reach a peak of 70 kt in 72 hours; however, the intensity forecast at longer ranges could be conservative if the eye feature observed on microwave images translates down to the surface, leading to the formation of an inner core. Beyond day three, the models show westerly shear increasing, and sea surface temperatures will begin to cool. Gradual weakening is forecast at that time.

Gil is south of a mid-level ridge, and is moving west-northwestward. A blend of satellite and microwave fixes show that the cyclone more or less remains on track with the 2100Z NHC track prediction. The synoptic pattern ahead of Gil appears straightforward, with an upper low off the coast of British Columbia diving southeastward, bringing its trailing mid-level trough with it. The global models respond to this pattern by forecasting a general west-northwest motion for the next 72 hours, after which time the trough is forecast to lift and Gil is expected to turn toward the west. There could be a weak mid-level perturbation northeast of the Hawaiian Islands near the end of the period that could be capable of turning Gil northward closer to the state, but it is too early to be confident of its strength and potential impacts on the cyclone's poleward motion at those times.

Intensity forecast and positions

INITIAL 07/30 2100Z 12.7°N 116.1°W 35 KT 40 MPH
12 hour 07/31 0600Z 13.3°N 118.2°W 45 KT 50 MPH
24 hour 07/31 1800Z 13.9°N 120.6°W 50 KT 60 MPH
36 hour 08/01 0600Z 14.5°N 122.8°W 55 KT 65 MPH
48 hour 08/01 1800Z 15.3°N 125.3°W 65 KT 75 MPH
72 hour 08/02 1800Z 16.4°N 129.5°W 70 KT 80 MPH
96 hour 08/03 1800Z 16.6°N 132.4°W 60 KT 70 MPH
120 hour 08/04 1800Z 16.7°N 136.8°W 50 KT 60 MPH

Track forecast



Figure 2. My 5-day forecast track for Gil.



Invest 90E

An area of low pressure centered a few hundred miles east of Tropical Storm Gil is also quickly organizing. Satellite images show evidence of convective banding to the north, and previous microwave data hinted at this as well.



Figure 3. Latest infrared satellite image of Invest 90E. Image credit: NOAA's Satellite Services Division (SSD).

The development potential/intensity forecast for this disturbance are rather mixed. None of the guidance suggests significant intensification, and several of the global models -- including the GFS -- fail to initialize or develop it. The ECMWF, which seems to rarely develop cyclones, does show development eventually. I don't see much evidence of vertical shear over the system at the moment, but the GFS assumes that there could be some northwesterly shear in the next couple of days, likely emanating from Gil's outflow. Complicating matters further is the possibility of a Fujiwhara interaction between this disturbance and Gil. Although the circulation of Gil is small, so this one, and the former's circulation envelope appears to be healthier overall, so I presume Gil will ultimately prevail.

Regardless, conditions do appear favorable for the present time, and I expect this disturbance to become a tropical cyclone in the next 24 hours. Preliminary track guidance suggests a motion to the west-northwest, which seems consistent with current trends and the large-scale pattern.

Probability of development in 48 hours: 60%

2013 Pacific hurricane season Tropical Storm Gil Invest 90E

Updated: 1:33 AM GMT on July 31, 2013

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Tropical weather analysis - July 30, 2013

By: KoritheMan, 6:12 AM GMT on July 30, 2013

Invest 91L

A tropical wave, the remnants of Dorian, are located to the north of Hispaniola. Shower activity has increased again, but it remains disorganized; in addition, surface pressures are high, and there are no signs of a surface circulation.



Figure 1. Latest infrared satellite image of Invest 91L. Image credit: NOAA's Satellite Services Division (SSD).

The ongoing convective burst should not be taken as a sign that Dorian is trying to regenerate. There is still plenty of shear over the system, as evidenced by the rather flat outflow pattern along the west side; indeed, satellite analysis over the last several hours suggests that the upper tropospheric outflow associated with this system was actually better defined earlier, signifying another increase in shear.

Based on current and forecast trends, westerly shear is likely going to continue afflicting the system for the next 48 hours, and may actually increase a little during this time. Afterward, there is some indication that the upper flow may relax somewhat when the system reaches the Straits of Florida in three to four days, but considering the lack of a surface reflection up to this point, I question the system's ability to take advantage of this.

The wave appears to be moving westward again based on low-cloud lines from shortwave infrared satellite imagery; this could have been due to a lack of convection from a few hours ago. With the recent burst, the environmental steering favors a continued west-northwest track, north of the northern coast of Cuba, through the Florida Straits, and into the Gulf of Mexico thereafter. Since there is no well-defined center, the global models are of little practical value in this particular instance, so I relied instead upon the steering forecasts from the GFS and CMC for the next six days, which suggests the pattern over the Gulf favors the system moving into the northern or western Gulf Coast, a solution which has at times been supported by the statistical and dynamical model guidance.

The chance for redevelopment is quickly closing, and environmental conditions do not favor this system becoming a tropical cyclone again.

We may have to wait until the high weakens before we see any real development. Many active seasons in the Atlantic did not begin until the third or fourth week of August, including the volatile 1998 season, which saw Georges impact the northern Gulf Coast as a Category 2, and Mitch, which became a Category 5 and killed nearly 20,000 in Central America primarily due to floods. Things will get active, and the 500 mb pattern so far still shows no signs of budging, and favors a very active year for the United States.

Probability of development in 48 hours: 20%

Flossie

Flossie has weakened to a tropical depression, but continues to lash the Hawaiian Islands with heavy rains and tropical storm force winds. As of the latest advisory from the Central Pacific Hurricane Center, the following information was available on the tropical cyclone:

Wind: 35 mph, with higher gusts
Location: 21.3N 156.5W
Movement: WNW at 18 mph
Pressure: 1002 mb

Possibly due to slightly warmer waters along the islands -- along with orographic lift from the rugged terrain on the islands, satellite and radar data suggest a rather vigorous burst of convection. This convection is located primarily to the south of the center in a convective band, the displacement due to moderate northerly to northwesterly shear caused by an upper-level high to the north. The global models think that this shear will continue, so there is no reason to assume any restrengthening of the storm in spite of the ongoing convection, which is actually dwindling as I write this.



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

Satellite, radar, and microwave fixes indicate that Flossie continues to move toward the west-northwest, which would go well with the synoptic environmental steering. Virtually all of the guidance suggests that the storm will pass near over Kauai within the next 6 to 8 hours, and that is what I will forecast as well; however, in this particular instance, most of the associated weather does not accompany the center, so unless things change within the convective regime soon, Kauai and the remainder of the Hawaiian Islands will feel the primary effects as Flossie moves by to the north. A continued west-northwest motion is expected over the next several days, in agreement with the guidance, as Flossie approaches a break in the subtropical ridge.

The primary hazard with Flossie continues to be heavy rainfall. Doppler radar estimates have begun to show a developing swath of 2 to 4 inch rains over much of Maui County, perhaps not coincidentally after the new convective burst began around 0230 UTC. The National Weather Service office in Honolulu has issued flash flood watches for the entire archipelago, including a stray flash flood warning on the island of Maui in Maui County, incidentally where the doppler estimates showed the greatest estimated rainfall.

While the primary threat remains the potential for heavy rains and flash flooding, there have been some reports of tropical storm force wind gusts in the state, with an observing station in Kahului on Maui County recently reporting a sustained wind of 33 mph, with a gust to 46 mph in a strong rainband. These winds will likely continue as long as some semblance of convection remains; despite its weakened state, Flossie possesses a rather vigorous surface circulation, and it would not take a lot of thunderstorms to bring down strong winds aloft to the surface, especially in gusts. The wind threat will be maximized along communities in higher elevations, and will likely cause power outages and some minor tree damage.

High surf and coastal erosion will also be a significant concern.

Due to the limitations of the track map I typically use to draw tracks in this basin, I am unable to furnish a single forecast point for today, but I am in pretty good agreement with the CPHC's official track. Because of those limitations, I will not be posting an intensity forecast either, since they kind of go hand in hand.

CPHC storm information

WTPA31 PHFO 300404 CCA
TCPCP1

BULLETIN
TROPICAL DEPRESSION FLOSSIE ADVISORY NUMBER 21
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP062013
500 PM HST MON JUL 29 2013

...FLOSSIE WEAKENS TO A TROPICAL DEPRESSION JUST NORTH OF MAUI...

SUMMARY OF 500 PM HST...0300 UTC...INFORMATION
----------------------------------------------
LOCATION...21.3N 156.5W
ABOUT 145 MI...230 KM NW OF HILO HAWAII
ABOUT 90 MI...145 KM E OF HONOLULU HAWAII
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...WNW OR 290 DEGREES AT 18 MPH...30 KM/H
MINIMUM CENTRAL PRESSURE...1002 MB...29.59 INCHES


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

ALL TROPICAL STORM WARNINGS HAVE BEEN DISCONTINUED.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

THERE ARE NO WATCHES OR WARNINGS IN EFFECT.

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

DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 500 PM HST...0300 UTC...THE CENTER OF TROPICAL DEPRESSION FLOSSIE
WAS LOCATED NEAR LATITUDE 21.3 NORTH...LONGITUDE 156.5 WEST. THE
DEPRESSION IS MOVING TOWARD THE WEST-NORTHWEST NEAR 18 MPH...30
KM/H.

MAXIMUM SUSTAINED WINDS ARE NEAR 35 MPH...55 KM/H...WITH HIGHER
GUSTS. SOME WEAKENING IS FORECAST DURING THE NEXT 48 HOURS.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 1002 MB...29.59 INCHES.

HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM FORCE WIND GUSTS ARE POSSIBLE THIS EVENING AND
OVERNIGHT. LOCALLY GUSTY WINDS WILL LIKELY CONTINUE ON TUESDAY OVER
THE CENTRAL AND WESTERN ISLANDS.

RAINFALL...LOCALLY HEAVY RAINFALL IS PRESENTLY OCCURRING OVER
PORTIONS OF THE BIG ISLAND. LOCALLY HEAVY RAINFALL IS EXPECTED THIS
EVENING AND OVERNIGHT OVER MAUI COUNTY...SPREADING TO OAHU AND
KAUAI LATER TONIGHT. FLOSSIE IS EXPECTED TO PRODUCE TOTAL RAINFALL
AMOUNTS OF 2 TO 4 INCHES OVER THE BIG ISLAND WITH ISOLATED AMOUNTS
UP TO 6 INCHES. OVER THE REST OF THE STATE TOTAL RAINFALL AMOUNTS
WILL BE 1 TO 2 INCHES WITH ISOLATED AMOUNTS UP TO 6 INCHES. THIS
RAINFALL COULD CAUSE LIFE-THREATENING FLASH FLOODS AND MUD
SLIDES...ESPECIALLY IN THE MOUNTAINS.

SURF...DANGEROUS HIGH SURF WILL CONTINUE TO AFFECT EAST FACING
SHORES. THE SURF WILL BEGIN TO SUBSIDE TONIGHT ALONG EAST FACING
SHORES OF THE BIG ISLAND. LARGE SURF WILL CONTINUE ON TUESDAY FOR
THE REST OF THE STATE BEFORE SUBSIDING TUESDAY NIGHT. THE LARGE
SURF MAY CAUSE COASTAL ROAD CLOSURES.

NEXT ADVISORY...1100 PM HST.

$$
FORECASTER BURKE



Invest 99E

An area of low pressure located about 850 miles south-southwest of the southern tip of Baja California is showing signs of organization. Evening satellite images show a banding-type cloud pattern, which is normally a sign of a developing system.



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

Upper-level winds are forecast to become more conducive for development over the next couple of days, particularly beyond 24 hours when the GFS builds an upper-level anticyclone over the disturbance. There is a developing upper low off the Pacific northwest, which the models show digging southeastward over the next 48 hours; this is expected to cause a general west-northwestward motion during the next two to three days, with the possibility of a more westward-moving system thereafter as the trough lifts north and the subtropical ridge rebuilds to the north of the system. Long-range predictions suggest this system will enter the central Pacific basin over a week from now, but its potential threat to Hawaii remains uncertain.

Probability of development in 48 hours: 30%

2013 Atlantic hurricane season 2013 Pacific hurricane season Invest 91L Tropical Depression Flossie Invest 99E

Updated: 6:18 AM GMT on July 30, 2013

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Tropical weather analysis - July 29, 2013

By: KoritheMan, 7:11 AM GMT on July 29, 2013

Invest 91L

A tropical wave, the remnants of Dorian, is located about 150 miles north of Anguilla. Satellite images suggest that the associated shower activity is not well-organized. A 0z ASCAT pass caught the circulation of the tropical wave and suggested that there wasn't much of one there, with a nearly-uniform fetch of easterly winds, and no indication of a cyclonic wind shift; surface observations from Anguilla suggested the same thing.



Figure 1. Latest infrared satellite image of Invest 91L. Image credit: NOAA's Satellite Services Division (SSD).

There is still some southwesterly to westerly shear afflicting the wave, but water vapor imagery suggests the outflow pattern is much better defined than the last several days. The imagery also shows two upper lows; one near Bermuda, and the other near the Turks and Caicos. The latter feature continues to weaken, which should result in a temporary decrease in vertical shear. By Tuesday morning, however, the GFS suggests that 15 to 20 kt of westerlies will lambast the system, which is an unfavorable condition for a westward-moving system. Thereafter, if the wave can survive the shear, northerly shear is forecast to increase as a ridge builds over the eastern United States. If the system ever makes it into the Gulf of Mexico as some models suggest, the environment could become more favorable, although not anticyclonic.

Synoptic data suggest that the wave remains south of a persistent subtropical ridge. Although water vapor imagery shows the presence of an upper-level trough over the eastern United States, the global models lift this feature out, and real-time data suggests it is slowly moving out as well. Analysis of the various steering layers and forecasts of those layers suggests that, barring rapid development, movement into the Gulf of Mexico next week appears likely. Where the system goes once in the Gulf depends on the evolution of another trough forecast to amplify over the Great Lakes/southern Canada in about four days, which is impossible to determine at this point. If the trough is weaker farther north, the system may try to make its way up to the northern Gulf Coast. If not, it may attempt a strike on the western Florida peninsula region.

Regardless, until a definitive center forms (if it ever does), concentrating on any of the forecast models is of little value.

Probability of development in 48 hours: 50%

Flossie

Tropical Storm Flossie continues to move toward the Hawaiian Islands. As of the 0300Z Central Pacific Hurricane Center advisory, the following information was available on the storm:

Wind: 60 mph, with higher gusts
Location: 19.5N 151.0W
Movement: W at 8 mph
Pressure: 996 mb

It appears that Flossie is finally succumbing to the harsh synoptic environment in which it is embedded. Satellite images show a significant deterioration of the cloud pattern, with the center lying to the west of a broken convective band. Satellite estimates are correspondingly beginning to decrease. Upper-level outflow is well-defined to the north and west of the system.



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

Although areal sea surface temperature analyses indicate that Flossie will be traversing gradually warmer waters on its course toward Hawaii, the harsh thermodynamic profiles and increasing northerly shear -- depicted quite well on water vapor imagery -- argues against reintensification prior to landfall. It is entirely possible, likely so many other systems in this area, that Flossie will weaken to a tropical depression before it makes landfall; there is also the chance of dissipation, although based on the resilience of the circulation thus far, that option appears less likely at this time.

Flossie remains south of a well-established subtropical ridge, which is causing a seemingly due westward motion of the tropical cyclone. The global models have not budged, and still show a landfall along the Big Island later today (eastern time). Compared to 24 hours ago, the guidance has emanated a proclivity toward a slightly faster landfall, and that trend was closely followed for my own forecast package. After landfall, the global models show the ridge weakening a little as Flossie nears a digging upper trough now evident in water vapor imagery around 173W. Consequently, a more west-northwest motion is anticipated beyond that time. Due to the limitations of the map I use to make track forecasts, I am unable to pinpoint forecast points beyond 24 hours.

Even if Flossie weakens, the topography of the Hawaiian Islands suggests that winds at higher elevations will be significantly stronger than those experienced at ground level; these winds will be capable of causing extensive power outages and minor tree damage. Additionally, very heavy rainfall can be expected, with the possibility of 5 to 10 inches over the next 24-48 hours across the islands, which could result in flash flooding and mudslides. Very high surf and rip currents will also accompany Flossie, and are already overspreading the archipelago now.

Intensity forecast and positions

INITIAL 07/29 0600Z 19.5°N 151.5°W 50 KT 60 MPH
12 hour 07/29 1800Z 19.5°N 154.4°W 40 KT 45 MPH...NEAR THE BIG ISLAND OF HAWAII
24 hour 07/30 0600Z 19.7°N 158.1°W 35 KT 40 MPH

Track forecast



My forecast track for Flossie.

CPHC storm information

WTPA31 PHFO 290553
TCPCP1

BULLETIN
TROPICAL STORM FLOSSIE INTERMEDIATE ADVISORY NUMBER 17A
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP062013
800 PM HST SUN JUL 28 2013

...FLOSSIE CONTINUES TO BEAR DOWN ON THE MAIN HAWAIIAN ISLANDS...


SUMMARY OF 800 PM HST...0600 UTC...INFORMATION
----------------------------------------------
LOCATION...19.5N 151.0W
ABOUT 265 MI...425 KM E OF HILO HAWAII
ABOUT 465 MI...750 KM ESE OF HONOLULU HAWAII
MAXIMUM SUSTAINED WINDS...60 MPH...95 KM/H
PRESENT MOVEMENT...W OR 265 DEGREES AT 18 MPH...30 KM/H
MINIMUM CENTRAL PRESSURE...996 MB...29.41 INCHES


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

NONE.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

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

A TROPICAL STORM WATCH IS IN EFFECT FOR
*KAUAI AND NIIHAU

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

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

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


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 800 PM HST...0600 UTC...THE CENTER OF TROPICAL STORM FLOSSIE WAS
LOCATED NEAR LATITUDE 19.6 NORTH...LONGITUDE 151.0 WEST. FLOSSIE IS
MOVING TOWARD THE WEST NEAR 18 MPH...30 KM/H...AND THIS MOTION IS
EXPECTED TO CONTINUE THROUGH THE NEXT 48 HOURS.

MAXIMUM SUSTAINED WINDS ARE NEAR 60 MPH...95 KM/H...WITH HIGHER
GUSTS. SOME WEAKENING IS FORECAST DURING THE NEXT 48 HOURS.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 160 MILES...260 KM
FROM THE CENTER.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 996 MB...29.41 INCHES.


HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM CONDITIONS ARE EXPECTED TO REACH THE BIG
ISLAND LATE TONIGHT...MAUI COUNTY MONDAY MORNING AND OAHU MONDAY
NIGHT. TROPICAL STORM CONDITIONS ARE POSSIBLE ON KAUAI AND NIIHAU
MONDAY NIGHT...LASTING INTO TUESDAY.

RAINFALL...HEAVY RAINFALL IS EXPECTED TO BEGIN AS EARLY AS MONDAY
MORNING OVER HAWAII COUNTY AND MONDAY AFTERNOON OVER MAUI COUNTY...
WITH HEAVY RAIN SPREADING TO OAHU BY MONDAY NIGHT. FLOSSIE IS
EXPECTED TO PRODUCE TOTAL RAINFALL AMOUNTS OF 6 TO 10 INCHES OVER
THE BIG ISLAND AND MAUI COUNTY...WITH ISOLATED MAXIMUM AMOUNTS OF 15
INCHES POSSIBLE...MAINLY WINDWARD. RAINFALL AMOUNTS OF 4 TO 8 INCHES
ARE POSSIBLE OVER OAHU...WITH ISOLATED MAXIMUM AMOUNTS OF 12 INCHES
POSSIBLE...MAINLY WINDWARD. THIS RAINFALL COULD CAUSE LIFE-
THREATENING FLASH FLOODS AND MUD SLIDES...ESPECIALLY IN THE
MOUNTAINS.

SURF...DANGEROUSLY HIGH SURF IS STARTING TO HAMMER EAST FACING
SHORES OF THE BIG ISLAND. SURF WILL BUILD OVERNIGHT...WITH THE
LARGEST SURF EXPECTED MONDAY INTO TUESDAY. THE BIG SURF MAY CAUSE
COASTAL ROAD CLOSURES...EVEN BEFORE THE STORM ARRIVES. PLEASE SEE
THE LATEST HURRICANE LOCAL STATEMENT FOR INFORMATION SPECIFIC TO
YOUR AREA.

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

$$
FORECASTER DONALDSON

2013 Atlantic hurricane season 2013 Pacific hurricane season Invest 91L Tropical Storm Flossie

Updated: 7:16 AM GMT on July 29, 2013

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Tropical weather analysis - July 28, 2013

By: KoritheMan, 5:59 AM GMT on July 28, 2013

Flossie

Tropical Storm Flossie continues to move westward across the central Pacific:

Wind: 50 mph, with higher gusts
Location: 19.0N 143.2W
Movement: W at 20 mph
Pressure: 1000 mb

Although Flossie has already crossed the 26C isotherm, convection has increased again, with a distinct curved band in the western semicircle. In addition, there does not appear to be any substantial vertical shear over the system, with the GFS actually suggesting that the shear will not increase over the storm until about 36-48 hours.



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

The models suggest continued weakening on a gradual basis, but this will likely not come from vertical shear in the immediate future. However, water vapor imagery shows an enormous amount of subsidence ahead of the cyclone, and the SHIPS responds to this by forecasting a continued decrease in relative humidity values. The combination of dry air, cool water temperatures, and then increasing westerly shear as Flossie approaches the Hawaiian Islands should cause the cyclone to slowly weaken. Areal sea surface temperature analyses indicates that sea surface temperatures warm in the vicinity of the Hawaiian Islands, so it is likely that Flossie will maintain at least minimal tropical storm strength as it makes landfall on the Big Island on Monday evening.

Flossie is south of a well-established mid-level ridge over the central Pacific. Water vapor images suggest a lot of zonal flow developing to the north of the Hawaiian Islands, a similar signature of which was confirmed in recent UW-CIMSS steering analyses. This implies a strengthening of the ridge, so Flossie is likely to turn due west near 150W. Virtually all of the guidance takes Flossie over the Big Island on Monday evening. The GFS and ECMWF have come into better agreement on the timing, which increases confidence in the forecast track.

A tropical storm watch has been issued for Hawaii and Maui counties, and interests in the watch area should begin preparation for tropical storm force winds, power outages, and very heavy rains capable of causing flash flooding. The winds could be especially dangerous in higher elevations, perhaps up to 60 mph in some of the heavier squalls.

5-day intensity forecast

INITIAL 07/28 0300Z 45 KT 50 MPH
12 hour 07/28 1200Z 45 KT 50 MPH
24 hour 07/29 0000Z 40 KT 45 MPH
36 hour 07/29 1200Z 35 KT 40 MPH
48 hour 07/30 0000Z 35 KT 40 MPH...INLAND

I am experimenting with making my track maps look more professional and less sloppy. Since I'm still learning how to use this new program I found to make them, I will withhold on carving such a map for tonight. However, my forecast track is pretty well in line with that of the Central Pacific Hurricane Center, except a bit farther south at longer ranges, taking it over the central portion of the Big Island in 48 hours.

CPHC storm information

WTPA31 PHFO 280232
TCPCP1

BULLETIN
TROPICAL STORM FLOSSIE ADVISORY NUMBER 13
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP062013
500 PM HST SAT JUL 27 2013

...FLOSSIE CONTINUES MOVING WESTWARD TOWARD THE STATE OF HAWAII...

SUMMARY OF 500 PM HST...0300 UTC...INFORMATION
----------------------------------------------
LOCATION...19.0N 143.2W
ABOUT 775 MI E OF HILO HAWAII
MAXIMUM SUSTAINED WINDS...50 MPH
PRESENT MOVEMENT...W OR 275 DEGREES AT 20 MPH
MINIMUM CENTRAL PRESSURE...1000 MB...29.53 INCHES


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

A TROPICAL STORM WATCH HAS BEEN ISSUED FOR HAWAII AND MAUI COUNTIES.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

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

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


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 500 PM HST...0300 UTC...THE CENTER OF TROPICAL STORM FLOSSIE WAS
LOCATED NEAR LATITUDE 19.0 NORTH...LONGITUDE 143.2 WEST. FLOSSIE IS
MOVING TOWARD THE WEST NEAR 20 MPH...AND THIS MOTION IS EXPECTED TO
CONTINUE FOR THE NEXT 24 TO 48 HOURS.

MAXIMUM SUSTAINED WINDS ARE NEAR 50 MPH WITH HIGHER GUSTS. SOME
WEAKENING IS FORECAST DURING THE NEXT 48 HOURS.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 175 MILES FROM THE
CENTER.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 1000 MB...29.53 INCHES.


HAZARDS AFFECTING LAND
----------------------
RAINFALL...HEAVY RAINFALL MAY BEGIN AS EARLY AS MONDAY MORNING OVER
HAWAII COUNTY AND MONDAY AFTERNOON OVER MAUI COUNTY.

WIND...TROPICAL STORM FORCE WINDS ARE EXPECTED AS EARLY AS MONDAY
AFTERNOON.

SURF...LARGE SURF WILL IMPACT EAST FACING SHORES POSSIBLY AS EARLY
AS SUNDAY AFTERNOON WITH THE LARGEST SURF EXPECTED ON MONDAY.


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

$$
FORECASTER BURKE

2013 Pacific hurricane season Tropical Storm Flossie

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Tropical weather analysis - July 26, 2013

By: KoritheMan, 1:30 AM GMT on July 27, 2013

Dorian

Tropical Storm Dorian continues to move across the central Atlantic:

Wind: 45 mph, with higher gusts
Location: 17.8°N 45.8°W
Movement: W at 22 mph
Pressure: 1010 mb

The strong subtropical ridge in place over the Atlantic has claimed another victim in 2013. Convection has essentially vanished, with only a few patchy showers remaining in a broken squall to the north. An earlier ASCAT pass around 1200 UTC suggested that Dorian was still carrying winds of tropical storm force to the north of the circulation, and the fast forward motion of the cyclone may actually assist in maintaining those winds for a little while longer, even in the absence of deep convection. As is expected to be the case with a westward-moving system at or above 20 mph, the pass showed an almost complete lack of wind to the south side of the center; several scatterometer passes throughout the day give fairly convincing evidence that Dorian no longer possesses a well-defined surface circulation, and last light visible imagery a couple hours suggested that if a circulation still does exist, it is extremely tight.



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

Satellite pictures show arc clouds emanating westward away from the center, which suggests that Dorian is still ingesting dry air. Water vapor imagery suggests that Dorian has essentially reached the axis of the driest air in the Atlantic basin, and if it somehow -- and quite miraculously -- survives for the next 24 hours, it will move into a more moist environment. I was tempted to forecast almost immediate dissipation, but I am not confident enough to do that, and I would rather maintain some continuity with my previous forecast. In about 72 hours, the global models still show an increase in shear as Dorian moves north of Puerto Rico; the mid-oceanic trough responsible for this is clearly visible on water vapor imagery, as it has been for the last several days. While upper-level winds could improve if Dorian reaches the Caribbean or the Bahamas, they will still not be ideal, and even if they were, there would likely be very little left of the system by that time to assume advantage in such an environment. I am forecasting Dorian to dissipate in about 96 hours, although it is likely to occur much, much sooner.

Dorian remains south of a well-established mid-level ridge. Although an upper-level low pressure system is in the process of amplifying over the Great Lakes, a solution well-advertised by the global models over the last few days, the cyclone is too weak to follow the mid- to upper-level flow and respond to this weakness. A general westward to west-northwestward motion is anticipated throughout the remainder of the forecast period as Dorian is steered primarily by the low-level flow.

5-day intensity forecast and positions

INITIAL 07/26 2100Z 17.8°N 45.8°W 40 KT 45 MPH
12 hour 07/27 0600Z 18.3°N 49.2°W 35 KT 40 MPH
24 hour 07/27 1800Z 18.6°N 52.5°W 30 KT 35 MPH
36 hour 07/28 0600Z 18.9°N 56.3°W 30 KT 35 MPH
48 hour 07/28 1800Z 19.4°N 60.4°W 30 KT 35 MPH
72 hour 07/29 1800Z 19.5°N 67.6°W 30 KT 35 MPH
96 hour 07/30 1800Z...DISSIPATED

5-day track forecast



Figure 2. My 5-day forecast track for Dorian.

Flossie

Tropical Storm Flossie continues to move toward the central Pacific:

Wind: 60 mph, with higher gusts
Location: 16.5°N 134.1°W
Movement: WNW at 20 mph
Pressure: 999 mb

There has been little change to the cloud pattern over the last several hours, and an ASCAT pass around 1800 UTC showed a wide swath of believable 40 to 45 kt winds, primarily in the northern portion of the circulation; given the well-documented low bias of this instrument, Flossie is likely still producing winds of around 50 kt.



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

Flossie will soon cross the 26C isotherm, and while convection may decrease some thereafter, the global models do not show westerly shear increasing until Flossie is well into the central Pacific. I don't see much evidence of westerly upper-tropospheric flow getting ready to bite on the system in water vapor imagery, which gives some credibility to the model forecasts of a later arrival of vertical shear. While a steady weakening is forecast throughout the forecast period, waters actually warm the closer you get to Hawaii, so a rare landfalling tropical cyclone on those islands seems like a distinct possibility, and it is what I will forecast at this time pending evidence to the contrary.

Satellite and microwave fixes this evening indicate that Flossie is pretty much on track with the 21Z NHC forecast, moving west-northwest to the south of a strong subtropical high. The model consensus has not changed appreciably, and Flossie is still expected to turn westward at longer ranges as the ridge strengthens, probably in the vicinity of 145W. This pattern favors an eventual landfall on the Big Island of Hawaii. There are some forward speed differences, with the GFS being faster and the ECMWF being slower. My forecast favors the former, and is also strongly in line with the forecast from the National Hurricane Center.

Tropical storm watches and warnings may be required for portions of the Hawaiian Islands during the next 24 hours, and interests there should monitor the progress of Flossie.

Even if Flossie does survive as a tropical cyclone and goes on to impact those islands, the primary threat will be heavy rains capable of causing flooding, high surf, and tropical storm force winds, particularly along higher elevations. These winds could cause power outages.

5-day intensity forecast and positions

INITIAL 07/26 2100Z 16.5°N 134.1°W 50 KT 60 MPH
12 hour 07/27 0600Z 17.3°N 137.3°W 50 KT 60 MPH
24 hour 07/27 1800Z 18.0°N 140.5°W 45 KT 50 MPH
36 hour 07/28 0600Z 19.0°N 144.0°W 40 KT 45 MPH
48 hour 07/28 1800Z 19.6°N 147.5°W 40 KT 45 MPH
72 hour 07/29 1800Z 19.6°N 153.6°W 35 KT 40 MPH
96 hour 07/30 1800Z 19.6°N 157.9°W 30 KT 35 MPH

5-day track forecast



Figure 4. My 5-day forecast track for Flossie. My forecast points do not go out to 120 hours because the map I use to draw my forecast maps don't exceed to the more westward longitude Flossie would arrive at in 120 hours.

2013 Atlantic hurricane season 2013 Pacific hurricane season Tropical Storm Dorian Tropical Storm Flossie

Updated: 1:39 AM GMT on July 27, 2013

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Tropical weather analysis - July 26, 2013

By: KoritheMan, 6:37 AM GMT on July 26, 2013

Dorian

Tropical Storm Dorian continues to march across the central Atlantic. As of the 0300Z advisory from the National Hurricane Center, the following information was available on the storm:

Wind: 50 mph, with higher gusts
Location: 16.6°N 39.6°W
Movement: WNW at 20 mph
Pressure: 1001 mb

I am having a deja vu. In a fashion similar to Chantal a few weeks ago, Dorian's low-level center appears to be becoming exposed to the west of the convection, confirmed by satellite and microwave imagery. Since there does not appear to be any large-scale vertical shear nearby that would cause this, it is likely that the fast forward motion is creating some westerly to southwesterly shear over the storm. Although convection has been increasing a bit as the cyclone approaches the diurnal convective maximum, both the microwave data and satellite images suggest that this convection is not well-organized, with no evidence of banding features. Interestingly, a 0z ASCAT pass suggested that Dorian retains a very well-defined surface circulation, and I sincerely doubt the inner core has weakened rapidly in just a few hours since the pass.



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

The intensity forecast is quite problematic, to say the least. Water vapor imagery shows dry air to the east and northeast of Dorian, and shows fast upper-level northeasterly to easterly winds associated with the unusually strong subtropical ridge anchored to the north of the system. This could cause an increase in dry air into the inner core, although there is no sign of this yet as I can tell. In about three days, as Dorian approaches the Lesser Antilles, the global models forecast an increase in westerly shear as Dorian approaches the mid-oceanic trough, which is quite well-defined on water vapor images at this time. Considering that the high is not forecast to abate anytime soon -- and may actually strengthen a little, Dorian is unlikely to slow down over the next few days. Given these factors, it is entirely possible that Dorian will lose its status a tropical cyclone at any point during the forecast period, possibly sooner rather than later given current trends. The global models generally do not initialize Dorian as a distinct tropical cyclone, with only the GFS doing so, and even that model sends Dorian southwestward into the eastern Caribbean at longer ranges, all the while losing its status as a tropical cyclone. Given the large uncertainty, I will maintain Dorian as a steady-state tropical cyclone throughout the forecast period.

Dorian remains south of a well-established mid-level ridge, rather anomalously strong for late July. Again, the global models maintain this ridge and even build it westward with time. Compared to 24 hours ago, the model consensus has shifted significantly southward, by at least 150 miles, and there have been even larger shifts within some of the individual global models, particularly the GFS.

With the GFS and ECMWF sending Dorian southward at longer ranges, and the model consensus moving southward as well, I have no choice but to go along with that. There is still considerable uncertain on Dorian's future track, and the models are clearly not handling this system very well.

Should the upper-level winds somehow improve as Dorian approaches the islands, it may very well survive beyond five days, counteracting the speed shear.

It should be noted that, unlike the typical case for tropical cyclones, the deep-layer steering does not differ much from the low-level steering, as denoted by analysis of CIMSS data and the global model forecast steering fields; this attests to the unusually strong nature of the subtropical ridge this year. Thus, Dorian won't gain appreciable poleward momentum even if it miraculously becomes stronger, and vise versa.

Interests in the Lesser Antilles should monitor the progress of Dorian in case it survives as a tropical cyclone.

5-day intensity forecast and positions

INITIAL 07/26 0600Z 17.1°N 40.1°W 45 KT 50 MPH
12 hour 07/26 1800Z 17.5°N 42.5°W 45 KT 50 MPH
24 hour 07/27 0600Z 18.0°N 45.0°W 45 KT 50 MPH
36 hour 07/27 1800Z 18.3°N 50.0°W 45 KT 50 MPH
48 hour 07/28 0600Z 19.0°N 54.9°W 45 KT 50 MPH
72 hour 07/29 0600Z 19.8°N 60.3°W 45 KT 50 MPH
96 hour 07/30 0600Z 20.3°N 65.3°W 45 KT 50 MPH
120 hour 07/31 0600Z 20.3°N 72.7°W 45 KT 50 MPH

5-day track forecast



Figure 2. My 5-day forecast track for Dorian.



Flossie

Tropical Storm Flossie continues moving toward the central Pacific. As of the latest NHC advisory, the following information was available on the system:

Wind: 45 mph, with higher gusts
Location: 15.1°N 129.0°W
Movement: W at 17 mph
Pressure: 1002 mb

Convection had decreased earlier in the day, but has rebounded over the last couple hours. With the diurnal maximum yet to plateau in this area, Flossie could strengthen a little over the next 24 hours, and my forecast will reflect that. The center is difficult to locate, but appears to be on the southern edge of the convection. An ASCAT pass around 1800 UTC Thursday indicated the low-level center was not well-defined on the south side, with a uniform fetch of southeasterly winds; it is likely that this instrument is having difficulty resolving the large-scale easterly low-level flow within that region, so little weight was placed on it.



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

Flossie is expected to cross the 26C isotherm in about 36 hours, concurrent with a slight increase in westerly shear as suggested by the global models. Thus, a weakening trend is expected by that time. By day five, Flossie will probably degenerate into a remnant area of low pressure as denoted by the guidance.

The tropical storm appears to be moving pretty much due west based on analysis of shortwave infrared satellite images this evening, which would also go well with the latest UW-CIMSS steering map. However, this motion is expected to be short-lived due to an upper low to the northwest of the cyclone, which is creating a weakness in the subtropical ridge to the north. The global models suggest a general west-northwestward motion until Flossie enters the central Pacific, at which time a more westward motion is shown as the cyclone becomes shallower and follows the low-level flow of the trade winds. While my forecast track takes Flossie very near the Big Island of Hawaii at five days, I strongly believe the cyclone will be a remnant low at that time. Regardless of its technical status when it reaches the longitude of the Hawaiian Islands, Flossie is expected to produce locally high surf, heavy rain, and strong gusty winds.

5-day intensity and positions

INITIAL 07/26 0600Z 15.5°N 129.7°W 40 KT 45 MPH
12 hour 07/26 1800Z 15.8°N 132.1°W 45 KT 50 MPH
24 hour 07/27 0600Z 16.5°N 135.2°W 45 KT 50 MPH
36 hour 07/27 1800Z 16.8°N 137.7°W 40 KT 45 MPH
48 hour 07/28 0600Z 17.8°N 142.8°W 35 KT 40 MPH
72 hour 07/29 0600Z 19.7°N 148.3°W 30 KT 35 MPH
96 hour 07/30 0600Z 19.9°N 151.1°W 30 KT 35 MPH
120 hour 07/31 0600Z 19.9°N 154.5°W 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW

5-day track forecast



Figure 4. My 5-day forecast track for Flossie.

2013 Atlantic hurricane season 2013 Pacific hurricane season Tropical Storm Dorian Tropical Storm Flossie

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Tropical weather analysis - July 25, 2013

By: KoritheMan, 6:24 AM GMT on July 25, 2013

Dorian

Tropical Storm Dorian continues to move across the open Atlantic Ocean. As of the most recent (0300Z) advisory from the National Hurricane Center, the following information was available on the cyclone:

Wind: 50 mph, with higher gusts
Location: 15.1°N 33.2°W
Movement: WNW at 20 mph
Pressure: 1002 mb

The satellite signature of Dorian is fairly impressive, especially considering the marginal sea surface temperatures that the cyclone is traversing. An AMSUB pass caught the circulation just before 0z, and showed tightly-coiled banding, but no evidence of an eye or eyewall; unfortunately, there have been no recent reliable microwave passes since then. Conventional satellite images also suggest that Dorian is a small tropical cyclone that possesses tightly-wound banding features.



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

Since Dorian has a rather large moisture envelope and an accompanying upper-level anticyclone, it appears that it will effectively ward off the otherwise detrimental influence of the cooler underlying waters; in addition, the relatively fast forward speed of the tropical storm suggests that cold water upwelling -- normally quite significant over this area of the Atlantic -- will not be a factor. Given this, the most appropriate forecast at this time seems to be to forecast a steady-state storm until water temperatures rebound to 27C near the 72 hour mark. Beyond that time, some slight reintensification is shown, although I am choosing to be conservative with the intensity at longer ranges, since water vapor images still show a rather large area of dry air, albeit propagating westward in tandem with Dorian, over the central Atlantic; also, the global models still forecast an increase in westerly shear during that time as Dorian nears the mid-oceanic trough. Given these factors and the small size of the storm, Dorian could easily dissipate or be a hurricane at the end of the forecast period.

Dorian is embedded within a well-established mid-level ridge over the central Atlantic. This ridge is forecast to elongate and build westward ahead of Dorian during the next several days, which is not expected to cause immediate recurvature. Whether or not Dorian ultimately makes United States landfall at longer ranges is still extremely uncertain, and we probably won't have a better idea for at least another four or five days. The global models show a large and well-defined upper low amplifying over the Great Lakes in about 96 hours, which is anticipated to weaken the western extent of the subtropical ridge over the western Atlantic. However, that feature appears very fragile, and will not be enough to recurve Dorian. A second piece of shortwave energy is forecast to dive from Canada into the northern United States beyond 7 days, which will reinforce the weakness in the ridge. It is this secondary shortwave pulse that we will need to monitor over the coming days, as the amplitude and progression of that feature is critical to determining when, where, or if Dorian makes United States landfall at longer ranges, ranges that go far beyond the scope of my 5-day forecast.

At this time, the pattern seems more supportive of an east coast storm than a Gulf coast storm, and I am reminded of Hurricane Floyd in 1999, albeit at much lesser intensities.

Regardless, the Lesser Antilles are first in line, and, although Dorian is forecast to pass to the north of those islands and Puerto Rico, interests in those areas should continue to monitor the progress of this tropical cyclone.

5-day intensity and forecast positions

INITIAL 07/25 0300Z 15.1N 33.2W 45 KT 50 MPH
12 hour 07/25 1200Z 15.7N 35.1W 45 KT 50 MPH
24 hour 07/26 0000Z 16.3N 39.8W 45 KT 50 MPH
36 hour 07/26 1200Z 16.8N 43.5W 45 KT 50 MPH
48 hour 07/27 0000Z 17.5N 46.4W 45 KT 50 MPH
72 hour 07/28 0000Z 18.9N 53.7W 50 KT 60 MPH
96 hour 07/29 0000Z 19.5N 59.7W 50 KT 60 MPH
120 hour 07/30 0000Z 19.7N 65.8W 50 KT 60 MPH

5-day track forecast



Figure 2. My 5-day forecast track for Dorian.

Invest 99L

A non-tropical area of low pressure is located several hundred miles east of Bermuda. Scatterometer and satellite data suggest that the circulation is poorly-defined, but there is a healthy burst of convection ongoing, likely assisted by upper-level diffluence associated with a small and elongated upper low to the west.



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

Despite the unimpressive nature of the circulation, waters appear sufficiently warm for some development during the next 24-36 hours, and there appears to be no significant vertical shear over the system; in fact, the upper flow might actually be southerly in connection with said upper low, a pattern which could support development of a northward-moving system like 99L.

This low is forecast to become absorbed in a frontal zone in about two days.

Probability of development in 48 hours: 20%

Tropical Depression Six-E

Tropical Depression Six-E formed on Wednesday evening from what was previously Invest 98E. As of the latest NHC advisory, the following information was posted on the system:

Wind: 35 mph, with higher gusts
Location: 15.2°N 122.0°W
Movement: WNW at 14 mph
Pressure: 1005 mb

An ASCAT pass from around 1800 UTC Wednesday showed winds already in excess of tropical storm force, so perhaps the NHC will recognize an earlier classification of this system during post-season analysis.

Satellite images show a large and expansive burst of very cold convection, with the center presumed to be roughly in the center of this activity.



Figure 4. Latest infrared satellite image of Tropical Depression Six-E. Image credit: NOAA's Satellite Services Division (SSD).

There still appears to be some northeasterly shear over the system, as the outflow pattern appears squashed in that direction. Other than that, conditions appear favorable for some strengthening, and the depression is forecast to become a tropical storm very soon, if it is not already one. If the system had a little more time, it would probably become a hurricane, but alas, the cyclone is forecast to move into colder waters in about 36 hours, so steady weakening is anticipated beyond that time. The models show westerly shear increasing as the system crosses the central Pacific on Saturday, so the weakening I am projecting is a little more rapid at days four and five than that of the National Hurricane Center.

Although the global models show this system reaching the Hawaiian Islands early next week, waters are not going to warm along the current forecast track, so if anything does reach that area, it is very likely to be nothing more than a showery remnant low capable of disrupting the local trade wind flow.

The dynamical models are in good agreement on an undulating west-northwestward track for the next 72 hours, followed by the possibility of a more westward turn beyond that time as the system comes under the influence of the low-level flow as it becomes a vertically shallower system.

5-day intensity and forecast positions

INITIAL 07/25 0300Z 15.2N 122.0W 30 KT 35 MPH
12 hour 07/25 1200Z 15.5N 123.5W 40 KT 45 MPH
24 hour 07/26 0000Z 16.1N 127.1W 45 KT 50 MPH
36 hour 07/26 1200Z 17.3N 130.5W 50 KT 60 MPH
48 hour 07/27 0000Z 18.7N 134.7W 45 KT 50 MPH
72 hour 07/28 0000Z 20.1N 140.0W 40 KT 45 MPH
96 hour 07/29 0000Z 20.7N 144.2W 30 KT 35 MPH
120 hour 07/30 0000Z 20.8N 149.2W 25 KT 30 MPH

5-day track forecast



Figure 5. My 5-day forecast track for TD Six-E.

2013 Atlantic hurricane season 2013 Pacific hurricane season Tropical Storm Dorian Invest 99L Tropical Depression Six-E

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Tropical weather analysis - July 24, 2013

By: KoritheMan, 9:10 AM GMT on July 24, 2013

Tropical Depression Four

The strong tropical wave we have been tracking over the eastern Atlantic has developed sufficient organization to be classified as a tropical depression. According to the latest NHC advisory, the following information was available on the newly-developed cyclone:

Wind: 35 mph, with higher gusts
Location: 13.9°N 28.1°W
Movement: WNW at 20 mph
Pressure: 1008 mb

Satellite images show an impressive burst of cold-topped convection, with a recent SSMIS pass suggesting the center is located within the northern portion of this burst. An earlier ASCAT pass from just before 0z showed a very well-defined surface circulation, and believable winds of 30 kt in the northeastern quadrant of the cyclone circulation.



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

The depression is currently under light upper tropospheric easterly to northeasterly shear, which is typical for Cape Verde systems. However, the system will be traversing cooler waters today, crossing the 26C isotherm in roughly 12 hours; this is expected to inhibit short-term intensification despite light upper tropospheric vertical shear prospects. By 72 hours, the cyclone is forecast to move into warmer waters, and some reintensification is shown during that portion of the forecast period. It should be noted that there are some rather mixed signals in the global models regarding the long-term evolution of the upper-level winds ahead of the depression, with the 0z GFS showing more shear than in earlier runs, presumably because it takes the depression a little farther north into the core of stronger westerlies. Water vapor imagery does show a quasi-stationary baroclinic zone/upper trough over the central Atlantic, which is likely the cause of the shear within the models. As long as the cyclone can remain south of 20N, it should have a fair shot at surviving, at least a very weak and struggling system. The global models do not show much intensification, while the statistical models are a little more aggressive, showing the system becoming a mid-range tropical storm.

The shear could decrease as the system nears the Lesser Antilles in five days, but there is too much uncertainty at those time ranges to justify basing my intensity forecast off that possibility. The farther south the depression tracks, the less the magnitude of the shear. I do not currently anticipate this system becoming a hurricane, and it is still a little early for a serious land threat according to climatology.

The depression is moving west-northwest to the south of a well-established mid-level ridge. The global models show this ridge building westward ahead of the depression with time, which should impart a more westward motion in about three days. The models are in good agreement with this general pattern evolution, and even the historically reliable ECMWF, which was previously forecasting recurvature, now takes the system considerably farther south and west on the 0z run. I am not willing to speculate on the track beyond the longitude of the Lesser Antilles, but interests there should monitor the progress of the depression, as it could bring heavy rain and tropical storm force winds to that area if it survives.

I do not currently see TD Four being a huge threat, but rather a harbinger of what is likely to be a much more dangerous August and September for much of the basin.

5-day intensity forecast and positions


INITIAL 07/24 0900Z 30 KT 35 MPH 13.9N 28.1W
12 hour 07/24 1800Z 35 KT 40 MPH 14.4N 30.3W
24 hour 07/25 0600Z 35 KT 40 MPH 15.1N 33.7W
36 hour 07/25 1800Z 35 KT 40 MPH 15.9N 36.8W
48 hour 07/26 0600Z 35 KT 40 MPH 17.3N 40.8W
72 hour 07/27 0600Z 40 KT 45 MPH 18.8N 49.5W
96 hour 07/28 0600Z 45 KT 50 MPH 18.9N 55.0W
120 hour 07/29 0600Z 45 KT 50 MPH 19.3N 62.7W

5-day track forecast



Figure 2. My 5-day forecast track for TD Four.

2013 Atlantic hurricane season Tropical Depression Four

Updated: 9:13 AM GMT on July 24, 2013

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Tropical weather analysis - July 23, 2013

By: KoritheMan, 3:28 AM GMT on July 24, 2013

Invest 98L

A vigorous tropical wave and associated surface low pressure system is located about 150 miles southwest of the Cape Verde Islands. The second tropical wave in a row to defy Atlantic basin climatology this year, satellite, microwave, and scatterometer data show a small but well-defined surface circulation. Convection has increased directly over the center in a small thunderstorm burst. In addition, there is evidence of curved banding to the south, which may attempt to wrap up into the center overnight and increase the overall organization of the system.



Figure 1. Latest infrared satellite image of Invest 98L. Image credit: NOAA's Satellite Services Division (SSD).

Although upper-level winds are relatively favorable, satellite analysis this evening suggests that 98L has begun to move more toward the west-northwest, which is in contrast to 24 hours ago when the motion was pretty much due west; this is probably more related to a local weakness in the subtropical ridge rather than any large scale low pressure system signaling the start of recurvature. There continues to be no evidence that would suggest anything close to what the models were seeing a couple of days ago, when they were pretty much unanimously taking it above 20N before the system even got near 60W.

In the interim, however, the observed west-northwestward motion will take the system over the 26C isotherm in about 18-24 hours; the associated atmospheric stability triggered by those cool waters will likely halt the intensification process. A decent analog for a storm in this area would be Hurricane Bertha in 2008, which also formed in July, and did not immediately intensify due to a similar patch of cooler waters. It took Bertha until around 45 to 50W to begin ramping up as it escaped the influence of those waters, and that is what I would anticipate occurring with 98L, with significant intensification not beginning until then.

The SHIPS model and SST diagrams of the area indicate that 98L may gradually escape the influence of these cooler waters, the waters warming to 27C by 72 hours according to the 0z SHIPS file. If the system can survive the meager thermodynamic environment in the eastern Atlantic associated with the cooler waters, it will have an opportunity to intensify at longer ranges. The GFS is showing considerably less shear than a couple of days ago, particularly if the system remains south of 20N, which based on the guidance and current trends, I am expecting to happen; the 18Z GFS showed very little zonal shear over the system throughout the next five days, and the system only lost its anticyclonic support when it died a painful death over the mountains of Hispaniola.

It is far too early to speculate on the long-range track prospects, but interests in the Cape Verde Islands will experience gusty winds and locally heavy rainfall, even if the system does not become a tropical cyclone overnight. Interests in the Lesser Antilles should also monitor the progress of this disturbance, as it could pay that area a visit on Sunday or Monday, particularly the central and northern islands. The ECMWF and UKMET still suggest a trajectory out to sea, but there have been some hints in the remainder of the models that the ridge will amplify and build westward over the central and western Atlantic in tandem with 98L's westward progression, which seems to be more believable option lacking any real weakness in the Atlantic subtropical ridge at the present time. Given the reliability of the ECMWF, however, the out to sea scenario still cannot be discounted, although I expect this model will come southward over the next couple of days. I personally favor a more west-northwest track over the next 48-72 hours, with a gradual turn back toward the west at those ranges.

Assuming the current rate of organization continues, I expect a renumber in the ATCF file to Tropical Depression Four or Tropical Storm Dorian for the tentative 5 AM NHC advisory. While some have speculated on dissipation of this system amidst the cool waters, lacking any substantial vertical shear to assist the cool waters in dismantling the system, I honestly find the solution of this system dying pretty unrealistic; it'll more likely remain steady state for the next few days before reintensifying beyond 72 hours.

Probability of development in 48 hours:
80%

Invest 98E

A broad area of low pressure over the Pacific located about 900 miles south-southwest of the southern tip of Baja California has not become any better organized over the last 24 hours. The circulation still appears to be poorly-defined, with no evidence of northerly or westerly winds along the western half of the circulation that would signify the beginnings of a closed surface circulation. There is more convection today than yesterday, but a lot of it appears to be associated with upper diffluence in connection with an upper low to the northwest, and the convection exhibits little curvature, and is actually rather shapeless at the moment.



Figure 2. Latest infrared satellite image of Invest 98E. Image credit: NOAA's Satellite Services Division (SSD).

Nevertheless, there are finally some signs that the storm-relative vertical shear is beginning to decrease a little, and the system could still develop a bit before it reaches cooler waters beyond 48 hours. I do not anticipate 98E ever becoming a tropical cyclone.

98E is not a threat to land, and the aforementioned upper low will take it a on west-northwest trajectory into the central Pacific, where it will ultimately dissipate.

Probability of development in 48 hours: 30%

2013 Atlantic hurricane season 2013 Pacific hurricane season Invest 98L Invest 98E

Updated: 3:30 AM GMT on July 24, 2013

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Tropical weather analysis - July 23, 2013

By: KoritheMan, 5:24 AM GMT on July 23, 2013

Invest 98L

A vigorous tropical wave accompanied by a surface area of low pressure is centered about 250 miles southeast of Sal in the Cape Verde Islands. This wave has been designated "Invest 98L" by the National Hurricane Center.

Yet again we have another unusually strong tropical wave for so early in the season. Satellite images show an impressive amount of rotation, and the low-level center of 98L appears to be embedded within the cloud mass just east of the deepest convection.



Figure 1. Latest infrared satellite image of Invest 98L. Image credit: NOAA's Satellite Services Division (SSD).

Upper-level winds appear favorable for additional development. However, there are some hurdles, short-term and long-term, that could ultimately mitigate significant development of 98L even if it becomes a tropical cyclone. Firstly, most of the models are forecasting a west-northwest track, probably in response to an upper low to the northwest of the system as seen on water vapor imagery. While this low appears quasi-stationary for the moment, it is predicted to move westward and weaken; even if there is a residual weakness within the cyclonic vorticity connected with that feature after it weakens, it is unclear how much short-term latitude 98L will gain. The motion for the last twelve hours appears to be due west, and I don't see any convincing evidence of an appreciable low- to mid-tropospheric weakness until around 45W. It is my personal expectation that 98L will move generally westward for the next day or two before it moves closer to the apex of the central Atlantic trough, at which point I expect some latitude gain, attendant with a west-northwest motion.

Considering the above factors, I expect the dynamical model suite to shift southward over the next 24 hours; indeed, there has already been an observed southward shift in that suite from 18z to 0z. I do not currently expect 98L to be a Caribbean cruiser based on the pattern, but I am not buying an immediate west-northwest motion as the models are advertising. 98L is also embedded within a convectively active monsoon trough, and it is possible there could be some erratic motion at times, deviating from the overall mean.

Back to what I was saying earlier about intensity, the enunciated west-northwestward motion seen in the model fields would take the system over cooler waters sooner, probably in less than 48 hours. In addition, the models show a large increase in westerly shear beyond 48 hours as the wave moves closer to the central Atlantic upper trough. If the system were to track farther south, particularly below 20N, the shear would be much less, the waters would stay warm, and the system would have more potential to strengthen. It is my expectation that 98L will remain over waters that are at least marginal through the next couple of days, which should allow some additional development.

It is too early to tell whether or not 98L recurves. Based on the current pattern and the one forecast to evolve in the model fields, a system that gains latitude quicker over the next several days may recurve, but a system that more subtly gains latitude may not. This could also be irrelevant if 98L dies a cruel death under strong vertical shear.

At the risk of completely blowing the forecast, I am going much higher with development percentages than the National Hurricane Center.

Probability of development in 48 hours: 60%

Invest 98E

An area of low pressure located about 550 miles southwest of Manzanillo, Mexico is producing disorganized showers and thunderstorms.

Analysis of satellite imagery this evening reveals that the disturbance hasn't really gotten any better organized, and there appears to be some northeasterly shear affecting the system.



Figure 2. Latest infrared satellite image of Invest 98E. Image credit: NOAA's Satellite Services Division (SSD).

Earlier scatterometer fixes and microwave data suggest that the low-level center is poorly-defined, as does satellite imagery. The models insist that upper-level winds will gradually become more favorable, so I have no choice but to forecast some development. The system is not forecast to threaten land, and it will encounter cooler waters in about four days.

Probability of development in 48 hours: 30%

2013 Atlantic hurricane season 2013 Pacific hurricane season Invest 98L Invest 98E

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Tropcial weather analysis - July 10, 2013

By: KoritheMan, 6:22 AM GMT on July 10, 2013

Chantal

Tropical Storm Chantal continues to race across the central Caribbean Sea. As of the latest NHC advisory, the following information was available on the storm:

Wind: 50 mph, with higher gusts
Location: 15.5°N 68.0°W
Movement: W at 30 mph
Pressure: 1011 mb

I am faced with a disorganized storm this evening; actually, most likely a sharp tropical wave. While the earlier reconnaissance mission into the tropical cyclone was cut short due to the crew entering Venezuelan airspace, a slew of scatterometer, satellite, and radar fixes strongly suggest that Chantal has lost its closed surface circulation. Another reconnaissance plane is investigating Chantal now, and I imagine they will find an open wave.



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

Most of the deep convection has collapsed, become fragmented, and displaced well to the east of the low-level center. This is likely due to a combination of increasing westerly shear south of a well-defined upper flow off the southern Florida coast, dry air (as seen by arc clouds emanating westward from the cyclone center on satellite), and low-level speed shear. While Chantal has made some comebacks before, a rebound looks less likely this time.

Even if Chantal somehow survives the current hostilities, the 0z GFS and CMC far farther south and take it across the southwestern peninsula of Haiti; the current westward motion in excess of 25 kt may be evidence of a track farther to the south. Haiti is even more mountainous than the Dominican Republic, so that would pretty much be worst case scenario for Chantal. Even if Chantal decides to traverse the less mountainous areas of Hispaniola, a tight circulation with little to no west winds isn't going to last very long. For now, my forecast will maintain some continuity and still take Chantal over the northern portion of Hispaniola, although I have shifted a little to the left in deference to the GFS forecast.

The models show upper-level winds improving over the Bahamas as an upper low develops over the northeastern United States and retrogrades westward, providing a diffluent upper-level environment; however, Chantal will probably not last that long.

In the meantime, the models shear westerly shear increasing even further while the storm traverses Hispaniola, which is not a good sign for Chantal clinging to life.

Chantal remains south of an unseasonably strong mid-level ridge, which is responsible for the rather brisk aclimatological westward motion. Recent satellite fixes would tend to confirm the National Hurricane Center's recent assignment of a more westward component of motion. The global models show the upper low over the Florida Straits moving southward and weakening, which is expected to create a weakness in the western extent of the subtropical ridge and allow Chantal to slow down over the Bahamas. This low is forecast to gradually weaken and ultimately dissipate in a few days, while any residual troughing over the southeastern United States lifts out. With developing mid-level ridging to the north, Chantal is forecast to turn westward near the end of the forecast period, likely into the southeastern United States coast. Once again, this assumes Chantal will survive, but I do not consider this to be particularly likely in light of current trends. The sharp westward turn into the Gulf of Mexico since yesterday is no longer evident, and even if the models do somehow shift west, there will likely be very little left of Chantal to regenerate in an otherwise favorable environment in the Gulf of Mexico. The models are more tightly clustered around a Georgia/South Carolina landfall now, and my forecast will consequently be nudged in that direction as well, showing the center of Chantal just offshore the Georgia coast on Sunday evening.

It should be noted that, even if Chantal loses its status as a tropical cyclone, locally heavy rainfall and strong gusty winds, possibly in exceeding 50 kt, will be possible in squalls across Hispaniola today (Wednesday). The system is likely to also still carry winds to tropical storm force as it traverses eastern Cuba and the Bahamas.

5-day intensity and position

INITIAL 07/10 0600Z 15.5N 68.0W 45 KT 50 MPH
12 hour 07/10 1200Z 17.0N 70.0W 45 KT 50 MPH
24 hour 07/11 0000Z 18.4N 71.8W 45 KT 50 MPH...INLAND OVER HISPANIOLA
36 hour 07/11 1200Z 20.9N 74.6W 40 KT 45 MPH...OVER WATER
48 hour 07/12 0000Z 23.2N 76.5W 40 KT 45 MPH
72 hour 07/13 0000Z 27.3N 78.8W 40 KT 45 MPH
96 hour 07/14 0000Z 29.3N 79.7W 45 KT 50 MPH
120 hour 07/15 0000Z 30.7N 81.4W 45 KT 50 MPH

5-day track forecast



Figure 2. My 5-day forecast track for Chantal.

NHC storm information

000
WTNT33 KNHC 100547
TCPAT3

BULLETIN
TROPICAL STORM CHANTAL INTERMEDIATE ADVISORY NUMBER 9A
NWS NATIONAL HURRICANE CENTER MIAMI FL AL032013
200 AM AST WED JUL 10 2013

...CHANTAL BECOMING DISORGANIZED WHILE IT PASSES TO THE SOUTHWEST OF
PUERTO RICO...


SUMMARY OF 200 AM AST...0600 UTC...INFORMATION
----------------------------------------------
LOCATION...15.5N 68.0W
ABOUT 235 MI...380 KM SSW OF SAN JUAN PUERTO RICO
ABOUT 230 MI...370 KM SSE OF SANTO DOMINGO DOMINICAN REPUBLIC
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 30 MPH...48 KM/H
MINIMUM CENTRAL PRESSURE...1011 MB...29.85 INCHES


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

THE GOVERNMENT OF THE DOMINICAN REPUBLIC HAS DISCONTINUED THE
HURRICANE WATCH FROM BARAHONA TO SAMANA.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* PUERTO RICO
* ENTIRE COAST OF THE DOMINICAN REPUBLIC
* ENTIRE COAST OF HAITI
* TURKS AND CAICOS
* SOUTHEASTERN BAHAMAS

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* U.S. VIRGIN ISLANDS
* VIEQUES AND CULEBRA
* CENTRAL BAHAMAS

INTERESTS IN EASTERN CUBA AND THE NORTHWESTERN BAHAMAS SHOULD
MONITOR THE PROGRESS OF CHANTAL.

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
------------------------------
REPORTS FROM AN AIR FORCE HURRICANE HUNTER AIRCRAFT AND SATELLITE
IMAGES INDICATE THAT CHANTAL IS LOSING ORGANIZATION.

AT 200 AM AST...0600 UTC...THE CENTER OF TROPICAL STORM CHANTAL WAS
ESTIMATED NEAR LATITUDE 15.5 NORTH...LONGITUDE 68.0 WEST. CHANTAL
HAS MOVED RAPIDLY WESTWARD NEAR 30 MPH...48 KM/H OVER THE PAST FEW
HOURS...AND A WEST-NORTHWESTWARD MOTION WITH A GRADUAL DECREASE IN
FORWARD SPEED IS EXPECTED TODAY. A TURN TOWARD THE NORTHWEST IS
EXPECTED BY THURSDAY. ON THE FORECAST TRACK...THE CENTER OF
CHANTAL IS EXPECTED TO BE NEAR OR OVER HISPANIOLA BY THIS
AFTERNOON. CHANTAL IS EXPECTED TO BE NEAR EASTERN CUBA EARLY
THURSDAY AND OVER THE SOUTHEASTERN OR CENTRAL BAHAMAS LATER ON
THURSDAY.

MAXIMUM SUSTAINED WINDS HAVE DECREASED TO NEAR 50 MPH...85
KM/H...WITH HIGHER GUSTS. LITTLE CHANGE IN STRENGTH IS EXPECTED
BEFORE CHANTAL REACHES HISPANIOLA...BUT WEAKENING IS FORECAST AFTER
THAT TIME.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 90 MILES...150 KM...
MAINLY TO THE NORTH OF THE CENTER.

THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 1011 MB...29.85 INCHES.


HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM CONDITIONS COULD OCCUR ACROSS PORTIONS OF
PUERTO RICO DURING THE NEXT SEVERAL HOURS. TROPICAL STORM
CONDITIONS ARE EXPECTED TO REACH THE DOMINICAN REPUBLIC LATER THIS
MORNING. TROPICAL STORM CONDITIONS ARE EXPECTED IN HAITI LATER
TODAY. TROPICAL STORM CONDITIONS ARE POSSIBLE IN THE SOUTHEASTERN
BAHAMAS...THE TURKS AND CAICOS...AND PORTIONS OF THE CENTRAL
BAHAMAS ON THURSDAY.

STORM SURGE...A STORM SURGE...ACCOMPANIED BY DANGEROUS WAVES...WILL
RAISE WATER LEVELS BY AS MUCH AS 1 TO 3 FEET IN THE TROPICAL STORM
WARNING AREA.

RAINFALL...CHANTAL IS EXPECTED TO PRODUCE TOTAL RAIN ACCUMULATIONS
3 TO 6 INCHES OVER PUERTO RICO...THE U.S. VIRGIN ISLANDS...THE
SOUTHEASTERN BAHAMAS...THE DOMINICAN REPUBLIC AND HAITI. ISOLATED
MAXIMUM AMOUNTS OF 10 INCHES ARE POSSIBLE OVER HISPANIOLA.


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

$$
FORECASTER PASCH/BLAKE

2013 Atlantic hurricane season Tropical Storm Chantal

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Tropical weather analysis - July 8, 2013

By: KoritheMan, 3:15 AM GMT on July 09, 2013

Chantal

Tropical Storm Chantal continues to race toward the Windward Islands. As of the most recent NHC advisory, the following information was available on the storm:

Wind: 50 mph, with higher gusts
Location: 12.4°N 56.1°W
Movement: WNW at 26 mph
Pressure: 1010 mb

While the cloud pattern is still a little ragged, convection has increased over the center, and the cyclone appears to still have some banding features. Since there doesn't appear to be any synoptic feature that would induce vertical shear over the tropical cyclone, the current appearance is probably due to lower tropospheric speed shear, which is not surprising considering how quickly Chantal is moving. Earlier microwave data also attested that Chantal is not particularly well-organized, with the low-level center along the western edge of the convective canopy.



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

There is still some dry air in the near-storm environment, which may also be an inhibiting factor to short-term intensification. UW-CIMSS wind shear data and water vapor imagery suggests that some weak mid-level northwesterly flow associated with outflow from a large area of disturbed weather over the southwestern Caribbean Sea and far eastern Pacific may be getting help from the mid-oceanic trough over the Greater Antilles to assist in afflicting dry air into the circulation envelope. Since the large-scale environment is seemingly favorable otherwise, my forecast will continue to assume that Chantal will overcome the short-term hurdles and intensify a little before reaching the Windward Islands late tomorrow morning, but there is considerable uncertainty in this forecast, and I am reminded of the struggles of hurricanes Ernesto and Isaac last year in a similar location with similar conditions. An alternate scenario is for Chantal to lose its closed surface circulation over the next few days due to the fast forward speed, and degenerate into a tropical wave over the eastern or central Caribbean Sea. While most of the models are not showing this, the high is not really forecast to weaken very much in the next three days, so Chantal is not forecast to slow down.

By day three, the global models show an increase in westerly to northwesterly shear as a weak mid- to upper-level trough moves into the eastern United States, which may significantly weaken the system by the time, since it will have already interacted with Hispaniola and eastern Cuba. There are some indications that the long-range upper-level wind pattern over the Bahamas may become a little more favorable for development near the end of the period if Chantal can survive the mountains and shear. The last few cycles of the statistical and dynamical models have showed Chantal turning more to the right while over the Bahamas, but then taking a sharp bend to the left across Florida into the Gulf of Mexico; even the 12z ECMWF takes a weak vorticity center across Florida into the Gulf of Mexico over the weekend into early next week, when the 0z run was previously showing a trajectory into the United States east coast. I still consider the possibility of Chantal getting into the Gulf of Mexico to be fairly low, but if it somehow does, the upper-level wind pattern looks rather favorable, with a westward-moving upper low over the western Gulf Coast providing diffluent flow aloft to any potential cyclone at that time.

Chantal remains well-embedded in an unseasonably strong subtropical ridge and is consequently moving along at a rather quick and unclimatological forward pace, generally toward the west-northwest. There is no large break apparent in the subtropical ridge, and Chantal is forecast to move generally west-northwestward across the Windward Islands tomorrow, then across the eastern and central Caribbean Sea for the rest of Tuesday and into Wednesday evening. A landfall is anticipated along the coast of Hispaniola Wednesday evening, with the cyclone emerging into the Bahamas on Thursday. Beyond that time, the models show a shortwave trough digging into the southeastern United States, which is expected to weaken the ridge over the western Atlantic and cause Chantal to decelerate and turn northwestward. It should be noted that the pattern does not appear very amplified in the models, and the trough is forecast to lift out rather quickly, probably within 24-48 hours, and will likely not allow Chantal to recurve seaward. Things can always change in any given direction, however, and the long-range forecast is highly uncertain.

As mentioned before, there is the potential for a sharp westward bend toward Florida and the Gulf of Mexico beyond the weekend as the trough lifs out. Since the models could just as easily flip back, however, coupled with the fact that we need to see if Chantal survives Hispaniola and Cuba, I chose not to deviate too strongly from my forecast from yesterday. Needless to say, this is a very low-confidence forecast.

If I lived along the southeastern United States or the Gulf Coast, I would be reviewing my hurricane preparedness plans, just in case Chantal makes it.

In the meantime, sustained tropical storm force winds, possibly with gusts to hurricane force, will impact the Windward Islands over the next 24 hours; the sustained wind to gust ratio may be a little higher than normal given the forward speed of Chantal. Heavy rainfall will also be a threat, but the fast forward motion may mitigate the freshwater flood potential.

I still expect Chantal to pass well south of Puerto Rico, but tropical storm force wind gusts, especially in the higher elevations, will still be possible, along with heavy rainfall.

Hispaniola should prepare for the possibility of a near hurricane-strength storm. Fortunately, I do not expect floods of a similar magnitude to more notorious Hispaniola storms like Gustav, Hanna, and Isaac, since Chantal will be moving quickly.

The Bahamas should prepare for tropical storm conditions on Thursday all the way through the weekend, since Chantal is forecast to decelerate -- possibly significantly -- at their latitude.

5-day intensity forecast

INITIAL 07/09 0300Z 12.4N 56.1W 45 KT 50 MPH
12 hour 07/09 1200Z 13.4N 58.9W 50 KT 60 MPH
24 hour 07/10 0000Z 14.6N 62.8W 50 KT 60 MPH
36 hour 07/10 1200Z 16.2N 66.5W 55 KT 65 MPH
48 hour 07/11 0000Z 18.4N 70.5W 55 KT 60 MPH...INLAND OVER HISPANIOLA
72 hour 07/12 0000Z 21.3N 74.5W 40 KT 45 MPH...OVER WATER
96 hour 07/13 0000Z 23.7N 75.3W 40 KT 45 MPH
120 hour 07/14 0000Z 26.1N 77.1W 40 KT 45 MPH

5-day track forecast



Figure 2. My 5-day forecast track for Chantal.

NOTE: I realize there is a difference between the initial position given above, and the initial position on my forecast track graph. This is because I was in the process of disseminating this blog prior to the 0300Z NHC advisory, but my overall forecast philosophy is unchanged.

NHC storm information


000
WTNT33 KNHC 090256
TCPAT3

BULLETIN
TROPICAL STORM CHANTAL ADVISORY NUMBER 5
NWS NATIONAL HURRICANE CENTER MIAMI FL AL032013
1100 PM AST MON JUL 08 2013

...CHANTAL RACING TOWARD THE LESSER ANTILLES...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...12.4N 56.1W
ABOUT 235 MI...380 KM ESE OF BARBADOS
ABOUT 345 MI...555 KM ESE OF ST. LUCIA
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...WNW OR 285 DEGREES AT 26 MPH...43 KM/H
MINIMUM CENTRAL PRESSURE...1010 MB...29.83 INCHES


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

THE GOVERNMENT OF THE DOMINICAN REPUBLIC HAS REPLACED THE TROPICAL
STORM WATCH WITH A TROPICAL STORM WARNING FROM CABO ENGANO TO THE
BORDER WITH HAITI. A TROPICAL STORM WATCH HAS BEEN ISSUED FOR THE
NORTHERN COAST OF HAITI FROM NORTH OF CABO ENGANO TO CABO FRANCES
VIEJO.

A TROPICAL STORM WATCH HAS BEEN ISSUED FOR HAITI.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* BARBADOS
* DOMINICA
* ST. LUCIA
* MARTINIQUE
* GUADELOUPE
* PUERTO RICO
* SOUTHERN COAST OF THE DOMINICAN REPUBLIC FROM CABO ENGANO TO THE
BORDER WITH HAITI

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* ST. VINCENT
* U.S. VIRGIN ISLANDS
* VIEQUES AND CULEBRA
* NORTHERN COAST OF THE DOMINICAN REPUBLIC FROM NORTH OF CABO ENGANO
TO CABO FRANCES VIEJO

INTERESTS IN THE REMAINDER OF THE NORTHERN LEEWARD ISLANDS...THE
SOUTHEASTERN BAHAMAS AND TURKS AND CAICOS SHOULD MONITOR THE
PROGRESS OF CHANTAL.

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

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

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 CHANTAL WAS
LOCATED NEAR LATITUDE 12.4 NORTH...LONGITUDE 56.1 WEST. CHANTAL IS
MOVING TOWARD THE WEST-NORTHWEST NEAR 26 MPH...43 KM/H...AND THIS
GENERAL MOTION IS EXPECTED TO CONTINUE FOR THE NEXT COUPLE OF DAYS.
ON THE FORECAST TRACK...THE CENTER OF CHANTAL WILL MOVE THROUGH THE
LESSER ANTILLES EARLY TUESDAY...MOVE INTO THE EASTERN CARIBBEAN SEA
LATER ON TUESDAY...AND BE NEAR THE DOMINICAN REPUBLIC ON WEDNESDAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 50 MPH...85 KM/H...WITH HIGHER
GUSTS. SOME STRENGTHENING IS FORECAST DURING THE NEXT 48 HOURS.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 90 MILES...
150 KM...MAINLY TO THE NORTH OF THE CENTER.

THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 1010 MB...29.83 INCHES.


HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM CONDITIONS ARE EXPECTED TO REACH PORTIONS OF
THE WINDWARD ISLANDS BY TUESDAY MORNING...AND REACH PUERTO RICO
TUESDAY NIGHT OR EARLY WEDNESDAY. TROPICAL STORM CONDITIONS ARE
EXPECTED TO REACH THE SOUTHEASTERN PORTION OF THE DOMINICAN
REPUBLIC BY WEDNESDAY MORNING. TROPICAL STORM CONDITIONS ARE
POSSIBLE IN HAITI BY LATE WEDNESDAY.

STORM SURGE...A STORM SURGE WILL RAISE WATER LEVELS BY AS MUCH AS 1
TO 3 FEET ABOVE NORMAL TIDE LEVELS IN THE LEEWARD ISLANDS...
WINDWARD ISLANDS...AND PUERTO RICO. A STORM SURGE WILL ALSO RAISE
WATER LEVELS BY AS MUCH AS 2 TO 4 FEET ABOVE NORMAL TIDE LEVELS
ALONG THE SOUTHERN COAST OF THE DOMINICAN REPUBLIC. NEAR THE
COAST...THE SURGE WILL BE ACCOMPANIED BY DANGEROUS WAVES.

RAINFALL...CHANTAL IS EXPECTED TO PRODUCE RAIN ACCUMULATIONS OF
2 TO 4 INCHES OVER THE LEEWARD AND WINDWARD ISLANDS...PUERTO RICO
AND THE U.S. VIRGIN ISLANDS...AND PORTIONS OF THE DOMINICAN
REPUBLIC AND HAITI...WITH MAXIMUM AMOUNTS OF 6 INCHES POSSIBLE.


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

$$
FORECASTER BROWN



Erick

Erick continues to weaken as of the latest NHC advisory:

Wind: 35 mph, with higher gusts
Location: 23.2°N 111.6°W
Movement: NW at 10 mph
Pressure: 1004 mb

Deep convection is quickly disappearing as Erick moves over 23-24C waters. Recent microwave and satellite data suggest that Erick may be staring to turn more to the left. Since the cyclone is already well away from Baja, the government of Mexico has discontinued the tropical storm warning for that peninsula.



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

Erick is forecast to move into even colder water over the next couple of days, possibly falling to below 20C in about 36 hours. It is difficult to see Erick surviving very long in this kind of environment, and the cyclone is forecast to degenerate into a remnant low very soon, and dissipate entirely by 48 hours, if not sooner. My forecast track is a little south of the latest GFS and ECMWF solutions.

5-day intensity forecast

INITIAL 07/09 0300Z 23.2N 111.6W 35 KT 40 MPH
12 hour 07/09 1200Z 23.2N 112.4W 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW
24 hour 07/10 0000Z 23.4M 113.6W 20 KT 25 MPH...POST-TROPICAL/REMNANT LOW
36 hour 07/10 1200Z 23.5N 114.6W 20 KT 25 MPH...POST-TROPICAL/REMNANT LOW
48 hour 07/11 0000Z...DISSIPATED

5-day track forecast



Figure 4. My 5-day forecast track for Erick.

NOTE: I realize there is a difference between the initial position given above, and the initial position on my forecast track graph. This is because I was in the process of disseminating this blog prior to the 0300Z NHC advisory, but my overall forecast philosophy is unchanged.



Future Dorian behind Chantal?

The GFS has indicated the development of tropical cyclone near the Cape Verde Islands for the last several runs. Presumably, this development comes from the vigorous tropical wave getting ready to depart west Africa. The 18z run developed it into a tropical cyclone in about 72 hours. Based on the strength of the Bermuda-Azores ridge, I see potential for another Caribbean cruiser behind Chantal. Given the upper-level wind pattern shown on the GFS, which is strongly anticyclonic, this wave could pose a much bigger threat than Chantal. However, there is considerable uncertainty in both development potential and the future trajectory and strength of this modeled cyclone.

None of the other models show development of this disturbance, but the GFS is probably the best for picking out tropical development.

2013 Atlantic hurricane season 2013 Pacific hurricane season Tropical Storm Chantal Tropical Depression Erick

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Tropical weather analysis - July 8, 2013

By: KoritheMan, 5:29 AM GMT on July 08, 2013

Chantal

The strong tropical wave over the eastern Atlantic has become Tropical Storm Chantal. As of the latest NHC advisory, the following information was issued on the system:

Wind: 40 mph, with higher gusts
Location: 9.8°N 47.2°W
Movement: W at 26 mph
Pressure: 1008 mb

Chantal is a well-organized tropical cyclone, especially considering the aclimatological time of year. A TMI microwave pass at 0156 UTC gave a better estimate of the low-level center, suggesting that it lies very close to the deepest convection, which consists of a tightly-wound band.



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

Chantal is in an environment of low vertical shear and very warm water temperatures. Water vapor imagery suggests the presence of dry air, but the driest airmass is located to the west of Chantal. Since the upper tropospheric flow is primarily easterly, there should not be as much dry air entrainment as would typically be the case in this kind of environment. The models are rather enthusiastic about this system's development chances, with the typically reliable LGEM indicating a peak near 55 kt in 48 hours. Other than the extremely fast forward speed, there do not appear to be any obvious impediments to short-term strengthening, so I will go along with that prediction. It should be noted that there is considerable uncertainty pertaining to Chantal's intensity at longer ranges, particularly beyond 72 hours when the models suggest an increase in shear. The likelihood of land interaction with Hispaniola and Cuba further complicates the forecast.

If the current rate of organization persists, Chantal could become a hurricane within the next 48 hours. Although unlikely, I would give Chantal a 10% chance of reaching hurricane strength prior to reaching the Windward Islands. Interests in those islands should be very cognizant of Chantal's progress over the next 48 hours, as they will be the first to feel the effects of the storm.

Chantal is well-embedded within a strong, nearly uniform easterly steering regime to the south of an abnormally strong subtropical ridge. A well-defined upper low north of Puerto Rico is forecast to move westward and weaken over the next few days, becoming highly diffuse after about 72 hours. Normally this would favor a more westward track at longer ranges, toward the Gulf of Mexico, but the models show another shortwave trough moving into the southeastern United States at that time, which is likely to reinforce the weakness of the ridge and prevent Chantal from making too much additional westward progress. Another thing arguing against Chantal making it into the Gulf even if she somehow defied all odds is the presence of an upper low forecast to detach from the aforementioned shortwave trough and move westward toward the western Gulf Coastal region beyond day five.

While there are some notable differences amongst the guidance at longer ranges, they all indicate a threat to the southeastern United States coast. It is way too early to speculate as to where or if Chantal will make US landfall, and our buddies in the Caribbean will have to deal with her first, starting with the Windward Islands, then Puerto Rico, then Hispaniola, and finally Cuba.

Tropical storm force winds are likely to impact a large swath of the Caribbean islands as Chantal moves west-northwest across that region; this includes Puerto Rico, even though they should be well north of the forecast track. Heavy rains capable of causing flooding will also affect those areas. Chantal is anticipated to impact the Bahamas as well, but it is too early to delineate impacts to that area, since we need to see how Chantal fares after tussling with the Greater Antilles.

Some deceleration is expected at days four and five as the subtropical ridge over the western Atlantic weakens with the approach of the modeled shortwave trough. The pattern does not look amplified enough in the models at this time for Chantal to recurve out to sea, but things can always change.

Tropical storm warnings are in effect for Barbados, Dominica, and Saint Lucia, while a tropical storm watch is in effect for Saint Vincent.

5-day intensity forecast

INITIAL 07/08 0300Z 35 KT 40 MPH
12 hour 07/08 1200Z 40 KT 45 MPH
24 hour 07/09 0000Z 45 KT 50 MPH
36 hour 07/09 1200Z 50 KT 60 MPH...APPROACHING WINDWARD ISLANDS
48 hour 07/10 0000Z 55 KT 65 MPH
72 hour 07/11 0000Z 50 KT 60 MPH...INLAND OVER SOUTHWESTERN HAITI
96 hour 07/12 0000Z 40 KT 45 MPH
120 hour 07/13 0000Z 40 KT 45 MPH

5-day track forecast



Figure 2. My 5-day forecast track for Chantal.

NHC storm information

000
WTNT33 KNHC 080301
TCPAT3

BULLETIN
TROPICAL STORM CHANTAL ADVISORY NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL AL032013
1100 PM EDT SUN JUL 07 2013

...TROPICAL STORM CHANTAL FORMS OVER THE CENTRAL TROPICAL
ATLANTIC...
...RACING WEST-NORTHWESTWARD TOWARD THE LESSER ANTILLES...


SUMMARY OF 1100 PM EDT...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...9.8N 47.2W
ABOUT 865 MI...1390 KM ESE OF BARBADOS
MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/H
PRESENT MOVEMENT...W OR 275 DEGREES AT 26 MPH...43 KM/H
MINIMUM CENTRAL PRESSURE...1008 MB...29.77 INCHES


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

THE GOVERNMENT OF BARBADOS HAS ISSUED A TROPICAL STORM WARNING FOR
BARBADOS AND DOMINICA AND A TROPICAL STORM WATCH FOR ST. VINCENT.

THE GOVERNMENT OF SAINT LUCIA HAS ISSUED A TROPICAL STORM WARNING
FOR SAINT LUCIA.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

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

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* SAINT VINCENT

A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA...IN THIS CASE WITHIN 24
TO 36 HOURS.

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

ADDITIONAL WATCHES OR WARNINGS MAY BE REQUIRED FOR PORTIONS OF THE
LESSER ANTILLES ON MONDAY MORNING.

INTERESTS IN THE EASTERN CARIBBEAN SHOULD MONITOR THE PROGRESS OF
CHANTAL.

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


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 1100 PM EDT...0300 UTC...THE CENTER OF TROPICAL STORM CHANTAL WAS
LOCATED NEAR LATITUDE 9.8 NORTH...LONGITUDE 47.2 WEST. CHANTAL IS
MOVING TOWARD THE WEST NEAR 26 MPH...43 KM/H...AND THIS SAME RAPID
WESTWARD OR WEST-NORTHWESTWARD MOTION IS EXPECTED DURING THE NEXT
COUPLE OF DAYS. ON THE FORECAST TRACK...THE CENTER OF CHANTAL SHOULD
APPROACH THE LESSER ANTILLES LATE MONDAY NIGHT OR EARLY TUESDAY...
AND MOVE INTO THE EASTERN CARIBBEAN SEA ON TUESDAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 40 MPH...65 KM/H...WITH HIGHER
GUSTS. SOME STRENGTHENING IS FORECAST DURING THE NEXT 48 HOURS.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 60 MILES...95 KM
FROM THE CENTER.

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


HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM CONDITIONS ARE EXPECTED WITHIN THE WARNING
AREA MONDAY NIGHT AND EARLY TUESDAY. TROPICAL STORM CONDITIONS ARE
POSSIBLE IN THE WATCH AREA EARLY ON TUESDAY.

RAINFALL...CHANTAL IS EXPECTED TO PRODUCE RAIN ACCUMULATIONS OF 2 TO
4 INCHES OVER THE LEEWARD AND WINDWARD ISLANDS...WITH MAXIMUM
AMOUNTS OF 6 INCHES POSSIBLE.


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

$$
FORECASTER KIMBERLAIN/BROWN



Erick

Tropical Storm Erick continues to weaken:

Wind: 60 mph, with higher gusts
Location: 20.8°N 108.7°W
Movement: WNW at 9 mph
Pressure: 996 mb

There is still some deep convection, but is confined to the northern portion of the circulation, which appears to be over warmer waters. Although the deep convection is weakening, there is still some rather prominent banding to the north of the center, so Erick will not immediately weaken.



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

Erick does not have long to live, the current convection notwithstanding. The cyclone is forecast to cross the 26C isotherm shortly, with water temperatures cooling rapidly in about 24 hours, to as low as 20C beyond that point. Thus, dissipation is forecast in about 48 hours in agreement with the intensity guidance, although it could occur about 12 hours sooner given the extremely cold water along the forecast track. The global models show the residual circulation completely dissipating after 72 hours, so post-tropical Erick is forecast to lose its identity by that time.

Erick remains south of a well-established low- to mid-level ridge, which is allowing the tropical storm to move toward the west-northwest. Although a tropical storm warning remains in effect for Baja California Del Sur, the guidance suggests that the cyclone will remain well south of that peninsula. Given the pattern I don't see any reason to disagree with this, so my forecast will continue to show Erick passing offshore. While I would currently not anticipate tropical storm force winds to affect the southern Baja Peninsula, it always pays to play it safe, and interests in the warning area should continue monitoring the progress of Erick over the next 24 hours. Increased surf and locally heavy rainfall are likely to occur there regardless of how far Erick passes offshore.

5-day intensity forecast

INITIAL 07/08 0300Z 50 KT 60 MPH
12 hour 07/08 1200Z 45 KT 50 MPH
24 hour 07/09 0000Z 35 KT 40 MPH
36 hour 07/09 1200Z 30 KT 35 MPH
48 hour 07/10 0000Z 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW
72 hour 07/11 0000Z 20 KT 25 MPH...POST-TROPICAL/REMNANT LOW
96 hour 07/12 0000Z...DISSIPATED

5-day track forecast



Figure 4. My 5-day forecast track for Erick.

NHC storm information

000
WTPZ35 KNHC 080248
TCPEP5

BULLETIN
TROPICAL STORM ERICK ADVISORY NUMBER 15
NWS NATIONAL HURRICANE CENTER MIAMI FL EP052013
800 PM PDT SUN JUL 07 2013

...ERICK TO PASS NEAR THE SOUTHERN TIP OF THE BAJA
PENINSULA MONDAY MORNING...


SUMMARY OF 800 PM PDT...0300 UTC...INFORMATION
----------------------------------------------
LOCATION...20.8N 108.7W
ABOUT 165 MI...265 KM SSE OF THE SOUTHERN TIP OF BAJA CALIFORNIA
MAXIMUM SUSTAINED WINDS...60 MPH...95 KM/H
PRESENT MOVEMENT...WNW OR 300 DEGREES AT 9 MPH...15 KM/H
MINIMUM CENTRAL PRESSURE...996 MB...29.41 INCHES


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

NONE.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* BAJA CALIFORNIA SUR FROM SANTA FE TO LA PAZ

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


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 800 PM PDT...0300 UTC...THE CENTER OF TROPICAL STORM ERICK WAS
LOCATED NEAR LATITUDE 20.8 NORTH...LONGITUDE 108.7 WEST. ERICK IS
MOVING TOWARD THE WEST-NORTHWEST NEAR 9 MPH...15 KM/H. A WEST-
NORTHWESTWARD TO NORTHWESTWARD MOTION IS EXPECTED OVER THE NEXT
COUPLE OF DAYS. ON THE FORECAST TRACK...THE CENTER OF ERICK
SHOULD PASS NEAR OR JUST SOUTH OF THE SOUTHERN TIP OF THE BAJA
CALIFORNIA PENINSULA MONDAY MORNING.

MAXIMUM SUSTAINED WINDS ARE NEAR 60 MPH...95 KM/H...WITH HIGHER
GUSTS. GRADUAL WEAKENING IS FORECAST DURING THE NEXT 48 HOURS.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 70 MILES...110 KM
FROM THE CENTER.

THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 996 MB...29.41 INCHES.


HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM CONDITIONS ARE EXPECTED TO BEGIN WITHIN
THE WARNING AREA IN BAJA CALIFORNIA SUR EARLY MONDAY.

RAINFALL...ERICK IS EXPECTED TO PRODUCE TOTAL RAIN ACCUMULATIONS OF
1 TO 2 INCHES OVER WESTERN JALISCO...NAYARIT...SOUTHERN SINALOA...
AND THE SOUTHERN BAJA CALIFORNIA PENINSULA.

SURF...SWELLS GENERATED BY ERICK ARE AFFECTING PORTIONS OF THE
COAST OF SOUTHWESTERN MEXICO AND THE SOUTHERN PART OF THE BAJA
CALIFORNIA. THESE SWELLS ARE LIKELY TO CAUSE LIFE-THREATENING
SURF AND RIP CURRENT CONDITIONS.


NEXT ADVISORY
-------------
NEXT INTERMEDIATE ADVISORY...1100 PM PDT.
NEXT COMPLETE ADVISORY...200 AM PDT.

$$
FORECASTER BROWN

Tropical Storm Chantal Tropical Storm Erick 2013 Atlantic hurricane season 2013 Pacific hurricane season

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Tropical weather analysis - July 7, 2013

By: KoritheMan, 6:18 AM GMT on July 07, 2013

Erick

Erick became the fourth hurricane of the 2013 Pacific hurricane season Saturday afternoon. As of the just released intermediate advisory from the NHC, the following information was posted on the hurricane:

Wind: 80 mph, with higher gusts
Location: 18.9°N 106.1°W
Movement: NW at 9 mph
Pressure: 984 mb
Category: 1 (Saffir-Simpson Hurricane Wind Scale)

After sputtering a bit near 0z, Erick has made a bit of a comeback this morning. The prominent curved band to the west has wrapped into the center and has assisted in reigniting the central convection, which consists of a well-defined central dense overcast with very cold cloud top temperatures. The 6z satellite classification from SAB still supported hurricane strength.



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

Since there doesn't appear to be a lot of shear affecting Erick and the waters are still warm, the primary reason for the convective hiccup earlier was likely the circulation interacting with the rather mountainous terrain of southwestern Mexico. While the upper tropospheric shear is forecast to get even weaker over the next several days, the hurricane is forecast to move over some rather cold waters, which cool to as low as 20C in about 60 hours. This is forecast to bring about an abrupt demise of the tropical cyclone, and Erick is forecast to lose its status a tropical cyclone in about 72 hours, but I have seen eastern Pacific tropical cyclones weaken rather quickly in my years of forecasting, and it would certainly be of no surprise if Erick decided to give up on life sooner.

Following the typical nighttime progression, it's been a little difficult to determine Erick's initial motion, but it appears to still be moving northwest and seems to have slowed down some, which would coincide well with the NHC 11:00 PM PDT intermediate advisory. The short-term forecast track of Erick is riddled with uncertainty; the 12z ECMWF showed the center moving inland over southern Baja California, while the GFS continues to indicate a trajectory that is just offshore. Water vapor imagery suggests that there is a small upper-level trough across southern California that appears to be moving eastward, which might be attempting to weaken the ridge to the north of Erick a little; this could explain the recent deceleration of the storm. On the other hand, satellite fixes over the last few hours do not suggest that Erick has moved much closer to the Mexican coast, but this is always riddled with an enormous degree of uncertainty when I'm forced to rely on nighttime satellite imagery. The few microwave passes we did get over the last few hours haven't been of much help in locating the center or determining the cyclone's forward motion, because the passes only captured a portion of the circulation.

Because of the continued uncertainty, interests along the southwestern coast of Mexico and the southern Baja Peninsula should carefully follow the progress of Erick over the next couple of days. A hurricane watch remains in effect from Manzanillo to Cabo Corrientes, while a tropical storm warning remains posted for the southern Baja Peninsula from Santa Fe to La Paz; a tropical storm warning is also in effect for the southwest coast of the mainland from Punta San Telmo to Cabo Corrientes.

Regardless of whether the core of the cyclone remains offshore or passes over the coast, Erick is expected to deliver sustained tropical storm force winds, heavy rains, flooding, and increased storm surge along the coast in the warning area, including Baja California Del Sur. Interests in those areas should take the necessary preparedness precautions.


5-day intensity forecast

INITIAL 07/07 0400Z 70 KT 80 MPH
12 hour 07/07 1200Z 70 KT 80 MPH
24 hour 07/08 0000Z 65 KT 75 MPH
36 hour 07/08 1200Z 50 KT 60 MPH
48 hour 07/09 0000Z 40 KT 45 MPH
72 hour 07/10 0000Z 30 KT 35 MPH...POST-TROPICAL/REMNANT LOW
96 hour 07/11 0000Z 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW
120 hour 07/12 0000Z...DISSIPATED



5-day track forecast



Figure 2. My 5-day forecast track for Erick.

NHC storm information

000
WTPZ35 KNHC 070536
TCPEP5

BULLETIN
HURRICANE ERICK INTERMEDIATE ADVISORY NUMBER 11A
NWS NATIONAL HURRICANE CENTER MIAMI FL EP052013
1100 PM PDT SAT JUL 06 2013

...CENTER OF ERICK CONTINUES TO MOVE PARALLEL TO THE SOUTHWESTERN
COAST OF MEXICO...


SUMMARY OF 1100 PM PDT...0600 UTC...INFORMATION
-----------------------------------------------
LOCATION...18.9N 106.1W
ABOUT 120 MI...190 KM W OF MANZANILLO MEXICO
ABOUT 370 MI...595 KM SE OF THE SOUTHERN TIP OF BAJA CALIFORNIA
MAXIMUM SUSTAINED WINDS...80 MPH...130 KM/H
PRESENT MOVEMENT...NW OR 310 DEGREES AT 9 MPH...15 KM/H
MINIMUM CENTRAL PRESSURE...984 MB...29.06 INCHES


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

NONE.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A HURRICANE WATCH IS IN EFFECT FOR...
* MANZANILLO TO CABO CORRIENTES

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* PUNTA SAN TELMO TO CABO CORRIENTES
* BAJA CALIFORNIA SUR FROM SANTA FE TO LA PAZ

A HURRICANE WATCH MEANS THAT HURRICANE CONDITIONS ARE POSSIBLE
WITHIN THE WATCH AREA.

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

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


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 1100 PM PDT...0600 UTC...THE CENTER OF HURRICANE ERICK WAS
LOCATED NEAR LATITUDE 18.9 NORTH...LONGITUDE 106.1 WEST. ERICK IS
MOVING TOWARD THE NORTHWEST NEAR 9 MPH...15 KM/H. A GENERAL
NORTHWEST TO WEST-NORTHWEST MOTION IS EXPECTED OVER THE NEXT COUPLE
OF DAYS. ON THE FORECAST TRACK...THE CORE OF ERICK SHOULD MOVE
PARALLEL TO...BUT REMAIN OFFSHORE OF...THE COAST OF SOUTHWESTERN
MEXICO SUNDAY MORNING. HOWEVER...ANY DEVIATION TO THE RIGHT OF THE
FORECAST TRACK COULD BRING THE CENTER NEAR OR OVER THE PACIFIC
COAST OF MEXICO. ERICK IS FORECAST TO APPROACH THE SOUTHERN BAJA
CALIFORNIA PENINSULA LATE SUNDAY AND PASS NEAR THE SOUTHERN PORTION
OF THE PENINSULA SUNDAY NIGHT OR EARLY MONDAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 80 MPH...130 KM/H...WITH HIGHER
GUSTS. LITTLE CHANGE IN STRENGTH IS FORECAST THROUGH SUNDAY
MORNING. GRADUAL WEAKENING IS FORECAST TO BEGIN LATER ON SUNDAY.

HURRICANE FORCE WINDS EXTEND OUTWARD UP TO 25 MILES...35 KM...FROM
THE CENTER...AND TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 80
MILES...130 KM.

THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 984 MB...29.06 INCHES.


HAZARDS AFFECTING LAND
----------------------
WIND...HURRICANE CONDITIONS ARE POSSIBLE IN THE HURRICANE WATCH AREA
EARLY SUNDAY. TROPICAL STORM CONDITIONS ARE LIKELY OCCURRING OVER
THE MAINLAND MEXICAN COAST IN PORTIONS OF THE WARNING AREA...AND
SHOULD CONTINUE THROUGH SUNDAY MORNING. TROPICAL STORM CONDITIONS
ARE EXPECTED TO BEGIN WITHIN THE WARNING AREA IN BAJA CALIFORNIA
SUR BY LATE SUNDAY NIGHT OR EARLY MONDAY.

RAINFALL...ERICK IS EXPECTED TO PRODUCE TOTAL RAIN ACCUMULATIONS OF
3 TO 5 INCHES OVER WESTERN GUERRERO...MICHOACAN...COLIMA...
JALISCO...AND SOUTHERN NAYARIT MEXICO...WITH POSSIBLE ISOLATED
MAXIMUM AMOUNTS OF 8 INCHES. THESE RAINS COULD CAUSE LIFE-
THREATENING FLASH FLOODS AND MUD SLIDES.

SURF...SWELLS GENERATED BY ERICK ARE AFFECTING THE COAST OF
SOUTHWEST MEXICO. THESE SWELLS ARE LIKELY TO CAUSE LIFE-
THREATENING SURF AND RIP CURRENT CONDITIONS.


NEXT ADVISORY
-------------
NEXT COMPLETE ADVISORY...200 AM PDT.

$$
FORECASTER PASCH



Invest 94L

A large area of cloudiness and showers over the western and central Gulf of Mexico shows no signs of organization. I don't have too much to say about this system, and it actually looked more organized 24 hours ago. There appears to be several embedded swirls comprising a larger-scale cyclonic gyre; I see a center off the coast of Mexico near where the original coordinates of 94L were, and one south of the central coast of Louisiana, but scatterometer and buoy data suggest that any such circulations are confined to the middle troposphere.

While the shear has actually decreased to about 20 kt and turned to a more northerly direction behind the upper low and trailing trough moving through Louisiana, the models indicate that the light northerly flow will soon give way to moderate to strong northerly flow, which will curb any development potential for a northward-moving system.

With a ridge continuing to build over Texas and northern Mexico, the only trajectory for this broad disturbance is north, toward the coasts of Texas or Louisiana, depending on where the center -- if there is one -- decides to consolidate.

Although development is not expected, heavy rains are expected across a large portion of the northwestern and northern Gulf Coasts; however, the slew of flash flood watches that were in effect over the last couple of days for these areas have been almost entirely dropped, and based on current convective trends, it does not appear that this will be a flood of Biblical proportions, just some locally heavy showers with embedded patches of local flooding.

The offshore marine data does not show any evidence of strong winds, so coastal flooding should not be a big factor like previously thought.

Probability of development in 48 hours: 0%



Invest 95L

A vigorous tropical wave in the eastern Atlantic located about 1500 miles east-southeast of the Windward Islands is showing signs of organization. Satellite images suggest a large and well-defined curved band is evident to the west of the low-level center, and I also see the first signs of anticyclonic outflow with this system, along the western side.



Figure 3. Latest infrared satellite image of Invest 95L. Image credit: NOAA's Satellite Services Division (SSD).

Although this wave is fairly well-organized, especially considering the latitude, there are no indications from satellite or scatterometer passes over the last 12 hours that this low has acquired a closed surface circulation; this is difficult to accomplish with systems that are still locked within the confines of the ITCZ.

While this system is moving rather quickly toward the west -- at about 25 mph -- the global models suggest that the ridge will weaken a little over the next few days, allowing a more west-northwestward motion to ensue at that time. The wave is forecast to move through the southern Windward Islands late Tuesday spreading heavy rains and gusty winds, possibly to tropical storm force.

It should be noted that, while environmental conditions are forecast to remain conducive for development during the next couple of days, the global models show a sharp increase in westerly shear in about 72 hours, or right around the time the wave reaches the Windward Island archipelago. With the wave moving west and the shear coming from that direction as well, I can't see 95L surviving very long in the eastern Caribbean Sea. If in fact the system becomes a tropical cyclone prior to that point, which is a possibility, it may be able to generate enough of an anticyclone aloft to successfully shield itself from the forthcoming vertical wind shear, and survive as at least a weak tropical cyclone in the eastern Caribbean. There are far too many variables right now to say with any confidence whether or not this system will develop, or where it will go. I favor a general WNW track once the system gets near the Windward Islands, but once it reaches the longitude of Haiti, I do not know if it will continue toward the Bahamas and the southeastern United States, or if it will continue westward into Central America, or whether it will move into the Gulf of Mexico. Based on the low latitude of the disturbance and the strength of the Bermuda-Azores ridge in the models, I do not currently see this system recurving out to sea.

Once again, to have a tropical wave this convectively active this early in the year does not bode particularly well for the rest of the season, and it is likely to be a very active one.

Probability of development in 48 hours: 40%

2013 Pacific hurricane season 2013 Atlantic hurricane season Hurricane Erick Invest 94L Invest 95L

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Tropical weather analysis - July 6, 2013

By: KoritheMan, 5:57 AM GMT on July 06, 2013

Erick

Erick continues to strengthen, and is just under hurricane strength according to the latest NHC advisory:

Wind: 70 mph, with higher gusts
Location: 17.0°N 103.8°W
Movement: NW at 10 mph
Pressure: 991 mb

Erick is sporting a satellite signature that is typical of tropical storms on the verge of intensifying to hurricanes; the deep convection has taken on tightly-wound banding, and conventional satellite fixes throughout the last 12 hours have showed hints of a developing eye. A timely 0230 UTC SSMI pass showed a well-defined ring of convection surrounding a primitive eye feature; incidentally, the pass also showed that the mid-level eye feature was displaced a little northwest of the low-level one, which likely signals that there is still a little bit of southeasterly shear over Erick.



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

Environmental conditions appear supportive of continued intensification, with very warm sea surface temperatures and low to moderate vertical wind shear. Most of the guidance makes Erick a hurricane over the next 24 hours, with the 0z intensity consensus currently suggesting a peak near 70 kt. I will go along with this. Beyond 24 hours, the cyclone will be approaching cooler water; waters which rapidly cool subsequent to that time. Thus, my forecast shows Erick weakening rather quickly after 36 hours, and the tropical cyclone is expected to lose that nominal status in about 96 hours, although it could occur a little sooner, particularly if Erick moves north of the forecast track.

While satellite and microwave fixes suggest that Erick continues moving northwest gravitating toward a residual weakness in the mid-level ridge to the north, water vapor imagery suggests that the mid-level flow is beginning to amplify as a slow-moving mid-level trough departs the Texas coastal region. This is causing the ridge to rebuild to the north of the tropical cyclone, which seems to be occurring a little faster than indicated by the majority of the guidance; this leads me to the conclusion that Erick will turn westward quicker than indicated by the guidance or the NHC. My forecast track is generally along the southern edge of the model consensus, especially beyond day two, and is quite a bit south of the 0300 UTC National Hurricane Center forecast.

Regardless, there is a wide enough margin for error that Erick could still reasonably make landfall along the southwestern coast of Mexico, and it is possible a hurricane watch will be issued later this morning. Interests in the tropical storm warning area should take the necessary precautions to prepare for Erick's potential arrival.

Even if Erick does not make landfall, it is expected to produce tropical storm force winds (especially gusts) in squalls, along with very heavy rainfall capable of causing flash flooding and mudslides, which will be capable of causing loss of life. Treacherous sea conditions in the form of strong rip currents, locally high storm surge, and large battering waves will also accompany Erick as it parallels the coast.

5-day intensity forecast

INITIAL 07/06 0500Z 60 KT 70 MPH
12 hour 07/06 1200Z 65 KT 75 MPH
24 hour 07/07 0000Z 70 KT 80 MPH
36 hour 07/07 1200Z 65 KT 70 MPH
48 hour 07/08 0000Z 55 KT 65 MPH
72 hour 07/09 0000Z 30 KT 35 MPH
96 hour 07/10 0000Z 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW
120 hour 07/11 0000Z...DISSIPATED

5-day track forecast



Figure 2. My 5-day forecast track for Erick.



NHC storm information

000
WTPZ35 KNHC 060538
TCPEP5

BULLETIN
TROPICAL STORM ERICK INTERMEDIATE ADVISORY NUMBER 7A
NWS NATIONAL HURRICANE CENTER MIAMI FL EP052013
1100 PM PDT FRI JUL 05 2013

...ERICK STILL JUST BELOW HURRICANE STRENGTH...


SUMMARY OF 1100 PM PDT...0600 UTC...INFORMATION
-----------------------------------------------
LOCATION...17.0N 103.8W
ABOUT 155 MI...250 KM SSE OF MANZANILLO MEXICO
ABOUT 565 MI...910 KM SE OF THE SOUTHERN TIP OF BAJA CALIFORNIA
MAXIMUM SUSTAINED WINDS...70 MPH...110 KM/H
PRESENT MOVEMENT...NW OR 315 DEGREES AT 9 MPH...14 KM/H
MINIMUM CENTRAL PRESSURE...991 MB...29.26 INCHES


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

NONE.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* ZIHUATANEJO TO CABO CORRIENTES

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

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 1100 PM PDT...0600 UTC...THE CENTER OF TROPICAL STORM ERICK WAS
LOCATED NEAR LATITUDE 17.0 NORTH...LONGITUDE 103.8 WEST. ERICK IS
MOVING TOWARD THE NORTHWEST NEAR 9 MPH...14 KM/H. A GENERAL
NORTHWEST TO WEST-NORTHWEST MOTION IS EXPECTED OVER THE NEXT COUPLE
OF DAYS. ON THE FORECAST TRACK...THE CORE OF ERICK SHOULD MOVE
PARALLEL TO...BUT REMAIN OFFSHORE OF...THE COAST OF SOUTHWESTERN
MEXICO.

MAXIMUM SUSTAINED WINDS ARE NEAR 70 MPH...110 KM/H...WITH HIGHER
GUSTS. ERICK IS FORECAST TO BECOME A HURRICANE AT ANY TIME.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 105 MILES...165 KM
FROM THE CENTER PRIMARILY IN THE NORTHEAST QUADRANT.

THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 991 MB...29.26 INCHES.


HAZARDS AFFECTING LAND
----------------------
RAINFALL...ERICK IS EXPECTED TO PRODUCE TOTAL RAIN ACCUMULATIONS
OF 3 TO 5 INCHES OVER SOUTHWESTERN OAXACA...SOUTHERN GUERRERO...
SOUTHERN MICHOACAN...COLIMA...AND SOUTHERN JALISCO MEXICO...WITH
POSSIBLE ISOLATED MAXIMUM AMOUNTS OF 8 INCHES. THESE RAINS COULD
CAUSE LIFE-THREATENING FLASH FLOODS AND MUD SLIDES.

WIND...TROPICAL STORM CONDITIONS ARE LIKELY TO SPREAD WESTWARD
ACROSS THE WARNING AREA TONIGHT AND SATURDAY.


NEXT ADVISORY
-------------
NEXT COMPLETE ADVISORY...200 AM PDT.

$$
FORECASTER BEVEN



Invest 94L

A large area of showers and thunderstorms over the western and central Gulf of Mexico is associated with a surface trough interacting with an upper-level trough along the northern Gulf Coast. Looking agonizingly tonight for evidence of any sort of circulation pattern, I'm just not seeing it. Shortwave infrared satellite images indicate that there could be a mid-level circulation near 25.5N 90.5W, but this was not supported at all by CIMSS 500 mb vorticity data over the last six hours. In addition, there has not been a center fix or any model runs on what's actually supposed to be 94L -- in the southwestern Gulf -- since 18z Friday (2:00 PM). Looking at that area now, there is literally no evidence of even a faint mid-level rotation, and I expect that any surface center which did form in the southwestern Gulf has long since dissipated.

There is still about 30 kt of westerly shear over the disturbance associated with the south side of the upper-level trough moving through Louisiana, but the tendency has been for the shear to slowly decrease over the last 24 hours. The global models continue to indicate that the upper tropospheric flow could relax considerably over the next 24-48 hours, but how much the system can take advantage of this forecast depends largely on how fast a surface circulation can develop underneath the convection south of the Louisiana coast, and also how long the system remains over water; if a center reformation is indeed occurring in the aforementioned convective mass, there could be fits and wobbles in the track over the day on Saturday as the low-level center attempts to get tucked underneath the convection and avoid the shear. If that were to happen, the system could have a little more time over water than currently forecast.

In any event, I do not think the system has either the time nor the patience to become a tropical cyclone before moving ashore the northern Gulf Coast in the next 24-36 hours, but it will spread heavy rains capable of causing flooding in short bursts; flash flood watches are already in effect for a large portion of the northern Gulf Coast in anticipation of this threat. Strong gusty winds, particularly along the coast, will also be a factor, which could produce some coastal flooding, especially if the low decides to meander.

Upper air data over the Gulf Coast region shows that winds are backing over Texas and western Louisiana, suggesting that a low- to mid-level ridge is attempting to rebuild in the wake of the trough moving through Louisiana; this would tend to discourage any significant westward component of motion from the disturbance. Since the trough appears to be moving through Louisiana, albeit slowly, I would expect that any system which develops amidst the convection south of the Louisiana coast would move generally northward, with a possible turn to the northeast after landfall occurs along the southeastern Louisiana coast. I'm favoring a landfall near Grand Isle at the moment, but it could come in a little farther east if the trough begins to move a little quicker.

Surface pressures are not falling, and any development is expected to be slow.

Probability of development in 48 hours: 20%



Eastern Atlantic tropical wave

Another vigorous tropical wave unseasonable for the month of July is located in the far eastern Atlantic about 700 miles southwest of the Cape Verde Islands. Scatterometer data earlier on Friday suggested a broad surface circulation that was elongated from west-northwest to east-southeast. This system and its associated surface low are still trapped in the ITCZ, and development cannot occur in that situation. The system is also rather far to the south, at about 7N, which also argues against significant development since low pressure centers that far south can't successfully leverage the Earth's spin.

Interestingly, there's not a lot of shear over the disturbance, and the models keep it fairly light over the next several days. This wave is expected to move westward to west-northwestward.

Probability of development in 48 hours: 10%

2013 Pacific hurricane season Tropical Storm Erick Invest 94L

Updated: 6:10 AM GMT on July 06, 2013

Permalink

Tropical weather analysis - July 5, 2013

By: KoritheMan, 6:02 AM GMT on July 05, 2013

Dalila

Dalila continues to weaken as of the latest NHC advisory:

Wind: 35 mph, with higher gusts
Location: 17.3°N 111.0°W
Movement: W at 7 mph
Pressure: 1006 mb

I'm afraid I can't say much more about Dalila. The cyclone is basically a swirl of low-level clouds with the occasional appearance of transient convection that quickly gets sheared away by strong upper-level winds. There is an ongoing burst of deep convection now, but I expect it will be sheared away before long.



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

The shear is forecast to continue, and based upon water vapor imagery showing high cirrus clouds blowing into the cyclone from the southeast, I feel that the global models may actually be underestimating the shear vector. With that in mind, Dalila is forecast to decay into a remnant low in about 24 hours, but it would surprise me if it occurred sooner.

There isn't much to say about the track, either. Dalila is moving generally westward to the south of a mid-level ridge. The global models suggest the possibility that Dalila could interact with newly-formed Tropical Storm Erick, located several hundred miles to the east. This is a good possibility given that Erick has gotten stronger in a hurry. Because of that possibility, I will show Dalila slowing down considerably over the remainder of its life.

5-day intensity forecast

INITIAL 07/05 0300Z 30 KT 35 MPH
12 hour 07/05 1200Z 30 KT 35 MPH
24 hour 07/06 0000Z 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW
36 hour 07/06 1200Z 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW
48 hour 07/07 0000Z 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW
72 hour 07/08 0000Z...DISSIPATED

5-day track forecast



Figure 2.. My 5-day forecast track for Dalila.


Erick

Tropical Storm Erick, the fifth named storm of the season, formed late Thursday from what was previously Invest 97E. As of the most recent NHC bulletin, the following information was available on the storm:

Wind: 45 mph, with higher gusts
Location: 14.9°N 100.7°W
Movement: NW at 12 mph
Pressure: 1004 mb

The satellite presentation is rather impressive, with a large and prominent central dense overcast; in fact, Erick has been generating convective cloud tops upwards of -90C at times. There a couple of curved bands trying to form to the north and east, which may signal that Erick is starting to strengthen.



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

Although Erick is triggering some rather intense thunderstorms, water vapor imagery suggests that the upper-level outflow of the cyclone is limited to the southeast, implying that the tropical storm continues to experience southeasterly to easterly shear. Environmental conditions are expected to remain at least marginally conducive, however, and the shear will probably not be enough to prevent Erick from strengthening. Beyond day three, the cyclone is forecast to cross the 26C isotherm and move into much colder waters; at that point, weakening is anticipated, and Erick could become a remnant low even sooner than indicated below. Based on current organization trends, my intensity forecast is a little above the latest intensity consensus.

Locating the center of Erick has been a rather exhausting task this evening. A couple of microwave passes between 0 and 2z suggested that the cyclone center was located along the far northeastern edge of the convective cloud shield. However, recent satellite fixes strongly suggest -- to me -- that the cyclone center is located a little farther south than those fixes would suggest, and closer to the deepest convection. If I'm correct, this will keep Erick farther offshore the coast of Mexico; but with all the tricks infrared imagery can play on a mind, I could just as easily be mistaken.

Erick appears to be moving generally northwestward, although it may have turned left a little bit over the last couple hours, possibly due to the center following the convection. The models are split, with some of the bringing Erick dangerously close to -- or into -- the southwest coast of Mexico, and others keeping it offshore. There are also some timing differences on when Erick will turn to the west-northwest, but in general, the guidance suggests this will occur in about 48 hours. My forecast is a little south of the current National Hurricane Center one in the short-term due to my personal musings of the center being farther south than officially estimated, but gradually blends in after that. Due to the model spread, it is difficult to tell how close Erick will come to the coast, so interests along the coast of Mexico should monitor the progress of Erick. Tropical storm watches and warnings have been issued to account for this possibility.

Regardless of how close Erick comes to the close, heavy rainfall and gusty winds are already lashing the coast, and this is expected to continue for another few days as Erick parallels the coast.

5-day intensity forecast

INITIAL 07/05 0300Z 40 KT 45 MPH
12 hour 07/05 1200Z 45 KT 50 MPH
24 hour 07/06 0000Z 50 KT 60 MPH
36 hour 07/06 1200Z 55 KT 65 MPH
48 hour 07/07 0000Z 60 KT 70 MPH
72 hour 07/08 0000Z 65 KT 75 MPH
96 hour 07/09 0000Z 50 KT 60 MPH
120 hour 07/10 0000Z 35 KT 40 MPH

5-day track forecast



Figure 4. My 5-day forecast track for Erick.

NHC storm information

000
WTPZ35 KNHC 050548
TCPEP5

BULLETIN
TROPICAL STORM ERICK INTERMEDIATE ADVISORY NUMBER 3A
NWS NATIONAL HURRICANE CENTER MIAMI FL EP052013
1100 PM PDT THU JUL 04 2013

...RAINBANDS OF ERICK BRUSHING THE PACIFIC COAST OF MEXICO...


SUMMARY OF 1100 PM PDT...0600 UTC...INFORMATION
-----------------------------------------------
LOCATION...14.9N 100.7W
ABOUT 150 MI...240 KM SSW OF ACAPULCO MEXICO
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...NW OR 305 DEGREES AT 12 MPH...19 KM/H
MINIMUM CENTRAL PRESSURE...1004 MB...29.65 INCHES


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

NONE.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* LAZARO CARDENAS TO MANZANILLO

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* ACAPULCO TO EAST OF LAZARO CARDENAS
* WEST OF MANZANILLO TO LA FORTUNA

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 WITHIN THE WATCH AREA.

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 1100 PM PDT...0600 UTC...THE CENTER OF TROPICAL STORM ERICK WAS
LOCATED NEAR LATITUDE 14.9 NORTH...LONGITUDE 100.7 WEST. SATELLITE
DATA INDICATES THAT THE CENTER OF ERICK HAS JOGGED TO THE WEST
DURING THE PAST FEW HOURS. HOWEVER...IT IS EXPECTED TO RESUME A
MOTION TOWARD THE NORTHWEST NEAR 12 MPH...19 KM/H. THIS GENERAL
MOTION IS EXPECTED TO CONTINUE FOR THE NEXT DAY OR SO...FOLLOWED BY
A TURN TOWARD THE WEST-NORTHWEST BY LATE FRIDAY OR SATURDAY. ON THE
FORECAST TRACK...THE CENTER OF ERICK SHOULD MOVE PARALLEL TO...BUT
REMAIN OFFSHORE OF...THE COAST OF SOUTHWESTERN MEXICO.

MAXIMUM SUSTAINED WINDS ARE NEAR 45 MPH...75 KM/H...WITH HIGHER
GUSTS. SOME STRENGTHENING 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 1004 MB...29.65 INCHES.


HAZARDS AFFECTING LAND
----------------------
RAINFALL...ERICK IS EXPECTED TO PRODUCE TOTAL RAIN ACCUMULATIONS OF
3 TO 5 INCHES OVER SOUTHWESTERN OAXACA...SOUTHERN GUERRERO...
SOUTHERN MICHOACA...COLIMA...AND SOUTHERN JALISCO MEXICO...WITH
POSSIBLE ISOLATED MAXIMUM AMOUNTS OF 8 INCHES. THESE RAINS COULD
CAUSE LIFE-THREATENING FLASH FLOODS AND MUD SLIDES.

WIND...TROPICAL STORM CONDITIONS ARE POSSIBLE WITHIN THE WATCH AREA
FROM ACAPULCO TO LAZARO CARDENAS ON FRIDAY. TROPICAL STORM
CONDITIONS ARE LIKELY TO SPREAD WESTWARD INTO THE WARNING AREA
FRIDAY NIGHT AND SATURDAY. TROPICAL STORM CONDITIONS ARE POSSIBLE
WEST OF MANZANILLO BY LATE SATURDAY.


NEXT ADVISORY
-------------
NEXT COMPLETE ADVISORY...200 AM PDT.

$$
FORECASTER BEVEN



Gulf of Mexico disturbance

An area of disturbed weather continues over the Gulf of Mexico, in association with a surface trough interacting with an upper trough over the southern United States. There hasn't been much change to this area over the last 24 hours, and I don't have much else to add. The shower activity that was apparent over the northern Gulf of Mexico earlier on Thursday -- the northern portion of the disturbance -- has largely dissipated, as the developing surface low moved inland over the western Florida panhandle. The southern portion of the disturbance is generating a small area of convection off the northwest coast of the Yucatan Peninsula, where satellite imagery suggests some broad cyclonic turning may be evident near 20N 91W; this would coincide with the 850 mb vorticity maps from CIMSS showing a similar signature.

Surface observations over the Yucatan Peninsula suggest that surface pressures are not falling -- likely due to the lack of convection -- and that the winds are not shifting, so any circulation that might be forming where the satellite/vorticity data suggests it is -- is extremely ill-defined.

A weak upper-level trough over Texas is producing westerly shear over the disturbance, with CIMSS analysis suggesting approximately 20 kt of shear; in fact, the tendency has been for the shear to increase in the last 24 hours. Although the models never really show the shear relaxing enough to allow development, there is some indication that the upper flow may relax a little just before the system moves inland on Saturday, or, more likely, Sunday evening. Given that the system will likely be moving northward by that time, it will be moving roughly in tandem with the shear vector, so there is the potential for this disturbance to attempt a quick spin up just before landfall along the northern Gulf Coast.

Interestingly, the 0z runs of the GFS and CMC suggest that the low-level vorticity associated with the disturbance will split soon, with the western portion moving into the Texas/Mexico border, while the northern portion moves into the northern Gulf Coast. Based on the pattern, I favor a landfall in southeastern Louisiana on Sunday evening, but it could occur a little sooner. The main impact from this system will be heavy rains capable of causing flooding, particularly if this system attempts the quick spin up I think it could; and also the potential for strong coastal winds and flooding.

Although this system may add more rain to already saturated areas of the Alabama/Florida region, the large-scale pattern and shear forecast suggests that the rain will be confined primarily to Louisiana and Mississippi.

Probability of development in 48 hours: 10%

2013 Pacific hurricane season 2013 Atlantic hurricane season Tropical Depression Dalila Tropical Storm Erick

Updated: 6:09 AM GMT on July 05, 2013

Permalink

Tropical weather analysis - July 4, 2013

By: KoritheMan, 6:23 AM GMT on July 04, 2013

Dalila

Dalila continues to weaken under strong vertical shear. As of the latest NHC advisory, the following information was available on the storm:

Wind: 60 mph, with higher gusts
Location: 17.6°N 108.4°W
Movement: W at 5 mph
Pressure: 995 mb

Most of the associated deep convection has been eradicated, likely due to a combination of dry air entrainment and increasing southeasterly shear. In fact, an SSMIS microwave pass just before 3z suggested that the low-level circulation was becoming elongated along a southeast to northwest axis; the pass also suggested that the mid-level center was displaced a little to the northwest of the low-level center. This would be consistent with the continually observed shear.



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

Although convection has redeveloped to the southwest of the center over the past couple of hours, it remains disorganized and shows no signs of wrapping. Given the hostile environment, it seems likely that Dalila will continue to weaken, and it could decay into a remnant low even sooner than indicated in my forecast below. The intensity consensus has come down as well, and my forecast follows it closely.

There is not much to say about the track. Dalila is south of a strong mid-level ridge over the western United States, which is causing the tropical cyclone to move south of west. Most of the models forecast a continued westward motion, but it is hard to see an immediate due westward motion resuming in the short-term given the orientation of the ridge. There are still some differences in timing and movement amongst the models, but overall they have continued to come into better agreement. The tropical disturbance to the east may not be as robust as originally thought, so I am no longer expected Dalila to move cyclonically into the circulation of that low. A turn to the west-northwest is forecast beyond 48 hours as Dalila comes under the influence of a cold low northeast of the Hawaiian Islands, partially associated with the remnants of Hurricane Cosme.

5-day intensity forecast

INITIAL 07/04 0600Z 50 KT 60 MPH
12 hour 07/04 1800Z 40 KT 45 MPH
24 hour 07/05 0600Z 40 KT 45 MPH
36 hour 07/05 1800Z 35 KT 40 MPH
48 hour 07/06 0600Z 35 KT 40 MPH
72 hour 07/07 0600Z 30 KT 35 MPH...POST-TROPICAL/REMNANT LOW
96 hour 07/08 0600Z 30 KT 35 MPH...POST-TROPICAL/REMNANT LOW
120 hour 07/09 0600Z 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW

5-day track forecast



Figure 2. My 5-day forecast track for Dalila.



Invest 97E

An area of disturbed weather located a few hundred miles south-southeast of Acapulco, Mexico continues to produce disorganized showers and thunderstorms. The system appears to have lost some organization since yesterday, although ASCAT data from earlier on Wednesday suggested that the surface circulation was still respectable. Based on the cloud motions on shortwave infrared satellite imagery, I feel that the earlier ASCAT pass did not properly resolve the circulation associated with this disturbance, giving it more credit than it deserves.



Figure 3. Latest infrared satellite image of Invest 97E. Image credit: NOAA's Satellite Services Division (SSD).

The cloud pattern still suggests easterly shear associated with a mid-level ridge over the northwestern Caribbean. The global models have differing solutions on the evolution of the upper air pattern and how favorable the shear becomes, but in general they have been trending toward stronger shear over the last 24 hours. Based on current trends, there is still some potential for this low to become a tropical depression over the next few days as it moves generally west-northwest at about 15 mph, parallel to the Mexican coast. It is possible that future forecasts will have to trend downward on development potential if the shear continues, and the system does not become any better organized.

Probability of development in 48 hours: 60%



Gulf of Mexico disturbance

A large area of cloudiness and thunderstorms continues over the Yucatan Peninsula and much of the southern and central Gulf of Mexico extending into the northwestern Caribbean Sea. I remain unimpressed by this system so far, with little evidence of large-scale pressure falls or cyclonic wind shifts. While the shear appears to be slowly decreasing over the southern Gulf, there is still plenty of it. The global models forecast an environment over the Gulf that never becomes particularly conducive for development, with southwesterly shear evident, and very little evidence of an anticyclone. While this diffluent upper pattern would likely sustain strong convective activity to the east of the modeled surface low, it would also entrain dry air into the circulation and not allow for much in the way of tropical organization.

This system is large and complex, and the northern portion of the system is likely to move into the western Florida panhandle by Thursday evening.

It should be noted that the primary hazard associated with this large conglomeration of disturbed weather is the potential for heavy rains and inland flooding through the weekend. The southern portion of the disturbance is still over the Yucatan Peninsula, and is embedded in very weak steering between two anticyclones and a large-amplitude trough over the central United States. The models maintain this flow pattern over the next couple of days, but the system is still forecast to move over the Bay of Campeche in the next 24-36 hours. Beyond that time, if the upper air pattern cooperates, we could see the potential for some organization from this system, although again, with the model forecasts of strong shear, it is difficult to see this making much in the way of tropical accolades. The southern portion of the system is forecast to move inland over western or west-central Louisiana on Sunday or Monday.

Probability of development in 48 hours: 10%

2013 Pacific hurricane season 2013 Atlantic hurricane season Tropical Storm Dalila Invest 97E

Permalink

Tropical weather analysis - July 3, 2013

By: KoritheMan, 7:03 AM GMT on July 03, 2013

Dalila

Dalila strengthened into the third hurricane of the 2013 Pacific hurricane season on Monday afternoon. As of the latest NHC advisory, the following information was available on the hurricane:

Wind: 75 mph, with higher gusts
Location: 18.3°N 107.3°W
Movement: W at 2 mph
Pressure: 987 mb
Category: 1 (Saffir-Simpson Hurricane Wind Scale)

Dalila continues generating rather cold cloud tops, but a couple of recent microwave passes show a deterioration of the inner core structure, the eyewall open to the east. There is a good bit of southeasterly shear over the hurricane, apparently related to a mid-level ridge over the northwestern Caribbean Sea, and also perhaps aided a little by a developing disturbance to the east, although that might be too far away to directly influence Dalila in the short-term.



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

Dalila has been consistently moving south of the original forecast tracks, which has kept the hurricane over warmer water. While this would normally argue for additional intensification, the global models suggest a continuation of the current shear pattern, and this is favored by glancing at water vapor images as well. The SHIPS suggests the shear will increase further near the end of the period, which would also exacerbate the weakening process. Thus, the forecast calls for steady weakening of the hurricane after 24 hours, with a somewhat more abrupt pace expected at the end of the period.

Water vapor and synoptic data suggest a small kink has developed in the western United States death ridge in association with a small upper trough over western California; this has successfully altered the ridge's orientation such that Dalila appears to now be moving in a west-southwesterly to southwesterly direction, seen using a blend of the various satellite and microwave fixes. There is still some disagreement amongst the models, with the GFS continuing to call for a generally westward-moving cyclone until dissipation, while the ECMWF continues to postulate a more erratic motion; however, it should be pointed out that these models seem to have come into better agreement compared to 24 hours ago, which increases confidence in the forecast. There is still a considerable amount of uncertainty, though, particularly at longer ranges as we wait to see how Dalila interacts with the developing disturbance to the east. It is my feeling that Dalila's vortex will have sufficiently wound down during the end of the forecast period so that the secondary vortex -- then strengthening tropical cyclone -- will begin to nudge the cyclone toward the southeast as Dalila comes under the low-level cyclonic westerly flow associated with the secondary feature.

5-day intensity forecast

INITIAL 07/03 0600Z 65 KT 75 MPH
12 hour 07/03 1800Z 65 KT 75 MPH
24 hour 07/04 0600Z 65 KT 75 MPH
36 hour 07/04 1800Z 60 KT 70 MPH
48 hour 07/05 0600Z 55 KT 65 MPH
72 hour 07/06 0600Z 45 KT 50 MPH
96 hour 07/07 0600Z 35 KT 40 MPH
120 hour 07/08 0600Z 30 KT 35 MPH

For some reason, I'm having trouble posting my track map tonight, so we'll go without one for this forecast package. I apologize.


Invest 97E

An area of low pressure located a few hundred miles south of Salina Cruz, Mexico is gradually becoming better organized. While the convection is still broad and unfocused, there has been some subtle hints of convective banding, particularly to the east, and now to the west, where a large and newly-developed band has formed.



Figure 2. Latest infrared satellite image of Invest 97E. Image credit: NOAA's Satellite Services Division (SSD).

There is still some easterly shear over the system, but all of the global models steadily relax this flow over the next 48 hours, which should allow the system to slowly develop. I am anticipating this system to become a tropical cyclone in the next three to four days, and it could occur at the lower end of the estimate if the rate of organization begins to increase. The models suggest this low will move west-northwestward parallel to the coast of Mexico over the next several days, with the possibility of a more northwesterly turn as the system nears the southwest coast of Mexico. It is too early to determine whether or not this system moves inland or not.

Probability of development in 48 hours: 60%



Yucatan Peninsula disturbance


A large area of disturbed weather has developed over the Yucatan Peninsula and western Caribbean Sea, likely in connection with the northern portion of the tropical wave that is poised to produce Tropical Storm Erick in the eastern Pacific. Surface observations and satellite data suggest that the actual surface trough is probably centered over the central Yucatan Peninsula between Campeche and Chetumal, moving slowly west-northwest. Surface pressures are not falling in the western Caribbean Sea, but were relatively low at Merida, Mexico over the last hour, which suggests that the main focus for convergence and thunderstorms is over the Yucatan Peninsula.

The system is in an area of weak steering, with a ridge over the western United States, a cold low/trailing upper trough over the central and southern United States, and another ridge over the western Atlantic and southeastern United States. The global models do not show much change in this pattern for the next two days or so, and it is my expectation that this system will move only slowly over the next couple of days, emerging into the Gulf of Mexico/northern Bay of Campeche in about a day or so. Afterward, the models suggest more progression to the pattern, with the cold low and its attendant trough moving slowly eastward and amplifying southward; this is expected to move the system into the northern or central Gulf Coast by this weekend. The latest I would see the system moving inland is Monday afternoon, and that's likely being generous.

The 0z CMC shows this system moving into southeastern Texas in 96 hours, while the 0z GFS shows it moving into west-central Louisiana in 120 hours. Based on the pattern favoring a slower motion, coupled with the strength of the western United States ridge, I tend to favor the latter solution.

The global models suggest the current westerly shear over the system will gradually relax through the weekend, and the CMC and GFS develop an anticyclone over the system as it approaches the coast, which would promote an environment of light shear. However, the environment never becomes ideal for strengthening, with some southwesterly shear still remaining, and it is possible that the purported anticyclones will become dislodged amidst this flow. Given how little we know about tropical cyclone intensity change, however, I would anticipate anything from a rainy blob to a formidable tropical storm.

Regardless of eventual development, this system is likely to bring a swath of heavy rains and possible coastal flooding to portions of the northern Gulf Coast over the weekend. Interests from Louisiana to the Florida panhandle should monitor the progress of this system. Texas should monitor it as well, but again, given the pattern and the ridge over the western United States, I don't see this making much westward progress, especially since it will be on the back side of the southern United States upper trough as well.

Probability of development in 48 hours: 10%

2013 Pacific hurricane season 2013 Atlantic hurricane season Hurricane Dalila Invest 97E

Updated: 7:15 AM GMT on July 03, 2013

Permalink

Tropical weather analysis - July 2, 2013

By: KoritheMan, 4:32 AM GMT on July 02, 2013

Dalila

Tropical Storm Dalila is just under hurricane strength. As of the most recent NHC advisory, the following information was made on the storm:

Wind: 70 mph, with higher gusts
Location: 18.2°N 106.9°W
Moving: WNW at 6 mph
Pressure: 992 mb

The satellite presentation consists of a small but well-defined central dense overcast with cold convection. Most of the convective banding that was seen earlier has loosened and morphed into the CDO, although a formative curved band is beginning to redevelop in the western semicircle of the cyclone circulation. Recent microwave data suggests a narrow warm spot surrounded by a fragmented eyewall.



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

Water vapor imagery still suggests some southeasterly shear over Dalila, which is contributing to the somewhat asymmetric appearance of the convection in that quadrant. The global models suggest that the shear will soon change to southerly, but will remain in at least the 15 to 20 kt range throughout much of the forecast period; this is expected to mitigate any significant strengthening despite of warm sea surface temperatures for the next three or so days. In addition, water vapor imagery and analysis of the SHIPS model file suggests that Dalila will soon encounter a much drier airmass, which should also help to exacerbate the weakening process. Late in the period, Dalila is forecast to encounter the 26C isotherm, although if the forecast track continues to shift to the south, the cyclone will remain over warmer water and would likely weaken more slowly. In the meantime, there is still a little more time for intensification, and my forecast shows Dalila peaking at 70 kt over the next day or so, and remains at the upper end of the guidance envelope. An alternate scenario is that Dalila does not strengthen anymore, as a microwave pass just after 3z shows that the inner core and developing eye has collapsed. It is possible the shear is getting to it faster than I thought.

Dalila remains south of a strong mid-level ridge over the western United States. With the help of a couple passive microwave images, it appears that the tropical cyclone has been gradually turning to the left as it fully comes underneath the influence of the ridge. A definite westward motion should soon ignite, but there remains a considerable dichotomy between the models, with the GFS continuing to take Dalila slowly westward throughout the forecast period, but even that model shows something of a southwestward bend beyond Wednesday afternoon. The ECMWF continues to abruptly turn Dalila southwest in about 24 hours, while the GFDL erratically takes the storm over southern Baja. What this suggests is that there will likely be little overall movement of the tropical cyclone, particularly in the near-term. Later in the period, some acceleration is shown relative to earlier forecast times, but is held slower than the National Hurricane Center forecast just in case some erratic motion occurs later in the period. I am unsure why the discrepancy, but I presume it is related to the depth of the cyclone vortex, with the ECMWF showing a weaker cyclone. For now, the stronger solution is preferred, but if the southward movement turns out to be reality, additional southward adjustments will become necessary in later forecast packages.

Because Dalila is turning away from Mexico, all coastal watches and warnings have been discontinued. However, locally heavy rain and high surf will continue to impact a portion of the southwest coast for the next day or so.


5-day intensity forecast

INITIAL 07/02 0300Z 60 KT 70 MPH
12 hour 07/02 1200Z 65 KT 75 MPH
24 hour 07/03 0000Z 70 KT 80 MPH
36 hour 07/03 1200Z 65 KT 75 MPH
48 hour 07/04 0000Z 60 KT 70 MPH
72 hour 07/05 0000Z 50 KT 60 MPH
96 hour 07/06 0000Z 40 KT 45 MPH
120 hour 07/07 0000Z 30 KT 35 MPH

5-day track forecast



Figure 2.
My 5-day forecast track for Dalila.



Invest 97E

An area of disturbed weather located a couple hundred miles south of the extreme southeast coast of Mexico is association with a tropical wave. The system is currently experiencing easterly shear, but these winds are forecast to slowly relax over the next 48 hours, which should allow for steady development beyond that time. Most of the makes this system into a tropical cyclone in a few days as it moves west to west-northwest at 10 to 15 mph.

Probability of development in 48 hours: 10%



Elsewhere

The GFS has been hinting at the possibility of a trough split occurring over the western Atlantic late this week into early next week, in association with a large baroclinic zone east of Bermuda; the southern portion of this feature breaks off due to ridging and begins to move westward toward the Bahamas. However, this solution has been very inconsistent. The CMC made this system into a hurricane that made landfall in southeast Louisiana during the 0z run on Sunday, but this solution seems highly improbable, and the model has since dropped it. Interestingly, that model also wants to bring a tropical cyclone into the Florida panhandle in about 3 or 4 days; this system comes from the northern portion of the tropical wave over Hispaniola as it moves west-northwestward under the ridge into the Gulf. None of the other models show this, and this is probably just the CMC spewing crap again.

All things considered, the Atlantic remains quiet for now, with the upward MJO pulse likely in the process of leaving our area of the world. It is still my expectation that activity will pick up in the next couple weeks as the Bermuda high weakens and allows for more convergence in the MDR, but this is speculative for now.

2013 Pacific hurricane season Tropical Storm Dalila Invest 97E 2013 Atlantic hurricane season

Updated: 4:34 AM GMT on July 02, 2013

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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.