KoritheMan's WunderBlog

Tropical weather analysis - August 31, 2013

By: KoritheMan, 7:05 AM GMT on August 31, 2013

Invest 96L

A vigorous tropical wave is located just off the west coast of Africa ("96L"). Satellite images show a healthy burst of thunderstorm activity located to the west of the low-level center due some easterly shear, which is typical of tropical cyclones and tropical waves in this location.

Upper-level winds appear to be conducive for some steady development of this wave over the next 48 hours, with the GFS suggesting that the environment may even become broadly anticyclonic. However, the wave may cross the 26C isotherm in as little as 36 hours, since it is at a latitude where a more northerly track is reasonable; shear is also forecast to increase in about 72 hours, which could combine with the cool waters to discourage development beyond that time.

Based on the synoptic pattern over the east coast and the more northerly emergence of this wave from the coast of Africa, I am not expecting this wave to be a threat to any land areas down the road, probably not even Bermuda.

Probability of development in 48 hours: 50%



Elsewhere, a tropical wave is moving westward several hundred miles east of the Lesser Antilles. Upper-level winds could become a little more favorable in a few days when the wave reaches the eastern Caribbean Sea, so it will need to be monitored for possible convective resurgence and organization at that point.

Probability of development in 48 hours: 0%



Tropical Depression Eleven-E

Tropical Depression Eleven-E formed in the east Pacific well southwest of the Baja Peninsula Friday evening. As of the 0300Z NHC advisory, the following information was posted on the storm:

Wind: 35 mph, with higher gusts
Location: 18.3°N 115.9°W
Movement: NNW at 7 mph
Pressure: 1006 mb

Convective banding associated with the cyclone has been increasing to the south, and there has been a small increase in central convection, but the low-level center appears to be along the northern edge of the convective mass. There appears to be some northerly shear afflicting the depression, judging by high cloud vectors on water vapor imagery.



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

The shear is not expected to be enough to prohibit at least modest strengthening, but the near-storm dry air environment argues against rapid strengthening even if the shear eases up a little. The depression is forecast to become a tropical storm within the next 12 hours, and reach a peak intensity of 40 kt in about 36 hours; this is a little higher than the current NHC intensity scheme. Beyond 48 hours, the cyclone is forecast to traverse cooler waters, and the GFS hints at a possible increase in southwesterly shear during the latter portion of the forecast period. Weakening is forecast to begin at day three and beyond, with the depression forecast to degenerate into a remnant low on day five.

The location and motion of the depression are not easy to determine this morning, as I am lacking adequate microwave data, but as best I can tell, which may not be very well, it remains on track. The guidance is in general agreement on a gradual turn to the north over the next 24-36 hours, with substantial differences thereafter in whether the cyclone continues northward or meanders southward. I agree with the National Hurricane Center that the depression should be fairly shallow near the end of the period, which would tend to favor the more southern track. In deference to the possibility that both solutions may materialize to some extent, my forecast shows the southward dip earlier than the forecast from the NHC. What will actually happen remains to be seen.

Intensity forecast and positions

INITIAL 08/31 0300Z 18.3°N 115.9°W 30 KT 35 MPH
12 hour 08/31 1200Z 18.7°N 116.3°W 35 KT 40 MPH
24 hour 09/01 0000Z 19.4°N 116.6°W 40 KT 45 MPH
36 hour 09/01 1200Z 19.9°N 116.8°W 45 KT 50 MPH
48 hour 09/02 0000Z 20.4°N 116.9°W 45 KT 50 MPH
72 hour 09/03 0000Z 20.7°N 116.9°W 35 KT 40 MPH
96 hour 09/04 0000Z 20.6°N 117.1°W 30 KT 35 MPH
120 hour 09/05 0000Z 20.5°N 117.2°W 30 KT 35 MPH...POST-TROPICAL/REMNANT LOW

Track forecast



Figure 2. My forecast track for TD Eleven-E.

2013 Atlantic hurricane season 2013 Pacific hurricane season Invest 96L Tropical Depression Eleven-E

Updated: 7:08 AM GMT on August 31, 2013

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Tropical weather analysis - August 29, 2013

By: KoritheMan, 5:45 AM GMT on August 29, 2013

Juliette

Tropical Storm Juliette quickly spun up today off the coast of Baja California. As of the just released NHC intermediate advisory, the following information was provided on the cyclone:

Wind: 45 mph, with higher gusts
Location: 23.8°N 111.0°W
Movement: NW at 23 mph
Pressure: 998 mb

Convection has been increasing in the last few hours, with the center more or less along the northern portion of the shower activity, not completely exposed but not quite under the deep convection, either. The 0z estimates from TAFB and SAB do not currently support tropical storm strength, but based on a 1600 UTC ASCAT pass showing believable 35 kt wind vectors, and the recent increase in central convection, there appears to be little reason to assume Juliette has dropped below tropical storm strength over the last few hours. In fact, the intermediate advisory suggests Juliette has actually strengthened, which is not unbelievable given the cloud pattern. The 06z Dvorak numbers will be most interesting, since the 0z classifications were made during a convective lull.



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

A couple of microwave fixes suggest that Juliette continues to move rather quickly toward the northwest along the southwestern periphery of a strong ridge over the southwestern United States. Water vapor imagery shows a mid- to upper-level trough amplifying and moving southward off the west coast of the United States, an evolution which is expected to steer Juliette northwestward and then west-northwestward. This will force an interaction with the rugged terrain of the Baja peninsula, which should induce weakening. Additionally, Juliette will cross the 26C isotherm in about a day or less, which will significantly hasten the decaying progress in spite of the relatively low vertical wind shear environment. Given that Juliette is a very small tropical storm, it could certainly weaken faster than indicated below. Juliette is expected to lose its luster as a tropical cyclone in about 24 hours, with complete dissipation beyond 48 hours. The guidance envelope has shifted a little westward between 18z and 0z, and my forecast track is a little to the left of the current NHC prediction, but follow the same synoptic reasoning.

There have been no reports of tropical storm force winds, sustained in or gusts, in connection with Juliette, offshore or overland. While tropical storm warnings are reasonably posted for the southern portion of the Baja Peninsula pending further notice, I sincerely doubt that these winds will become sustained at that strength along the coast, particularly if my more westward forecast track proves itself to be correct. Interests in the warning area should closely monitor the progress of Juliette over the next 12-24 hours, as any deviation to the right would bring those winds ashore the immediate coastal areas. It should also be noted that tropical storm force winds could be occurring over areas of higher terrain.

Locally heavy rainfall and possible flooding are also anticipated, particularly in areas of higher terrain.

Intensity forecast and positions

INITIAL 08/29 0300Z 23.0°N 110.1°W 45 KT 50 MPH
12 hour 08/29 1200Z 24.7°N 112.2°W 35 KT 40 MPH
24 hour 08/30 0000Z 26.1°N 114.5°W 30 KT 35 MPH
36 hour 08/30 1200Z 26.6°N 117.3°W 25 KT 30 MPH
48 hour 08/31 0000Z 26.8°N 119.9°W 20 KT 25 MPH...POST-TROPICAL/REMNANT LOW
72 hour 09/01 0000Z...DISSIPATED

Track forecast



Figure 2. My forecast track for Juliette.

NHC storm information

000
WTPZ35 KNHC 290532
TCPEP5

BULLETIN
TROPICAL STORM JULIETTE INTERMEDIATE ADVISORY NUMBER 2A
NWS NATIONAL HURRICANE CENTER MIAMI FL EP102013
1100 PM PDT WED AUG 28 2013

...JULIETTE A LITTLE STRONGER AS IT PASSES JUST OFFSHORE THE WEST
COAST OF BAJA CALIFORNIA SUR...


SUMMARY OF 1100 PM PDT...0600 UTC...INFORMATION
-----------------------------------------------
LOCATION...23.8N 111.0W
ABOUT 95 MI...150 KM NW OF CABO SAN LUCAS MEXICO
ABOUT 105 MI...170 KM SE OF CABO SAN LAZARO MEXICO
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...NW OR 315 DEGREES AT 23 MPH...37 KM/H
MINIMUM CENTRAL PRESSURE...999 MB...29.50 INCHES


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

NONE.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* THE COAST OF THE BAJA CALIFORNIA PENINSULA FROM SAN EVARISTO TO
BAHIA MAGDALENA...INCLUDING CABO SAN LUCAS

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 TROPICAL STORM JULIETTE
WAS LOCATED NEAR LATITUDE 23.8 NORTH...LONGITUDE 111.0 WEST.
JULIETTE IS MOVING TOWARD THE NORTHWEST NEAR 23 MPH...37 KM/H...AND
THIS MOTION WITH A REDUCTION IN FORWARD SPEED IS EXPECTED DURING
THE NEXT DAY OR SO. A TURN TOWARD THE WEST-NORTHWEST WITH AN
ADDITIONAL DECREASE IN FORWARD SPEED IS FORECAST ON THURSDAY NIGHT.
ON THE FORECAST TRACK...THE CENTER OF JULIETTE WILL CONTINUE TO
MOVE NEAR OR ALONG THE WEST COAST OF THE SOUTHERN BAJA CALIFORNIA
PENINSULA OVERNIGHT AND EARLY THURSDAY.

WIND REPORTS FROM THE SOUTHERN BAJA CALIFORNIA PENINSULA INDICATE
THAT MAXIMUM SUSTAINED WINDS ARE NEAR 50 MPH...85 KM/H...WITH
HIGHER GUSTS. STRONGER WINDS ARE LIKELY OCCURRING OVER AREAS OF
HIGHER TERRAIN ON THE SOUTHERN BAJA CALIFORNIA PENINSULA.
WEAKENING IS FORECAST DURING THE NEXT 48 HOURS...AND JULIETTE IS
EXPECTED TO WEAKEN TO A DEPRESSION LATE THURSDAY OR THURSDAY NIGHT.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 45 MILES...75 KM...
MAINLY TO THE EAST OF THE CENTER. DURING THE PAST SEVERAL HOURS...
AN ELEVATED STATION AT CABO PULMO MEXICO REPORTED A SUSTAINED WIND
OF 57 MPH...92 KM/HR...AND A WIND GUST OF 76 MPH...122 KM/HR.

THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 999 MB...29.50 INCHES. AN
UNOFFICIAL STATION AT EL PESCADERO MEXICO RECENTLY REPORTED A
MINIMUM PRESSURE OF 1001 MB...29.56 INCHES.


HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM CONDITIONS ARE OCCURRING OVER THE SOUTHERN
PORTION OF THE WARNING AREA...AND ARE EXPECTED TO SPREAD NORTHWARD
THROUGH THE REMAINDER OF THE WARNING AREA OVERNIGHT.

RAINFALL...JULIETTE IS EXPECTED TO PRODUCE TOTAL RAIN ACCUMULATIONS
OF 1 TO 3 INCHES OVER SOUTHERN PORTIONS OF THE BAJA CALIFORNIA
PENINSULA.


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

$$
FORECASTER BERG/BRENNAN



Invest 97E

An area of low pressure is located well to the southwest of Juliette, about midway between the Hawaiian Islands and the southwestern tip of the Baja Peninsula. Shower activity has increased a little near this low over the last couple of hours, and the GFS suggests the upper-level wind pattern could become a little more conducive for development over the next couple of days. However, the system will be approaching cooler water beyond day three, so the chances of this ultimately becoming a tropical cyclone don't appear to be terribly high.

This low is expected to move generally northward over the next couple of days.

Probability of development in 48 hours: 20%

2013 Pacific hurricane season Tropical Storm Juliette Invest 97E

Updated: 5:55 AM GMT on August 29, 2013

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Tropical weather analysis - August 26, 2013

By: KoritheMan, 5:11 AM GMT on August 26, 2013

Fernand

Tropical Storm Fernand is making landfall along the coast of Mexico just north of Veracruz, Mexico. As of the latest NHC advisory, the following information was available on Fernand:

Wind: 50 mph, with higher gusts
Location: 19.3°N 96.2°W
Movement: W at 9 mph
Pressure: 1001 mb

The intensity of Fernand is difficult to estimate this evening. The last reconnaissance flight was several hours ago, when the aircraft found flight-level winds of 52 kt in the northwest quadrant during their outbound leg. Satellite intensity estimates do not really support an intensity higher than about 40 kt, but a couple of observing stations off the coast of Veracruz reported sustained winds near 45 kt with gusts approaching hurricane force a couple of hours ago. The small wind field suggests possibility that the offshore observing stations missed the core of strongest winds, and a recent raw ADT estimate of 4.0 is indicative of a minimal hurricane. In addition, a couple of successful microwave passes during the evening showed a large eye structure surrounded by what appeared to be a primitive eyewall, which was reaffirmed by doppler radar data from Alvarado. While my hunch is that Fernand is a little bit stronger than the operational estimates from the National Hurricane Center suggest, Dvorak constraints and a lack of conclusive observations in the vicinity of the cyclone center dictates that the agency remain understandably conservative.



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

Although the coordinates given above show Fernand still offshore, it has been over two hours since the release of the 0300Z advisory, and a blend of satellite, surface, radar, and microwave fixes suggest that Fernand has moved inland. The tropical storm is expected to move west to west-northwest until dissipation over the Sierra Madre mountain range in about 36 hours. Fernand is a very small circulation, so it is possible that the dissipation could occur a little sooner.

Station SAC4 off the coast of Veracruz was reporting sustained winds of 35 kt with gusts to 43 kt at 10:00 PM local time. Although the winds in this area have likely diminished below tropical storm force, wind gusts to that strength are likely still afflicting the immediate coastal waters, with the sustained tropical storm force winds likely just inland from the coast. These winds will quickly subside as Fernand moves into higher terrain in the next few hours, but the threat of very heavy rains and flash flooding will continue even long after Fernand has dissipated as a tropical cyclone.

Intensity forecast and positions

INITIAL 08/26 0300Z 19.3°N 96.2°W 45 KT 50 MPH
12 hour 08/26 1200Z 19.5°N 97.4°W 35 KT 40 MPH...INLAND
24 hour 08/27 0000Z 19.8°N 98.7°W 25 KT 30 MPH...INLAND
36 hour 08/27 1200Z 20.3°N 100.1°W 20 KT 25 MPH...INLAND POST-TROPICAL/REMNANT LOW
48 hour 08/28 0000Z...DISSIPATED

Track forecast



Figure 2. My forecast track for Fernand.

NHC storm information

000
WTNT31 KNHC 260235
TCPAT1

BULLETIN
TROPICAL STORM FERNAND ADVISORY NUMBER 3
NWS NATIONAL HURRICANE CENTER MIAMI FL AL062013
1000 PM CDT SUN AUG 25 2013

...FERNAND CONTINUES TO STRENGTHEN...
...TROPICAL-STORM-FORCE WINDS LASHING VERACRUZ HARBOR...


SUMMARY OF 1000 PM CDT...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...19.3N 96.2W
ABOUT 5 MI...10 KM N OF VERACRUZ MEXICO
ABOUT 140 MI...225 KM SE OF TUXPAN MEXICO
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 9 MPH...15 KM/H
MINIMUM CENTRAL PRESSURE...1001 MB...29.56 INCHES


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

THE GOVERNMENT OF MEXICO HAS DISCONTINUED THE TROPICAL STORM WARNING
FOR THE GULF COAST OF MEXICO NORTH OF BARRA DE NAUTLA.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* GULF COAST OF MEXICO FROM VERACRUZ NORTHWARD TO BARRA DE NAUTLA

A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA...IN THIS CASE WITHIN THE
NEXT 6 HOURS.

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


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 1000 PM CDT...0300 UTC...THE CENTER OF TROPICAL STORM FERNAND WAS
LOCATED NEAR LATITUDE 19.3 NORTH...LONGITUDE 96.2 WEST. FERNAND IS
MOVING TOWARD THE WEST NEAR 9 MPH...15 KM/H. A WESTWARD TO
WEST-NORTHWESTWARD MOTION WITH SOME DECREASE IN FORWARD SPEED IS
EXPECTED OVER THE NEXT DAY OR SO. ON THE FORECAST TRACK...THE
CENTER SHOULD MOVE ACROSS THE VERACRUZ METROPOLITAN AREA TONIGHT...
AND MOVE INLAND OVER MEXICO BY EARLY MONDAY MORNING.

REPORTS FROM AN AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT AND
OBSERVING STATIONS IN VERACRUZ MEXICO INDICATE THAT MAXIMUM
SUSTAINED WINDS HAVE INCREASED TO NEAR 50 MPH...85 KM/H...WITH
HIGHER GUSTS. SOME ADDITIONAL STRENGTHENING IS POSSIBLE BEFORE
FERNAND MAKES LANDFALL ALONG THE GULF COAST OF MEXICO EARLY MONDAY
MORNING. WEAKENING WILL BEGIN AFTER THE CENTER MOVES INLAND.

TROPICAL-STORM-FORCE WINDS EXTEND OUTWARD UP TO 35 MILES...55 KM
FROM THE CENTER. TWO MEXICAN COASTAL WEATHER OBSERVING SITES IN
VERACRUZ HARBOR RECENTLY REPORTED SUSTAINED WINDS OF AT LEAST 50
MPH...85 KM/H WITH GUSTS UP TO 72 MPH...117 KM/H.

THE ESTIMATED MINIMUM CENTRAL PRESSURE...BASED ON NEARBY SURFACE
OBSERVATIONS...IS 1001 MB...29.56 INCHES.


HAZARDS AFFECTING LAND
----------------------
RAINFALL...TROPICAL STORM FERNAND IS EXPECTED TO PRODUCE 4 TO 8
INCHES OF RAIN OVER VERACRUZ...HIDALGO...NORTHERN PUEBLA...SOUTHERN
TAMAULIPAS...AND EASTERN SAN LUIS POTOSI MEXICO...WITH ISOLATED
MAXIMUM AMOUNTS NEAR 12 INCHES POSSIBLE. THESE RAINS COULD CAUSE
LIFE-THREATENING FLASH FLOODS AND MUD SLIDES.

WIND...TROPICAL STORM CONDITIONS ARE SPREADING OVER THE COASTAL
AREAS OF THE MEXICAN STATE OF VERACRUZ.


NEXT ADVISORY
-------------
NEXT INTERMEDIATE ADVISORY...100 AM CDT.
NEXT COMPLETE ADVISORY...400 AM CDT.

$$
FORECASTER STEWART/KIMBERLAIN

2013 Atlantic hurricane season Tropical Storm Fernand

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Tropical weather analysis - August 17, 2013

By: KoritheMan, 5:57 AM GMT on August 17, 2013

Erin

After briefly weakening to a tropical depression on Friday, Erin has regained tropical storm strength as of the latest NHC advisory:

Wind: 40 mph, with higher gusts
Location: 18.5°N 34.5°W
Movement: NW at 16 mph
Pressure: 1006 mb

Although there is now deep convection -- unlike 12 hours ago -- the satellite presentation of Erin is not impressive, with the cyclone center located a little to the southwest of the deep convection, possibly due to a little bit of southwesterly shear and the entrainment of drier air.



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

Erin's future looks rather bleak, to say the least. The SHIPS model and areal SST analyses suggest that the tropical storm is underneath some rather marginal water temperatures. That, combined with the large-scale subsidence over the central tropical Atlantic, argues against the prospects for strengthening. And, while the projected track of the cyclone takes it across notably warmers at 72 hours at beyond, the GFS shows westerly to southwesterly vertical shear increasing over the next couple of days and extending to beyond the end of the forecast period, likely in response to a temporary restrengthening of the semipermanent mid-oceanic trough, depicted rather identifiably on water vapor images. While the core of strongest shear may stay just west of Erin, the upper flow in the near-storm environment will still be strong enough to inject a comparably drier airmass into the circulation, exacerbating the detrimental effects of the shear. Most of the guidance opens Erin up into a tropical wave within the next few days, and my forecast shows dissipation a day earlier than the one by the National Hurricane Center. It would certainly be no surprise if Erin met its end even sooner than that.

Erin took a turn to the northwest over the last 12 hours, due to a break in the subtropical ridge created by a persistent upper low moving westward southwest of the Azores. The global models suggest this feature will gradually retreat northward over the next couple of days, which could allow for a brief restrengthening of the subtropical ridge to the north. After that time, the models show a second break developing in the ridge near 50W, possibly associated with a second cold low well northeast of the Lesser Antilles being reinforced by distant shortwave impulses riding through the westerlies at longer ranges. Storms in Erin's location rarely go on to affect land, and I am now completely apt to buy the recurvature solution, likely well to the east of even Bermuda.

Intensity forecast and positions

INITIAL 08/17 0300Z 18.5°N 34.5°W 35 KT 40 MPH
12 hour 08/17 1200Z 19.5°N 36.0°W 35 KT 40 MPH
24 hour 08/18 0000Z 20.5°N 38.4°W 30 KT 35 MPH
36 hour 08/18 1200Z 20.9°N 40.6°W 30 KT 35 MPH
48 hour 08/19 0000Z 21.4°N 43.0°W 30 KT 35 MPH
72 hour 08/20 0000Z 22.1°N 47.2°W 25 KT 30 MPH
96 hour 08/21 0000Z...DISSIPATED

Track forecast



Figure 2. My forecast track for Erin.

Invest 92L

A broad area of low pressure centered over the southwestern Gulf of Mexico about 130 miles west-southwest of Campeche, Mexico. Satellite images show that the associated shower activity is very poorly-organized, with any convection located well to the east and northeast of the center.



Figure 3. Latest infrared satellite image of Invest 92L. Image credit: NOAA's Satellite Services Division (SSD).

I had hypothesized earlier that a new center was attempting to form to the northwest of the Yucatan Peninsula, near 22N 90W, but a timely 0230 UTC ASCAT pass showed nothing but southeasterlies in that area, signifying that whatever vorticity maximum exists in that area is entirely mid-level. The actual low-level center, devoid of convection, has drifted southward to around 20.3N 92.5W. There is a shortwave trough moving through the northern Gulf Coast, while a ridge is nosing southward into the western Gulf of Mexico. This pattern favors the more westward track the models have been indicating over the last 24 hours, and with sufficient evidence to lean in that direction myself, I will go ahead and do that now. 92L is expected to move west-northwest to northwest and arrive at the coast of northeastern Mexico or south Texas in about 72 hours. The upper cold low appears to have flattened quite a bit, which could provide a more favorable upper-level environment for 92L to attempt to develop prior to reaching the western Gulf Coast. However, water vapor images show a large area of dry air covering the western Gulf of Mexico, which might mitigate the improving upper-level winds, especially if the flow remains northerly to northwesterly behind the Gulf Coast shortwave, which would be supported in a pattern like this.

I am not as impressed for development prospects as I was a few days ago. However, the 300 mb pattern could still favor a heavy rain episode for the northern Gulf Coast as the mid-level circulation alluded to earlier continues to stretch out and elongate, even if the actual center stays well to the west.

Probability of development in 48 hours: 30%

Tropical Storm Erin Invest 92L

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Tropical weather analysis - August 16, 2013

By: KoritheMan, 7:48 AM GMT on August 16, 2013

Erin

Tropical Storm Erin continues across the central Atlantic. As of the soon to be replaced 0300Z NHC advisory, the following information was available on this cyclone:

Wind: 40 mph, with higher gusts
Location: 15.5°N 29.1°W
Movement: WNW at 15 mph
Pressure: 1007 mb

Deep convection had eroded earlier in the day on Thursday; analysis of CIMSS MIMIC-TPW animation suggests that some dry air could have gotten entrained into the cyclone circulation. Since that time, Erin has regained some central convection, although it is not particularly organized. Satellite classifications still support minimal tropical storm strength, and a 0z OSCAT pass showed believable tropical storm force wind vectors.



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

The intensity forecast for Erin is tricky. On one hand, the cyclone is approaching the diurnal convective maximum; since Erin is still a weak system, it is more apt to respond to that mechanism than a more mature tropical cyclone would, which suggests some intensification could occur overnight. On the other hand, the cyclone did entrain some drier air yesterday, which, although not readily depicted on water vapor imagery at this time, could be easily missed by that tool. Another negative factor is the marginal sea surface temperatures Erin is over, barely 26C. Since the shear is low and there is a healthy moisture shield to the south within the Intertropical Convergence Zone, I presume that the more favorable conditions will win out and counteract that marginal thermodynamics, allowing Erin to strengthen over the next 24 hours. Beyond that time, even cooler waters and an increase in westerly shear are anticipated to bring about weakening. Most of the guidance suggests Erin will degenerate into a tropical wave late in the period, which is certainly a possibility. However, the GFS suggests that the vertical shear may start to decrease beyond 72 hours, albeit still remaining somewhat zonal. If this were to occur, Erin may have the opportunity to restrengthen at longer ranges, but it would also have to deal with a much drier airmass to the west, which even a small amount of westerly shear could help fling into the inner core. I will be conservative and hold the intensity steady state later in the period, but this forecast is of little confidence.

Erin is moving west-northwest to the south of a weak mid-level ridge caused by an upper tropospheric cold low near the Azores. The models are in good agreement on sending Erin on this general trajectory for the next 48-72 hours. After that time, there is some discrepancy in how far west Erin moves at longer ranges. In general, the guidance has continued to trend northward with the most recent cycle, and my forecast will follow that, although it is still well to the south of the multi-model consensus, and similar to the 0300Z NHC prediction. I am having a tough time biting on full on recurvature, as UW-CIMSS steering data suggests that the low-level ridge remains strong, and is not being significantly affected by any large-scale cyclonic circulations; in addition, I feel the upper low is too far north of Erin to cause an appreciable poleward bend to the track at longer ranges, as long as the cyclone remains weak. If Erin strengthens more than forecast, recurvature is a viable possibility.

Intensity forecast and positions

INITIAL 08/16 0300Z 15.5°N 29.1°W 35 KT 40 MPH
12 hour 08/16 1200Z 16.3°N 31.5°W 40 KT 45 MPH
24 hour 08/17 0000Z 17.6°N 33.8°W 45 KT 50 MPH
36 hour 08/17 1200Z 18.8°N 36.7°W 45 KT 50 MPH
48 hour 08/18 0000Z 19.9°N 39.6°W 45 KT 50 MPH
72 hour 08/19 0000Z 20.9°N 42.9°W 40 KT 45 MPH
96 hour 08/20 0000Z 21.6°N 46.5°W 40 KT 45 MPH
120 hour 08/21 0000Z 22.5°N 50.4°W 40 KT 45 MPH

Track forecast



Figure 2. My forecast track for Erin.



Invest 92L

An area of low pressure near or over the Yucatan Peninsula is producing a large area of disorganized cloudiness and thunderstorms over the southern Gulf of Mexico and the western Caribbean Sea.



Figure 3. Latest infrared satellite image of Invest 92L. Image credit: NOAA's Satellite Services Division (SSD).

Surface observations from Campeche, on the west shore of the Yucatan Peninsula, has shown a tendency toward southwest winds over the last hour, while winds at Merida, located on the north shore of the peninsula, has been reporting southeast winds. This suggests there is still some decent vorticity remaining with 92L despite its current internal struggles, and as long as that remains the case, it needs to be monitored. Interestingly, recent satellite analyses suggest that the low-level center of 92L has recently emerged into the Gulf of Mexico proper off the northwest coast of the Yucatan, but this would be well to the north and west of the current official center fix.

Water vapor imagery shows a small upper low north of the Yucatan Peninsula diving southwestward toward what I perceive to be the center, which could temporarily increase the shear over the storm. On the other hand, the GFS shows this low weakening and moving southward, and that is supported by recent trends in UW-CIMSS 200 mb vorticity data, and also, to an extent, on water vapor imagery. Should this verify, the upper flow pattern over the Gulf would become more favorable for tropical cyclogenesis before the system hits the monstrous shear well north of about 25 or 26N, at which point development would likely be stifled.

Overall, I am still not convinced the environment over the Gulf will completely inhibit 92L's chances of becoming a tropical cyclone, and we need to monitor this system carefully today. A reconnaissance aircraft is scheduled to investigate the disturbance later today, if necessary, although that will not happen if convection does not redevelop.

The models have made a significant westward shift over the last couple cycles, with the latest runs of the GFDL and CMC now showing a landfall in southeast and central Texas, respectively; additionally, the 0z Euro has also shifted from a central Louisiana landfall to a southern Mexico landfall. The Mexico landfall is still a possibility if 92L does not gain a definite poleward component of motion today. Synoptic steering data indicates that the ridge over the southwestern United States has moved eastward a little over the last several hours, which could explain the recent model shifts and lend them some credibility. On the other hand, the GFS still shows a landfall in southeastern Louisiana in about 54 hours. Given the shifts, I will move a little westward as well, but only to about Houma, Louisiana until I see more convincing evidence that a large westward turn is going to occur.

It should be noted that, in general, the guidance has trended toward the system having more time over water; this would be especially true if it took the more western track. If that were to verify, the GFS shows the shear wall over the northern Gulf Coast gradually relaxing, which would be more supportive of intensification.

Regardless of development, I still anticipate that most of the winds and rain will be to the east of the center due to westerly shear, and the landfall location will be of little consequence unless the upper air pattern changes.

Interests in the western and northern Gulf Coasts should monitor the progress of this disturbance.

Probability of development in 48 hours: 50%

Tropical Storm Erin Invest 92L

Updated: 8:39 AM GMT on August 16, 2013

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Tropical weather analysis - August 15, 2013

By: KoritheMan, 6:10 AM GMT on August 15, 2013

Tropical Depression Five

Tropical Depression Five formed over the eastern Atlantic near the Cape Verde Islands late Wednesday. As of the latest NHC intermediate advisory, the following information was available on the cyclone:

Wind: 35 mph, with higher gusts
Location: 14.2°N 24.2°W
Movement: WNW at 14 mph
Pressure: 1008 mb

The intensity of the tropical cyclone is a little difficult to estimate this evening. On one hand, 0z Dvorak numbers from TAFB and SAB were only at 1.0, the very bottom of the scale, but an ASCAT pass near 0z showed winds near tropical storm force to the east of the center. In addition, the satellite presentation is impressive, with the center presumed to be located along the eastern portion of the deep convection.



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

I presume the depression is near tropical storm strength, but even if it's not quite there yet, environmental conditions appear favorable for a steady intensification until around 48 hours, when the SHIPS model and objective SST analyses suggest that the depression will encounter cooler water, and consequently, a slightly more stable airmass. None of the guidance suggests significant strengthening over the next few days, and the GFS shows westerly shear increasing in about 72 hours due to a developing cold low over the central Atlantic. The depression is expected to move into warmer waters late in the period, which may offset the potential for westerly shear, and allow for at least a steady state storm. I have memories of Dorian, which also struggled in this same area, however, so it will be most interesting to monitor future intensity trends. It is possible that the cyclone strengthens a little more than forecast in the short-term. It should also be noted that conditions may become more favorable beyond day five, with a considerable decrease in vertical shear.

The depression is moving steadily west-northwest, to the south of a weak mid-level ridge. An upper low over the northeastern Atlantic is maintaining a sizable weakness to the north of the tropical cyclone. However, this feature is forecast to gradually retreat northward over the next few days, and the cyclone is expected to respond by turning westward at longer ranges. The guidance remains in a decent agreement on the synoptic pattern for a system still in its formative stage, and my forecast track is similar to, but a little south of, the latest NHC prediction.

It is too early to speculate whether or not the depression will recurve out to sea as most Cape Verde cyclones do, or if it will continue westward and potentially threaten land at extended ranges. My best guess right now, based on the pattern, is that the system still stands a chance at recurving, but that the odds are currently against it doing so. We will have to monitor future trends carefully.

Because of the close proximity to the Cape Verde Islands, a tropical storm warning has been issued for a portion of that archipelago.


Intensity forecast and positions

INITIAL 08/15 0300Z 14.0°N 23.5°W 30 KT 35 MPH
12 hour 08/15 1200Z 14.3°N 25.0°W 35 KT 40 MPH
24 hour 08/16 0000Z 14.5°N 27.5°W 40 KT 45 MPH
36 hour 08/16 1200Z 15.1°N 31.8°W 45 KT 50 MPH
48 hour 08/17 0000Z 15.7°N 35.0°W 50 KT 60 MPH
72 hour 08/18 0000Z 16.4°N 38.5°W 45 KT 50 MPH
96 hour 08/19 0000Z 16.8°N 42.0°W 45 KT 50 MPH
120 hour 08/20 0000Z 16.9°N 46.1°W 45 KT 50 MPH

Track forecast



Figure 2. My forecast track for Tropical Depression Five.

NHC storm information

000
WTNT35 KNHC 150541
TCPAT5

BULLETIN
TROPICAL DEPRESSION FIVE INTERMEDIATE ADVISORY NUMBER 1A
NWS NATIONAL HURRICANE CENTER MIAMI FL AL052013
200 AM AST THU AUG 15 2013

...CENTER OF THE DEPRESSION PASSING SOUTH OF THE CAPE VERDE
ISLANDS...


SUMMARY OF 200 AM AST...0600 UTC...INFORMATION
----------------------------------------------
LOCATION...14.2N 24.2W
ABOUT 55 MI...90 KM SSE OF FOGO IN THE CAPE VERDE ISLANDS
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...WNW OR 290 DEGREES AT 14 MPH...22 KM/H
MINIMUM CENTRAL PRESSURE...1008 MB...29.77 INCHES


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

NONE.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* THE SOUTHERN CAPE VERDE ISLANDS OF MAIO...SANTIAGO...FOGO...AND
BRAVA

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

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


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 200 AM AST...0600 UTC...THE CENTER OF TROPICAL DEPRESSION FIVE
WAS LOCATED NEAR LATITUDE 14.2 NORTH...LONGITUDE 24.2 WEST. THE
DEPRESSION IS MOVING TOWARD THE WEST-NORTHWEST NEAR 14 MPH...22
KM/H...AND THIS GENERAL MOTION IS EXPECTED TO CONTINUE DURING THE
NEXT COUPLE OF DAYS. ON THE FORECAST TRACK...THE CENTER OF THE
CYCLONE SHOULD MOVE TO THE SOUTH AND SOUTHWEST OF THE SOUTHERN CAPE
VERDE ISLANDS TODAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 35 MPH...55 KM/H...WITH HIGHER
GUSTS. SOME STRENGTHENING IS FORECAST DURING THE NEXT 48 HOURS...
AND THE DEPRESSION IS EXPECTED TO BECOME A TROPICAL STORM LATER
TODAY.

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


HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM CONDITIONS ARE EXPECTED OVER THE SOUTHERN CAPE
VERDE ISLANDS TODAY. STRONGER WINDS ARE LIKELY IN AREAS OF HIGHER
TERRAIN ON THE ISLANDS.

RAINFALL...TROPICAL DEPRESSION FIVE IS EXPECTED TO PRODUCE TOTAL
RAIN ACCUMULATIONS OF 2 TO 4 INCHES OVER THE SOUTHERN PORTION OF
THE CAPE VERDE ISLANDS.


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

$$
FORECASTER BEVEN



Invest 92L

An area of low pressure, associated with a tropical wave, is located over the western Caribbean Sea about 150 miles east of Chetumal, Mexico. I am not impressed by the organization with this system, with a recent ASCAT pass and a couple of buoy observations suggesting that the wave axis is not well-defined. In addition, convection has essentially evaporated over the last several hours, which suggests that 92L is not self-sustaining, losing its convection during diurnal minimum.



Figure 3. Latest infrared satellite image of Invest 92L. Image credit: NOAA's Satellite Services Division (SSD).

Despite the recent downward trend in convection, atmospheric conditions still appear favorable for the formation of a tropical depression over the western Caribbean or southern Gulf of Mexico, although if this occurs, it is likely to be in the Gulf, since 92L is progressing steadily west-northwestward toward Yucatan. I should note that the intensity forecast for this system is rather tricky; there is little shear over the southern Gulf, but the shear vector there is northerly, which is not a favorable combination for a northward-moving system. On the other hand, upper-level winds are favorable where the low is currently at, but again, due to time constraints, 92L is unlikely to become a tropical cyclone prior to crossing Yucatan within the next 12-18 hours. Also, the GFS still shows westerly shear increasing markedly north of 25N over the Gulf, so while the system may try to develop some in the southern Gulf, my current thinking is that this may no longer happen, primarily because the circulation is still not closed.

Regardless of development, heavy rainfall and gusty winds will accompany this system over portions of the Yucatan Peninsula and Belize; this weather will eventually spread up to the northern Gulf Coast.

My favored landfall point right now is southeastern Louisiana near Grand Isle in about 72 hours, although water vapor imagery shows the Texas ridge building eastward into central Louisiana, so it is possible this could be too far west if this trend persists.

It's also worth noting that, regardless of whether the system becomes a tropical cyclone, the primary band of weather will be found to the east of the center due to shear, making the landfall point of little consequence.

Probability of development in 48 hours: 50%

2013 Atlantic hurricane season Tropical Depression Five Invest 92L

Updated: 6:18 AM GMT on August 15, 2013

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Tropical weather analysis - August 13, 2013

By: KoritheMan, 3:24 AM GMT on August 14, 2013

Utor

Dangerous Typhoon Utor is closing in on southwestern China, with a landfall likely to occur near Zhanjiang Wednesday evening local time. As of the just released 0300Z JTWC advisory, the following information was available on the typhoon:

Wind: 100 mph, with higher gusts
Location: 20.7°N 112.1°E
Movement: NW at 13 mph
Category: 2 (Saffir-Simpson Hurricane Wind Scale)

Satellite images suggest a deterioration of the cloud pattern, with deep convection limited primarily to the southern semicircle. A recent SSMIS microwave pass suggests that the eye is open to the north; in addition, the mid-level center appears to be displaced a little to the west of the low-level center, suggesting an increase in easterly shear. Satellite estimates have decreased, and Utor was assigned an 85 kt operational intensity by the JTWC at 0300Z, which is down 10 kt from the 95 kt operational assessment by the agency at 2100Z.



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

In addition to the shear, Utor has moved well beyond the area of highest heat content; given this and the structure, it is entirely possible that Utor will weaken a little more prior to landfall, but my forecast essentially keeps it steady state until it moves inland. After landfall, the cyclone will probably decay quite rapidly over the high terrain of southwestern China, losing its identity in about 72 hours.

Water vapor imagery shows an amplified mid- to upper-level trough over central China, which is helping to create and amplify a weakness in the subtropical ridge to the north of the typhoon. The weakness created by this trough shows up rather nicely on the latest UW-CIMSS steering charts. My forecast track is very similar to the 0300Z JTWC forecast track, taking Utor inland within 8-12 hours. After landfall, the cyclone is expected to shear apart and turn more toward the west or possibly south of west as a low-level ridge builds in to the north of the typhoon. There has been no change in the track philosophy or reasoning, and the steering pattern in front of the typhoon appears very well-defined.

Intensity forecast

INITIAL 08/14 0300Z 95 KT 100 MPH
12 hour 08/14 1200Z 80 KT 90 MPH...INLAND
24 hour 08/15 0000Z 50 KT 60 MPH...INLAND
36 hour 08/15 0600Z 30 KT 35 MPH...INLAND
48 hour 08/16 0000Z 25 KT 30 MPH...INLAND
72 hour 08/17 0000Z...DISSIPATED



Invest 92L

A westward-moving tropical wave over the western Caribbean Sea is producing a large area of showers and thunderstorms. This system was labeled "Invest 92L" earlier today by the National Hurricane Center. This large disturbance remains disorganized, with little evidence of concentrated convection. Additionally, there appears to be a couple of competing circulations within the broad cyclonic gyre composing this wave.



Figure 2. Latest infrared satellite image of Invest 92L. Image credit: NOAA's Satellite Services Division (SSD).

After careful analysis of satellite imagery this evening, I can make out a center near the Nicaragua/Honduras border moving west, with another distinct mid-level center to the southwest of Jamaica. UW-CIMSS 850 mb vorticity data is in conflict, suggesting the mid-level center near Jamaica is considerably weaker, while also place the mid-level center near Honduras/Nicaragua farther to the south than it actually is. Given the dichotomies, it is difficult to identify which of the centers is stronger. I don't really have much reason to favor one over the other in this particular instance, except noting that the area near Jamaica has a little more convection. Interestingly, UW-CIMSS analyzed a developing anticyclone over the Honduras/Nicaragua mid-level center, which could signify that the system might try to get going in that region. NOAA buoy 42057, located about 180 miles west-southwest of Negril, Jamaica, showed a drop in pressure earlier that was outside of the normal diurnal ranges; this could suggest that the wave axis was near this location earlier, especially given the magnitude of such a pressure drop. The conflicting signals indicate that 92L remains disorganized, and the large size of the circulation associated with this disturbance will probably not allow for rapid development.

The GFS continues to want to bring this system up toward the northern Gulf Coast area in less than four days, which seem awfully fast to me. It appears that, ultimately, the track of 92L will depend largely on where a definite center decides to consolidate; should it develop farther westward near the Nicaragua/Honduras border, 92L would likely take a more western path into the Bay of Campeche, where it could continue west into Mexico, or slow down considerably and eventually move north through the weakness connected with the eastern United States trough. It is difficult to tell which option is the most viable right now, and there has been some model support for a more westward solution as well, with the 12z ECMWF actually showing the 850 mb vorticity maximum moving west toward central Mexico. Regardless of which path the system decides to take, upper-level winds do not appear conducive to the formation of a hurricane, with some southwesterly shear over the southern Gulf of Mexico associated with the upper-level trough. If the system can organize a little quicker while still in the Caribbean, we would likely be dealing with a somewhat stronger system.

Probability of development in 48 hours: 30%



Invest 93L

A tropical wave off the west coast of Africa ("93L") is producing an area of showers and thunderstorms. Environmental conditions appear favorable for gradual development of this disturbance over the next couple of days. However, the GFS shows westerly shear increasing in about 72 hours, which could inhibit development if the system tracks farther to the north; if it can stay south of 20N, it may have a better chance at surviving, although the upper-level wind pattern will still be less than ideal.



Figure 3. Latest infrared satellite image of Invest 93L. Image credit: NOAA's Satellite Services Division (SSD).

It is too early to determine whether or not 93L recurves like many Cape Verde systems do, or if it maintains a more westward track and potentially threatens land. There is a weakness to the north of the system associated with a mid- to upper-level trough, but this weakness appears to be small and fragile. While possible, I don't feel that 93L will track all the way up to 20N. I do, however, anticipate a turn toward the west-northwest over the next few days, with a turn toward the west by day four or five as the the trough lifts out and mid-level ridging builds in behind it.


Probability of development in 48 hours: 20%

2013 Pacific typhoon season Typhoon Utor Invest 92L Invest 93L

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Tropical weather analysis - August 11, 2013

By: KoritheMan, 8:00 AM GMT on August 11, 2013

Utor

Dangerous Typhoon Utor is heading for a direct hit on central Luzon in the Philippines. As of the 0300Z JTWC advisory, the following information was available on the typhoon:

Wind: 115 mph, with higher gusts
Location: 14.4°N 125.9°E
Movement: W at 13 mph
Category: 3 (Saffir-Simpson Hurricane Wind Scale)

The satellite presentation of Utor is rather spectacular this morning, with numerous well-defined rainbands to the west and north of the small eye, with more broken bands extending elsewhere throughout the circulation. Satellite estimates have risen considerably ever since the eye became apparent in conventional satellite imagery around 0400 UTC, with the latest the CIMSS Advanced Dvorak Technique (ADT) raw T number hovering at 7.4, or near 155 kt (180 mph) on the Dvorak classification system. Final T numbers from the agency are lower, at 5.6 as of 0700 UTC, although I anticipate that Utor is a stronger system. Convection in the eyewall continues to increase, and the upper-tropopspheric outflow signature is exceptionally well-defined. This is one instance I wish I had a reconnaissance aircraft. The latest JTWC estimate puts Utor at 115 kt, and that was used in the initial intensity below to supersede the operational assessment at 0300Z.



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

Since I see no signs of a concentric eyewall cycle in satellite, radar or microwave data, I have a distinct feeling Utor is undergoing rapid intensification. Under this premise, my forecast brings the cyclone to super typhoon status at the time of landfall, which is forecast to occur on central Luzon in about 18 hours; it is possible that Utor could briefly reach Category 5 status prior to landfall. After landfall, the typhoon is forecast to weaken, following the typical progression of inland-progressing tropical cyclones. Once the cyclone emerges into the South China Sea in about 36 hours, environmental conditions are forecast to remain favorable for reintensification; however, water vapor imagery and UW-CIMSS wind shear data show about 20 kt of southwesterly shear near longitude 115E, which the GFS suggests could increase over the typhoon as it approaches mainland China; in addition, oceanic heat content decreases rather sharply west of 115E, which could also offset rapid intensification. Some reintensification to major hurricane status is shown prior to Utor's second landfall, but it's simply not possible to determine how strongly the vertical shear or lower heat content might affect the cyclone at this point.

Utor remains pretty much on track, and appears to be moving between west and west-northwest under a strong ridge to the north. Water vapor imagery shows a slow-moving shortwave trough over central China that the global models suggest will slowly erode the western portion of the ridge to the north of Utor. As a consequence, I show the typhoon turning northwest in about 36 hours, gravitating toward that weakness. That general northwest motion is forecast to continue after landfall. Although Utor is currently forecast to remain well to the west of Hong Kong, interests there should closely follow the progress of the typhoon after it emerges into the South China Sea; they are still well within the cone of uncertainty from the JTWC, and they will be on the more dangerous side of the typhoon regardless.

Significant flooding and mudslides will likely accompany Utor and affect a large portion of Luzon; n addition, sustained winds between 125 and 160 mph will likely accompany the eye near and to the north of where the center crosses the coast. However, Utor is a relatively small typhoon, so the core of strongest winds will likely be confined to a few mile area near the eye.

Intensity forecast

INITIAL 08/11 0600Z 115 KT 135 MPH
12 hour 08/11 1800Z 130 KT 150 MPH...APPROACHING NORTHERN LUZON
24 hour 08/12 0600Z 100 KT 115 MPH...INLAND
36 hour 08/12 1800Z 95 KT 110 MPH...OVER SOUTH CHINA SEA
48 hour 08/13 0600Z 100 KT 115 MPH
72 hour 08/14 0600Z 100 KT 115 MPH...AT THE COAST OF SOUTHWESTERN CHINA
96 hour 08/15 0600Z 60 KT 70 MPH...INLAND
120 hour 08/16 0600Z 25 KT 30 MPH...INLAND

Track forecast



Figure 2. My forecast track for Utor.

2013 Pacific typhoon season Typhoon Utor

Updated: 8:09 AM GMT on August 11, 2013

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Tropical weather analysis - August 9, 2013

By: KoritheMan, 5:43 AM GMT on August 09, 2013

Henriette

Henriette unexpectedly peaked as a 90 kt Category 2 hurricane on Thursday afternoon, but has begun the long anticipated weakening trend. As of the 0300Z NHC official advisory, the following information was available on the cyclone:

Wind: 100 mph, with higher gusts
Location: 17.0°N 140.4°W
Movement: W at 12 mph
Pressure: 981 mb
Category: 2 (Saffir-Simpson Hurricane Wind Scale)

Satellite images suggest a significant degradation of the cloud pattern over the last several hours, with the small eye that was distinct and surrounded by cold cloud tops now hiding in the convection, which in itself has become a bit elongated. There was no evidence of an eye on recent microwave data, and recent satellite images suggest possible dry air entrainment. 0z satellite estimates still supported at least a low-end Category 2 hurricane, but it will be interesting to see the 6z estimates, which will be out soon.



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

With the help of a couple timely microwave passes, it appears that Henriette has begun to turn to the west-southwest, which would be consistent with UW-CIMSS steering for a hurricane of this intensity. With the ridge expected to build westward with Henriette over the next several days, the synoptic pattern appears to be of little question. Overall, the model consensus has barely budged, and my forecast track is similar to the one from the National Hurricane Center, taking the hurricane well south of the Hawaiian Islands over the next couple of days.

Henriette will be moving into progressively warmer waters throughout the forecast period, which would normally favor intensification. On the flip side, however, water vapor imagery shows westerlies west of 150W, which Henriette is forecast to encounter in about three days. That, combined with a relatively stable airmass suggests that the hurricane should continue to steadily weaken, and my intensity forecast scheme is identical to the 0300Z NHC prediction. It is possible that Henriette could weaken a little faster than indicated below, particularly if current storm trends persist.

Intensity forecast and positions

INITIAL 08/07 0300Z 17.0°N 140.4°W 85 KT 100 MPH
12 hour 08/07 1200Z 16.7°N 142.1°W 80 KT 90 MPH
24 hour 08/08 0000Z 16.3°N 144.7°W 70 KT 80 MPH
36 hour 08/08 1200Z 15.7°N 147.2°W 60 KT 70 MPH
48 hour 08/09 0000Z 15.0°N 150.0°W 50 KT 60 MPH
72 hour 08/10 0000Z 13.6°N 156.1°W 35 KT 40 MPH

Track forecast



Figure 2. My forecast track for Henriette. I cannot draw forecast points beyond three days, again due to the limitations of the map I use.


Invest 92E

An area of low pressure located about 700 miles southwest of Manzanillo remains disorganized. The circulation appears to be not well-defined, and the shower activity is of a pulsating nature, lacking significant organization or persistence.



Figure 3. Latest infrared satellite image of Invest 92E. Image credit: NOAA's Satellite Services Division (SSD).

However, upper-level winds are forecast to improve over the next couple of days, and the system could become a tropical depression in a few days. One limiting factor that we'll need to watch for is the system still being embedded in the monsoon trough, which is a situation not generally considered conducive for tropical cyclone development.

The system is forecast to move westward over the next few days.

Probability of development in 48 hours: 50%



Invest 93E

Albeit not updated since the coordinates 1800Z, a secondary area of low pressure, located about 1600 miles southwest of the southern tip of Baja California was designated "Invest 93E" earlier on Thursday. Like its predecessor, this system is trapped in the monsoon trough, and is having trouble focusing adequate surface convergence and upward motion; there also appears to be a little bit of northeasterly shear over the area.

The system is forecast to move slowly westward over the next couple of days, and the GFS shows upper-level winds relaxing very slowly, particularly beyond 72 hours.

I do not expect significant development of this disturbance over the next several days, although it may attempt to do so later on as it edges closer to the central Pacific basin.

Probability of development in 48 hours: 20%



Gulf of Mexico development possible in a little over a week

While none of the global models explicitly show tropical cyclogenesis right now, there has been some indication from the operational GFS over the last couple runs that a broad area of low pressure will form over the Yucatan Peninsula/Bay of Campeche region around the 180 hour timeframe. I am a little unsure of where this potential development comes from; yesterday I thought it was the tropical wave in the eastern Caribbean Sea that the National Hurricane Center has stopped mentioning in their routine Tropical Weather Outlooks. Upon further examination today, however, I have come to the conclusion that perhaps the catalyst for this hypothetical storm is the tropical wave moving into the central Atlantic around 35W, which makes sense given the modeled timeframe.

There has also been some ensemble support from the GFS and CMC for lowering pressures across the region during that general timeframe, and the GFS does show upper-level winds improving in the northwestern Caribbean Sea/southern Gulf of Mexico region during that time. This is a situation that will have to be watched carefully over the next week and beyond.

The future track of any such system is still highly uncertain, which is to be expected with long-range forecasts. Based on the pattern I see in the models *now* (which again, can and probably will change), the most likely target areas for such a system will likely be the western Gulf Coast from Mexico to Texas, or the Florida peninsula region, as the models show a trough along the east coast leaving a weakness in the eastern Gulf. But again, we will have a better idea of the track of this potential system as we get farther out in time, most likely when the system reaches the western Caribbean in about a week.

The 0z GFS shows several weak tropical cyclones developing over the next two weeks. While this is long-range and should be taken with a healthy degree of skepticism, two of these modeled cyclones develop before the 220 hour mark, when the model suffers from resolution issues. Although it is likely that these systems are ghost storms and will be dropped in subsequent runs, there have been periodic hints within the models, particularly the GFS, that conditions in the Atlantic are beginning to become more favorable for tropical cyclone formation. I suspect the models will continue to periodically show development as they respond to these more favorable conditions, including a northward-migration of the ITCZ and lower vertical wind shear values in the Caribbean.

I do anticipate things to get active, and by this time next month, I'd wager that we will scarcely remember the current lull.

2013 Atlantic hurricane season 2013 Pacific hurricane season Hurricane Henriette Invest 92E Invest 93E

Updated: 5:47 AM GMT on August 09, 2013

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Tropical weather analysis - August 8, 2013

By: KoritheMan, 5:53 AM GMT on August 08, 2013

Henriette

Henriette continues as a hurricane as of the 0300Z NHC advisory:

Wind: 85 mph, with higher gusts
Location: 17.0°N 136.5°W
Movement: WNW at 10 mph
Pressure: 984 mb
Category: 1 (Saffir-Simpson Hurricane Wind Scale)

There has been no appreciable change to the cloud pattern or organization of the hurricane over the last several hours; the eye has been faintly visible on conventional satellite images, but the eyewall convection is not as intense as it was earlier, particularly in the northern semicircle, suggesting a possible intrusion of dry air in that direction. In addition, UW-CIMSS diagnoses about 15 kt of westerly shear over the hurricane. Satellite estimates remain supportive of an intensity of 75 kt for now, although it is anticipated that Henriette will weaken soon.



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

The hurricane has likely crossed the 26C isotherm, with the SHIPS model showing underlying sea surface temperatures decreasing even further over the next day or two. Thereafter, waters warm along the projected track, but the GFS suggests an increase in westerly shear, with Henriette losing its anticyclone. Lacking upper support, the warmer waters are not expected to allow reintensification at longer ranges, and a gradual decay, down to a remnant low, is shown at day four.

The subtropical ridge is rebuilding to the north of Henriette as large-scale zonal flow develops to the north of the hurricane. This was well-advertised by the global models over the last few days, and the pattern appears to be very stable. The hurricane is expected to turn toward the west-southwest over the next 24-48 hours, and that general motion is anticipated to continue throughout the forecast period. The model consensus continues to be in remarkable agreement on the path of the hurricane, showing Henriette passing well to the south of the Hawaiian Islands. The ECMWF and GFS have come into better agreement on the track, further increasing confidence in it.

Intensity forecast and positions

INITIAL 08/08 0300Z 17.0°N 136.5°W 75 KT 85 MPH
12 hour 08/08 1200Z 17.3°N 137.7°W 70 KT 80 MPH
24 hour 08/09 0000Z 17.3°N 139.6°W 65 KT 75 MPH
36 hour 08/09 1200Z 16.9°N 141.3°W 55 KT 65 MPH
48 hour 08/10 0000Z 16.5°N 144.1°W 50 KT 60 MPH
72 hour 08/11 0000Z 15.5°N 149.7°W 40 KT 45 MPH
96 hour 08/12 0000Z 13.9°N 156.7°W 30 KT 35 MPH...POST-TROPICAL/REMNANT LOW

Track forecast



Figure 2. My forecast track for Henriette. I can't provide a five-day forecast point because of the limitations of the map I use.



Invest 92E

An area of low pressure has developed several hundred miles southwest of Acapulco, Mexico. The associated shower activity is currently disorganized, but upper-level winds are forecast to become more conducive to development, with the current moderate northeasterly shear transitioning to a lighter, more uniform easterly regime. The GFS suggests the environment will become anticyclonic in about 72 hours, which could favor significant intensification at that time. The GFS continues to develop this system into a tropical cyclone in a few days.

That model also suggests the possibility of another tropical cyclone moving in tandem with 92E, which, if true, could complicate the track and intensity in later periods. The pattern suggests this will be yet another system that enters the central Pacific, but it is too early to ascertain the possible threat to Hawaii.

Probability of development in 48 hours: 30%



Caribbean Sea tropical wave

A tropical wave moving through the eastern Caribbean Sea is located about 150 miles north of the northern coast of Venezuela. Satellite imagery suggests the associated shower activity is limited due to dry air and westerly shear. The GFS suggests the upper flow will remain unfavorable for development across the Caribbean for at least the next five days. Thereafter, when the system approaches the western Caribbean, upper-level winds could begin to improve, and the overall environment could begin to moisten. This combination could result in the formation of a broad area of low pressure. None of the models currently show development, with the exception of the experimental FIM model, which runs off the GFS algorithm. Since I have no verification for this model, I am not counting it as reliable. It is possible the models will latch onto development with time, and we will have to watch this feature to see how it evolves.

The current steering layer forecasts indicates that this system will likely pose a threat to the western Gulf Coast if it makes it into the Gulf proper. An alternate scenario is that the wave does not develop and moves across Central America into the Pacific, where it would need to be monitored for development in that basin.

In the meantime, vorticity is lacking, with CIMSS analysis showing very little cyclonic signature above 850 mb. It is possible that convection will increase during the next couple of days as the wave transits the Caribbean; it is located near the mid-oceanic trough, and the associated southwesterly mid- to upper-level flow connected with that feature could provide an environment of upper diffluence over the system, albeit accompanied by shear. An increase in convection could result in stronger vorticity values being noted above 850 mb, which could ultimately increase its chances of development.

Probability of development in 48 hours: 10%

2013 Atlantic hurricane season 2013 Pacific hurricane season Hurricane Henriette Invest 92E

Updated: 6:05 AM GMT on August 08, 2013

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Tropical weather analysis - August 6, 2013

By: KoritheMan, 3:10 AM GMT on August 07, 2013

Henriette

Hurricane Henriette continues to churn in the tropical Pacific:

Wind: 90 mph, with higher gusts
Location: 15.1°N 133.1°W
Movement: WNW at 10 mph
Pressure: 981 mb

The satellite presentation of the hurricane hasn't changed appreciably since the 2100Z advisory from the National Hurricane Center, and satellite estimates from TAFB and SAB still support an 80 kt hurricane.



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

Recent microwave data suggest little change to the inner core structure of Henriette; a recent AMSUB pass just before 0z did not show much evidence of an eye, but that instrument tends to not detect such features unless the hurricane is particularly well-defined, at least in my experience. The intensity guidance suggests little change over the next 12 hours, although there is some potential for very slight strengthening while Henriette remains over warm water. Beyond that time, the hurricane is forecast to approach cooler water and an increasingly more stable airmass, which is expected to lead to a weakening of the cyclone. My forecast is a little higher than the National Hurricane Center forecast, and keeps Henriette a minimal tropical storm at the end of the forecast period, since the hurricane is forecast to remain over water at least in the lower range of 26C throughout most of the forecast period; in fact, waters may even warm the closer the system gets to the Hawaiian Islands.

Henriette is still moving through a weakness in the subtropical ridge extending westward to just west of 135W. As Henriette rounds the closing of this weakness, a more pronounced turn to the west-northwest is anticipated as the subtropical ridge reamplifies to the north of the hurricane. Near the end of the period, a turn to the west-southwest is expected as Henriette weakens and becomes a shallower system. The global models remain in good agreement on the track, although the ECMWF is along the northern edge of the guidance envelope, while the GFS lies along the southern edge of the guidance. My forecast is a blend of both but somewhat favoring the ECMWF, as I feel Henriette will be a little stronger at later time periods. While interests in the Hawaiian Islands should continue to monitor the progress of Henriette, confidence is increasing that the hurricane will pass well to the south of the archipelago, although it may come close enough to generate locally heavy surf on windward-facing beaches early next week.

The coordinates and track map given below are based on the 2100Z advisory. The 0300Z advisory has come out since then, but I was writing this blog while the former advisory was still active. Deal with it.

Intensity forecast and positions

INITIAL 08/06 2100Z 14.7°N 132.3°W 80 KT 90 MPH
12 hour 08/07 0600Z 15.8°N 133.7°W 80 KT 90 MPH
24 hour 08/07 1800Z 17.2°N 135.2°W 75 KT 85 MPH
36 hour 08/08 0600Z 17.5°N 137.9°W 65 KT 75 MPH
48 hour 08/08 1800Z 17.7°N 140.0°W 60 KT 70 MPH
72 hour 08/09 1800Z 17.8°N 144.8°W 45 KT 50 MPH
96 hour 08/10 1800Z 17.0°N 150.0°W 40 KT 45 MPH
120 hour 08/11 1800Z 15.5°N 157.1°W 35 KT 40 MPH

Track forecast



Figure 2. My forecast track for Henriette.



Elsewhere

An area of low pressure is expected to form offshore the south coast of Mexico in the next few days. The GFS shows this feature eventually becoming a tropical cyclone.

The Atlantic remains quiet for now, although the GFS continues to significantly lower the wind shear over the Caribbean, which is something we have not seen much of this year. This is forecast to happen in as little as a week, which is well before the model suffers from resolution issues. The shear is forecast to decrease even more in the two week timeframe, and I imagine the models will respond to this pattern by forecasting development.

Things will wake up in the Atlantic soon enough.

2013 Pacific hurricane season Hurricane Henriette

Updated: 3:13 AM GMT on August 07, 2013

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Tropical weather analysis - August 6, 2013

By: KoritheMan, 7:48 AM GMT on August 06, 2013

Gil

Gil stubbornly maintains the status quo as of the 0300Z NHC advisory:

Wind: 35 mph, with higher gusts
Location: 13.4°N 140.2°W
Movement: W at 9 mph
Pressure: 1006 mb

Due to the lack of satisfactory microwave passes over the last several hours, the center of Gil is rather difficult to locate, but I presume it is embedded within the deep convection, which is now exhibiting banding features. There is still some easterly shear over the system, but it appears to be lessening. Satellite estimates have come up, with the 6z estimate from SAB climbing from 1.5 to 2.0. TAFB has yet to release their numbers, but it is probable that Gil is a tropical storm again.



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

Since the shear appears to be lessening, the environment ahead of Gil looks favorable for additional intensification. The statistical models have trended a bit more aggressive with this cycle, with the LGEM taking Gil up to hurricane strength again in about five days. The more southerly itinerary will allow for the cyclone to remain over warm waters throughout the forecast period, perhaps obliterating its enemies and raking in some additional Gil. My forecast is close to but a little below the LGEM model, and is well above the global models, which mysteriously do not show much reintensification.

The initial motion of Gil has also been hard to determine, particularly because I feel the center is embedded in the cold cloud tops. However, there are indications from shortwave infrared satellite imagery that the low-level center may be a little farther east than the estimate provided by the National Hurricane Center earlier, which I reflect in my 6z position below. The tropical storm is forecast to move westward for the next 48 hours, followed by a turn toward the west-northwest as it rounds a weakness in the subtropical ridge associated with a digging upper trough off the coast of Alaska. The guidance remains in good agreement on the overall track, so confidence is high. My forecast track is a fair bit northward of where the NHC's is, primarily because I feel Gil will not weaken appreciably.

Intensity forecast and positions

INITIAL 08/06 0600Z 13.3°N 140.3°W 30 KT 35 MPH
12 hour 08/06 1800Z 13.3°N 141.4°W 35 KT 40 MPH
24 hour 08/07 0600Z 13.3°N 142.6°W 40 KT 45 MPH
36 hour 08/07 1800Z 13.5°N 143.8°W 45 KT 50 MPH
48 hour 08/08 0600Z 13.8°N 145.0°W 50 KT 60 MPH
72 hour 08/09 0600Z 14.7°N 148.0°W 55 KT 65 MPH
96 hour 08/10 0600Z 15.7°N 151.5°W 55 KT 65 MPH
120 hour 08/11 0600Z 16.8°N 156.1°W 50 KT 60 MPH

Track forecast



Figure 2. My forecast track for Gil.

Henriette

Tropical Storm Henriette continues to churn aimlessly in the eastern Pacific. As of the 0300Z advisory from the National Hurricane Center, the following information was available on the cyclone:

Wind: 70 mph, with higher gusts
Location: 13.5°N 130.0°W
Movement: NW at 12 mph
Pressure: 995 mb

According to the 6z ATCF file, Henriette is already a hurricane. The satellite signature is rather impressive, with a burst of cold convection and hints of a formative eyewall amidst the central dense overcast; a 0437Z SSMIS pass showed a low-level eye surrounded by deep convection, although the mid- to upper-level eye feature was displaced a little to the southwest of the low-level feature. Satellite estimates have continued to climb, and TAFB and SAB now suggest that Henriette is at the bottom of Category 1 strength.



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

Upper-level outflow continues to improve, particularly in the northern semicircle, which suggests that, while the aforementioned misalignment of the low- and mid-level eyes were due to northeasterly shear, the storm-relative vertical shear is lessening as forecast. Given this, Henriette still has potential to strengthen a little more during the next 24-36 hours, after which time the cyclone is forecast to cross the 26C isotherm and move into a somewhat more stable airmass. Waters are not forecast to cool below 25C throughout the forecast period, and they may even warm a little as Henriette gains latitude later in the period. My feeling is that some weakening will occur, as it always does in similar situations, but not as much as suggested by some of the guidance. Henriette is likely to be a tropical storm when it makes its closest approach to the Hawaiian Islands early next week, and interests there should continue monitoring the progress of this tropical cyclone.

Henriette is moving pretty much due northwest into an apparent break in the subtropical ridge extending westward to about 135W. As the cyclone nears that longitude, the global models show the ridge rebuilding, and the cyclone is expected to turn more toward the west-northwest during that time. The ECMWF continues to be along the southern edge of the global models, while the GFS lies along the northern edge. My forecast is biased toward the GFS is anticipation of a somewhat stronger system. If Henriette does not weaken as much as forecast late in the period, it may come significantly closer to Hawaii than currently forecast.

Intensity forecast and positions

INITIAL 08/06 0600Z 13.8°N 130.7°W 60 KT 70 MPH
12 hour 08/06 1800Z 14.8°N 132.1°W 65 KT 75 MPH
24 hour 08/07 0600Z 15.9°N 133.6°W 75 KT 85 MPH
36 hour 08/07 1800Z 17.2°N 135.1°W 75 KT 85 MPH
48 hour 08/08 0600Z 17.7°N 137.4°W 70 KT 80 MPH
72 hour 08/09 0600Z 18.3°N 141.4°W 60 KT 70 MPH
96 hour 08/10 0600Z 18.0°N 145.0°W 50 KT 60 MPH
120 hour 08/11 0600Z 18.1°N 155.4°W 45 KT 50 MPH

Track forecast



Figure 4. My forecast track for Henriette.

2013 Pacific hurricane season Tropical Depression Gil Tropical Storm Henriette

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Tropical weather analysis - August 5, 2013

By: KoritheMan, 6:05 AM GMT on August 05, 2013

Gil

Gil continues as a tropical depression as of the 0300Z NHC advisory:

Wind: 35 mph, with higher gusts
Location: 14.0°N 137.2°W
Movement: WSW at 8 mph
Pressure: 1007 mb

Gil miraculously managed to find a little more Gil within itself today, with a new burst of convection occurring to the southwest of the center. Satellite estimates suggest Gil is still a tropical depression, although the overall circulation appears to be on a slow decay trend, with a couple of scatterometer passes during the day on Sunday showing that the circulation had a little less definition.



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

While the GFS continues to indicate the environment will become more favorable in about three days, it is probable that Gil will not survive that long as a tropical cyclone, especially given the small size of the cyclone, which makes it more prone than usual to strong vertical shear. With continuing east-southeasterly shear and dry air, Gil is expected to continue to wind down, and I agree with the NHC intensity forecast scheme showing dissipation as a tropical cyclone within the next 12-24 hours. Because the waters are warm and the shear could lessen later in the period, I am keeping Gil as a distinct entity through the five-day forecast period. Although Gil may produce intermittent bursts of deep convection subsequent to dissipation, it is not currently expected that the storm will be able to regenerate amidst more favorable conditions later on, primarily because the small circulation is likely to be too disrupted. However, I will monitor the remnants for potential regeneration if shear decreases as forecast.

Satellite and microwave fixes indicate that Gil is moving toward the west-southwest, as has been expected over the last several days. In about 36-48 hours, the cyclone is expected to turn west as the ridge apparently flattens out a bit to the north of the system, which is likely to be a remnant low by that time. The guidance remains tightly clustered, and confidence in the overall forecast track is high.

Intensity forecast and positions

INITIAL 08/05 0300Z 14.0°N 137.2°W 30 KT 35 MPH
12 hour 08/05 1200Z 13.7°N 138.2°W 30 KT 35 MPH
24 hour 08/06 0000Z 13.5°N 139.6°W 30 KT 35 MPH...POST-TROPICAL/REMNANT LOW
36 hour 08/06 1200Z 13.3°N 140.8°W 30 KT 35 MPH...POST-TROPICAL/REMNANT LOW
48 hour 08/07 0000Z 13.3°N 143.0°W 30 KT 35 MPH...POST-TROPICAL/REMNANT LOW
72 hour 08/08 0000Z 13.3°N 146.4°W 30 KT 35 MPH...POST-TROPICAL/REMNANT LOW
96 hour 08/09 0000Z 13.3°N 150.0°W 30 KT 35 MPH...POST-TROPICAL/REMNANT LOW
120 hour 08/10 0000Z 13.3°N 153.8°W 30 KT 35 MPH...POST-TROPICAL/REMNANT LOW

Track forecast



Figure 2. My forecast track for Gil.



Henriette

Tropical Storm Henriette continues to strengthen as of the 0300Z advisory from the NHC:

Wind: 50 mph, with higher gusts
Location: 12.0°N 127.6°W
Movement: W at 8 mph
Pressure: 1002 mb

The tropical storm continues to battle east-northeasterly to easterly shear, with microwave and satellite data accentuating that the center is confined to the northeastern portion of the thunderstorm activity.



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

Since the shear does appear to be decreasing as forecast, Henriette is still expected to strengthen, and is still expected to become a hurricane. Most of the statistical intensity guidance thinks Henriette will become at least a mid-range Category 1 hurricane, and my updated intensity forecast is largely the same as the one from yesterday. Near the end of the forecast period, the cyclone is forecast to move across the 26C isotherm and move into a somewhat more stable airmass; this combination is likely to end in weakening. The intensity forecast during the day four and five period is particularly uncertain. Waters are not forecast to cool to below 25C during that portion of the forecast period, and even beyond it, so it would appear that significant weakening is likely, at least compared to the quick decay rate we're used to seeing over cooler waters in this basin. Should Henriette hang on as a tropical storm throughout the extended range, the 700 to 500 mb height fields within the global models suggest that the cyclone could pose a long-range threat to Hawaii beyond next weekend.

The track forecast remains fairly straightforward, at least in the short-term. Henriette is south of a weakening mid-level ridge. The global models respond to this evolution by steering the tropical storm west-northwestward over the next three to four days. Thereafter, some notable discrepancies arise, with the ECMWF forecasting a westward turn as the cyclone weakens and becomes shallow, while the GFS forecasts Henriette to continue gaining latitude, and forecasts only a brief period of westward motion near the 120 hour benchmark, likely in response to a local enhancement of the ridge. Since the ECMWF initialized only a weak vortex that seemed a little unrepresentative of Henriette's actual strength, I prefer to place more weight on the GFS solution, showing a long-range threat to the Hawaiian Islands. Interests there should carefully monitor the progress of Henriette over the next week.

Intensity forecast and track positions

INITIAL 08/05 0300Z 12.0°N 127.6°W 45 KT 50 MPH
12 hour 08/05 1200Z 12.4°N 128.7°W 50 KT 60 MPH
24 hour 08/06 0000Z 12.9°N 130.5°W 55 KT 65 MPH
36 hour 08/06 1200Z 13.5°N 132.1°W 60 KT 70 MPH
48 hour 08/07 0000Z 14.3°N 134.1°W 70 KT 80 MPH
72 hour 08/08 0000Z 15.2°N 136.0°W 75 KT 85 MPH
96 hour 08/09 0000Z 15.7°N 138.0°W 65 KT 75 MPH
120 hour 08/10 0000Z 16.4°N 139.8°W 50 KT 60 MPH

Track forecast



Figure 4. My forecast track for Henriette.



Elsewhere

Elsewhere, the tropics are fairly benign at the moment. The GFS forecasts the development of another tropical cyclone following Henriette in about seven days. The GFS has also been consistent in forecasting the development of a weak tropical storm north of the Cape Verde Islands around the same time.

2013 Pacific hurricane season Tropical Depression Gil Tropical Storm Henriette

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Tropical weather analysis - August 4, 2013

By: KoritheMan, 6:58 AM GMT on August 04, 2013

Gil

Gil continues to weaken. As per the 0300Z NHC advisory, the following information was available on the storm:

Wind: 50 mph, with higher gusts
Location: 15.3°N 134.3°W
Movement: W at 9 mph
Pressure: 1001 mb

If the cyclone didn't run out of Gil yesterday, it certainly appears to have done so today. All of the deep convection has eroded, primarily due to northwesterly shear; in addition, recent total precipitable water imagery from the University of Wisconsin CIMSS webpage suggests that Gil may have entrained a little bit of dry air along its western periphery, likely reaffirmed by the shear. Satellite estimates are plummeting as fast as the Dvorak technique allows, and Gil may very well already be a tropical depression, rather than a tropical storm.



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

Although Gil is forecast to move southwestward into an environment of somewhat lighter shear, water vapor imagery continues to suggest northerly to northwesterly upper-level winds extending down to at least 13N; since Gil is not expected to get below that latitude, the potential for restrengthening later in the period appears diminutive. The GFS continues to suggest the environmental northerlies will decrease and Gil will find itself in a more favorable wind shear environment, but this model has stubbornly relaxed the shear in the area over the last several days to no avail. Given current trends, Gil will likely dissipate later today if convection does not return to the low-level center soon. In contrast to previous forecasts, I will forecast dissipation of Gil in 72 hours, although it could occur much sooner.

Gil remains south of a mid-level ridge, which is forecast to strengthen. Lacking any synoptic scale features that would cause a weakness of any sort, I will continue to forecast a rather aclimatological west-southwestward to southwestward motion over the next couple of days, with a turn back to the west thereafter. The model guidance remains in good agreement on this scenario, and even the GFS, which was previously a northern outlier near the end of the period, has come into better agreement with the other models in keeping Gil on a more southerly track.

Intensity forecast and positions

INITIAL 08/03 0300Z 15.3°N 134.3°W 45 KT 50 MPH
12 hour 08/03 1200Z 14.8°N 134.3°W 40 KT 45 MPH
24 hour 08/04 0000Z 14.4°N 135.5°W 35 KT 40 MPH
36 hour 08/04 1200Z 13.7°N 137.4°W 35 KT 40 MPH
48 hour 08/05 0000Z 13.2°N 139.5°W 30 KT 35 MPH
72 hour 08/06 0000Z 13.2°N 143.3°W 30 KT 35 MPH...POST-TROPICAL/REMNANT LOW
96 hour 08/07 0000Z...DISSIPATED

Track forecast



Figure 2. My forecast track for Gil.



Tropical Depression Eight-E

Tropical Depression Eight-E developed on Saturday from the persistent area of low pressure that has hung around big brother Gil for the last several days. As of the 0300Z NHC advisory, the following information was available on the cyclone:

Wind: 35 mph, with higher gusts
Location: 12.7°N 124.9°W
Movement: W at 10 mph
Pressure: 1008 mb

The satellite presentation is rather impressive, with a large area of very cold cloud tops exceeding -80C. The low-level center is very difficult to locate lacking any recent reliable microwave or scatterometer passes, but my best estimate, which is primarily based on extrapolation, is that it lies roughly in the center of the convective overcast, just to the north of the deepest convection.



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

The depression appears to be near the threshold of tropical storm strength, and it is probably one as I write this. Environmental conditions appear quite conducive to intensification, with the possibility of rapid intensification during the next 24-36 hours if the cyclone can develop an inner core. Water vapor imagery shows northwesterly upper flow to the north of the system, but the orientation of these winds relative to the cyclone center is such that the depression is experiencing less of a shearing influence and more of an expanding outflow mechanism, particularly in the northern quadrant of the circulation. This weakly diffluent environment is favorable for intensification, and the GFS builds an anticyclone over the depression over the next couple of days.

I am a little hesitant to forecast rapid intensification for more reasons than one, but most important of all, it's because, as the National Hurricane Center said in the 0300Z forecast discussion for the storm, Gil struggled immensely in roughly the same location as the depression less than a week ago, and memories of that are still fresh in my mind. While rapid intensification is not being explicitly indicated lacking any definitive proof that it's going to happen, I do suggest a quick rate of intensification over the next 72 hours, with the cyclone reaching a peak of 75 kt in 72 hours; this forecast is a little bit above the latest intensity consensus, and similar to the SHIPS model. Beyond 72 hours, sea surface temperatures cool along the forecast track, and the environmental airmass becomes drier. As a result, steady weakening is forecast at later time periods, and it is certainly possible this weakening could be more rapid than I have indicated below.

Like with Gil, the synoptic steering environment around the depression is well-defined and the mechanisms fairly straightforward. The tropical cyclone is south of a mid-level ridge, and appears to be pretty much on track with the 0300Z NHC forecast. A continued mostly westward motion is anticipated for the next 36-48 hours, after which the global models show the depression nearing a break in the subtropical ridge caused by a large upper low off the coast of California. The models show this feature amplifying and moving southward, dragging a mid- to upper-level trough with it. Even though the depression is expected to weaken late in the period, it may not do so fast enough to avoid threatening Hawaii next weekend, and interests there should begin to monitor the progress of this system over the next several days. The global model synoptic fields indicate that, should the depression weaken more abruptly on days four and five, it would have a propensity toward the lower-tropospheric flow, which would consequently induce a more westward motion well to the south of those islands. Even if the depression does somehow come close to Hawaii, it will likely meet the same fate as Flossie, and only bring rain showers to the archipelago.

Intensity forecast and positions

INITIAL 08/04 0300Z 12.7°N 124.9°W 30 KT 35 MPH
12 hour 08/04 1200Z 12.6°N 126.0°W 35 KT 40 MPH
24 hour 08/05 0000Z 12.6°N 127.1°W 45 KT 50 MPH
36 hour 08/05 1200Z 12.7°N 128.5°W 50 KT 60 MPH
48 hour 08/06 0000Z 13.3°N 130.3°W 65 KT 75 MPH
72 hour 08/07 0000Z 15.1°N 135.1°W 75 KT 85 MPH
96 hour 08/08 0000Z 16.3°N 138.3°W 65 KT 75 MPH
120 hour 08/09 0000Z 17.5°N 142.5°W 50 KT 60 MPH

Track forecast



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

Tropical Storm Gil Tropical Depression Eight-E 2013 Pacific hurricane season

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Tropical weather analysis - August 3, 2013

By: KoritheMan, 7:14 AM GMT on August 03, 2013

Invest 91L

An area of low pressure located about 70 miles east of Cape Canaveral, Florida is associated with the remnants of Tropical Storm Dorian. Satellite and radar data suggest that the associated thunderstorm activity has been steadily increasing over the last several hours. Based on the limited surface observations available, along with scatterometer-derived surface wind data, 91L appears close to being a tropical depression, if it is not already one now.



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

There is some northwesterly shear over the system, and my best gander at the location of the low-level center is along the northern edge of the convective canopy. Despite the northwesterly shear, atmospheric conditions appear at least marginally conducive for some additional development, and this system may well become a tropical cyclone later today. By Sunday, the global models suggest that 91L will become entangled with an approaching cold front. There is the possibility of baroclinic intensification as an extratropical cyclone thereafter, but those processes are more suited for near-term forecasts, and not short to medium range speculation.

Water vapor imagery shows that the initial shortwave trough over the eastern United States has pretty much departed, with a sharp gradient of northwesterly mid-level winds over much of that area. The imagery also reveals another impulse -- this one all the way up in Quebec -- that is likely to reamplify the weakness in this area and cause the system to move northward later today, followed by a turn toward the northeast thereafter. Since the trough appears to have departed a little sooner than forecast, I would presume that there will be a temporary rebuilding of the subtropical ridge to the north of the low pressure center during the next 12-24 hours, which may allow the center to come farther west, on a track closer to the Outer Banks of North Carolina; this is supported by UW-CIMSS steering imagery as well, which does indeed show that the ridge over the central Atlantic has shifted westward in the last six hours, closer to the center of Invest 91L. While I am not currently anticipating a landfall, I do expect some westward shifts in the dynamical guidance over the next cycle or two, and the margin for error is enough that interests along the Outer Banks should monitor the progress of this system.

The circulation associated with this feature is small, and the shear will keep the heaviest precipitation and strongest winds to the southeast and east of the low-level center. Because of this, even if the system becomes a tropical cyclone again, watches and warnings will not be required for any portion of the Florida east coast. Rainfall will also not be a significant issue, and the left side of Northern Hemispheric tropical cyclone is typically considered to be subsident as well.

Probability of development in 48 hours: 60%

Gil

Gil dropped below hurricane strength yesterday. As of the 0300Z NHC advisory, the following information was available on Gil:

Wind: 65 mph, with higher gusts
Location: 14.9°N 130.6°W
Movement: W at 12 mph
Pressure: 995 mb

Gil was completely devoid of deep convection earlier, but a new burst has developed over the low-level center in the last several hours. Satellite estimates suggest that Gil is still a strong tropical storm, and it is likely that the temporary cessation of deep convection from the cyclone center earlier was not sufficient to weaken the storm just yet.



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

Water vapor imagery suggests that Gil continues to experience westerly shear, and the corresponding outflow signature in that direction is rather flat as a result; in addition, there was some dry air entrainment into the circulation earlier, and that may continue to be the case as the westerlies continue.

The intensity forecast is quite a challenge this morning. The GFS suggests that the environment could become more favorable over the next day or so, but this model is clearly not handling the shear in the near-storm environment particularly well, so I am not sure how logical it is to rely on it in this instance. Since there are no signs of the shear easing up over the next couple of days, I have chosen to forecast additional weakening during the first 48 hours of the forecast. After that time, the GFS -- hopefully performing a little better this time around -- shows the environment becoming more favorable as Gil heads farther south, which would agree well with high cloud motions derived from water vapor imagery. Thus, some restrengthening is shown at that time. In about four days, the SHIPS model shows water temperatures cooling a little (but still remaining at or above 26C), which may not allow for robust intensification. An alternate scenario is that Gil succumbs to the presently hostile environment and runs out of Gil in the next 48 hours.

Recent satellite fixes suggest that Gil's center is a little north of the 0300Z NHC advisory position, which I reflect in my 0600Z of the storm below. The cyclone appears to be moving pretty much due west, and this motion is expected to continue in the short-term. Within the next 12-24 hours, the global models strengthen the ridge to the north of Gil, which is expected to force the cyclone to turn toward west-southwest. The GFS and ECMWF have somewhat differing positions in where the Gil vortex ends up in five days, but for all practical purposes, there is a solid enough consensus that confidence in the forecast track is relatively high.

One fly in the ointment is the possibility of a Fujiwhara interaction of sorts with a tropical disturbance to the east. Since Gil still appears to be the stronger of the system, and thus far shows no signs of interacting with the disturbance, my forecast is basically an update of the NHC forecast track.

Although Gil will enter the central Pacific on Tuesday, it will remain far to the south of Hawaii, probably far enough to not even provide any locally increased surf.

Intensity forecast and positions

INITIAL 08/03 0600Z 15.2°N 131.2°W 55 KT 65 MPH
12 hour 08/03 1800Z 15.2°N 132.3°W 55 KT 65 MPH
24 hour 08/04 0600Z 14.8°N 133.9°W 45 KT 50 MPH
36 hour 08/04 1800Z 14.4°N 135.8°W 40 KT 45 MPH
48 hour 08/05 0600Z 13.8°N 137.8°W 40 KT 45 MPH
72 hour 08/06 0600Z 13.4°N 140.0°W 45 KT 50 MPH
96 hour 08/07 0600Z 13.3°N 142.4°W 45 KT 50 MPH
120 hour 08/08 0600Z 13.3°N 144.9°W 45 KT 50 MPH

Track forecast



Figure 3. My forecast track for Gil.

Invest 90E

A persistent area of low pressure continues to linger several hundred miles east of Gil. Convection associated with this area is not well-organized, although earlier scatterometer data and recent microwave pictures suggest a fairly robust surface circulation. Thus, if convection can persist and organize, it will not take a lot of time for this system to become a tropical cyclone.



Figure 4. Latest infrared satellite image of Invest 90E. Image credit: NOAA's Satellite Services Division (SSD).

Since Gil is now in a better established steering regime, the distance between the two system is increasing, raising the potential for development with 90E. The disturbance is expected to move westward for the next 24-36 hours, after which time a turn toward the west-northwest is forecast as the system approaches a small break in the subtropical ridge, in agreement with the guidance.

Cooler waters await the system in about four days, so if it's going to develop, it has to do it within the next 72 hours. This system is not a threat to any landmasses.

Probability of development in 48 hours: 50%

Tropical Storm Gil Invest 90E Invest 91L

Updated: 7:21 AM GMT on August 03, 2013

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