KoritheMan's WunderBlog

Tropical weather analysis - May 29, 2012

By: KoritheMan, 8:41 PM GMT on May 29, 2012

Beryl

Beryl is centered over southeastern Georgia, and is still a tropical cyclone. As of this morning's advisory from the NHC, the following was posted:

Wind: 30 mph, with higher gusts
Location: 31.8°N 82.5°W
Movement: NE at 8 mph
Pressure: 1005 mb
Category: Tropical depression (Saffir-Simpson Hurricane Scale)

The satellite presentation remains impressive, and all parameters appear present for Beryl to regain tropical storm strength as it emerges over the western Atlantic tomorrow morning.



Figure 1. Latest visible satellite image of Tropical Depression Beryl, courtesy of RAMMB imagery from Colorado State University (CSU).

By late Thursday, Beryl is forecast to lose tropical characteristics and then become absorbed by a larger extratropical system. The models are in better agreement on this today, showing a large and powerful extratropical low centered east of Newfoundland during that time.

Coastal and offshore reports indicate that winds are increasing, although there are no indications of winds higher than 25 kt at this time. Winds overland remain fairly light, although there are probably still some spots of 20-30 mph wind gusts in some of the heavier rainbands east of the center. Despite the forecast reintensification of Beryl, and the close distance to the North Carolina coast forecast to be reached Wednesday evening, westerly shear should keep much of the associated convection downstream from the North Carolina coast. Hence, tropical storm warnings will probably not be reissued. Unfortunately, this also means that Beryl's rains are unlikely to put a significant dent in the drought across that region, although a swath of 1 - 3 inches is still possible through tomorrow.

5-intensity forecast

INITIAL 05/29 2100Z 25 KT 30 MPH...INLAND
12 hour 05/29 0600Z 30 KT 35 MPH...INLAND
24 hour 05/30 1800Z 35 KT 40 MPH...OVER WATER
36 hour 05/31 0600Z 40 KT 45 MPH
48 hour 06/01 1800Z 45 KT 50 MPH
72 hour 06/02 1800Z 45 KT 50 MPH...EXTRATROPICAL
96 hour 06/03 1800Z...ABSORBED BY LARGER EXTRATROPICAL LOW

5-day track forecast



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

Also yes, I realize my forecast points are a little off, because I was still in the process of writing this as the new advisory was coming out. Sue me. >_>

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Tropical weather analysis - May 29, 2012

By: KoritheMan, 7:28 AM GMT on May 29, 2012

Beryl

Although now a mere depression, Beryl continues to produce heavy rains and strong winds over coastal waters. As of the latest NHC advisory, the following information was posted on Beryl:

Wind: 30 mph, with higher gusts
Location: 30.8°N 83.4°W
Movement: NW at 5 mph
Pressure: 1005 mb
Category: Tropical depression (Saffir-Simpson Hurricane Scale)

Satellite images still indicate a fairly well-organized cloud pattern, especially for a system that's been inland for about 24 hours. This is probably attributable to the cyclone's close proximity to the Gulf of Mexico and/or western Atlantic.



Figure 1. Latest infrared satellite image of Tropical Depression Beryl, courtesy of RAMMB imagery Colorado State University (CSU).

In addition, doppler radar out of Jacksonville, Florida still depict fairly vigorous rainbands lashing a large portion of central and northern Florida, into southern Georgia. The west side of the circulation remains devoid of deep convection due to a subsident airmass being injected into Beryl by an approaching upper trough, and perhaps a bit of westerly shear.

Beryl is still generating strong winds within the aforementioned bands, according to coastal and offshore surface reports, especially in gusts. Because Beryl is a slow-moving system, these winds are expected to persist into at least tomorrow evening. However, as the cyclone accelerates, it will carry the rough weather with it. Strong winds and heavy rainfall should continue impacting coastal sections of the southeastern United States from northern Florida to the North Carolina Outer Banks through Wednesday. Impacts will occur on a west-to-east basis. I am not real fond of any impending tornado threat, as upper air soundings over areas along the projected path still don't portray very favorable hodograph patterns. Only one tornado is reported to have occurred in association with Beryl thus far: an unrated tornado struck approximately 3 miles east of Port St. Lucie on the east coast of Florida at 1903 UTC local time yesterday (Monday). The tornado caused some minor roof damage, but no injuries or fatalities.

Because of the strong winds, the threat of rip currents along the coast is also extant, and any swimmers should stay out of the water. Rip currents are one hazard that seem relatively innocuous at first glance, but, like flooding, the actual danger of said phenomenon generally goes unnoticed. Small craft advisories are posted for the coastal waters for all of Georgia, portions of northeast Florida, and even the Big Bend area of northwest Florida, all the way on the Gulf side.

A slew of satellite and radar fixes suggest that Beryl is slowing, and appears to be getting ready to turn northward, if it is not doing so already. This signifies Beryl's westernmost approach across the United States, and the cyclone should soon recurve under the influence of the central US trough. Thereafter, the cyclone is forecast to reemerge into the western Atlantic, where a brief period of reintensification as a tropical cyclone is possible. By late Thursday or early Friday, Beryl is expected to become extratropical while racing across the north Atlantic shipping lanes. Model guidance remains in excellent agreement with the track, but differ with respect to whether Beryl or the trough will remain a distinct entity.

Most likely, it depends on the location of the trough relative to the cyclone center, which is virtually impossible to predict this far in advance. If Beryl does remain separate from the trough, there should be enough baroclinic forcing to allow for some intensification as an extratropical cyclone. Indeed, the models that maintain Beryl as the dominant vortex show a rather strong system marching across the north Atlantic about five days from now. For the sake of continuity, I will continue to keep Beryl as a separate entity throughout the forecast period. Of course, I am prepared to be burned.

5-day intensity forecast

INITIAL 0900Z 05/29 25 KT 30 MPH...INLAND
12 hour 1800Z 05/29 25 KT 30 MPH...INLAND
24 hour 0600Z 05/30 25 KT 30 MPH...INLAND
36 hour 1800Z 05/30 30 KT 35 MPH...OVER WATER
48 hour 0600Z 05/31 35 KT 40 MPH
72 hour 0600Z 06/01 40 KT 45 MPH...EXTRATROPICAL
96 hour 0600Z 06/02 45 KT 50 MPH...EXTRATROPICAL
120 hour 0600Z 06/03 50 KT 60 MPH...EXTRATROPICAL

It should be noted that the latter portion of the intensity forecast is highly speculative, due to uncertainty in how Beryl will interact with the trough. However, there is time to reevaluate later.

5-day track forecast



Figure 2. My 5-day forecast for Beryl.

Tropical storm warnings are unlikely to be reissued even as Beryl strengthens, as the GFS indicates the upper tropospheric flow in the vicinity of the cyclone will be almost uniformly westerly, which would effectively prevent the strongest winds from reaching the coast.

Hurricane

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Tropical weather analysis - May 28, 2012

By: KoritheMan, 9:15 AM GMT on May 28, 2012

Beryl

Beryl made landfall a few hours ago in northeastern Florida near Jacksonville as a high-end tropical storm. Satellite and radar data indicate that the cyclone developed tropical characteristics Sunday afternoon. As of the latest NHC advisory, the following was posted:

Wind: 50 mph, with higher gusts
Location: 30.3°N 82.0°W
Movement: W at 8 mph
Pressure: 997 mb
Category: Tropical storm (Saffir-Simpson Hurricane Scale)

It should be noted that Beryl was just under hurricane strength at landfall. Jacksonville, Florida reported a wind gust to 47 mph just after midnight local time, while the center of Beryl was just east of the city. Tropical storm force winds will continue to gradually overspread areas of northern Florida and southern Georgia this morning and into today as Beryl moves farther inland. Combined with periods of heavy rainfall, these winds will likely cause some power outages and tree damage. Doppler estimated rainfall totals indicate that a large swath of 1 - 4 inches of rain have fallen across central and northern Florida in advance of Beryl's center. Additional heavy rainfall is expected through Monday, and Beryl could produce rainfall totals of 3 to 6 inches over central and northern Florida, into southern Georgia. The threat for isolated tornadoes continues, although no tornado watches have been issued by the Storm Prediction Center thus far, and no tornadoes have been reported. 0z upper air soundings from Jacksonville did not show a particularly favorable environment for tornadic development, although a couple cells here and there appear to occasionally rotate as per doppler radar imagery.



Figure 1. Latest infrared satellite image of Tropical Storm Beryl, courtesy of NOAA's Satellite Services Division (SSD).

Beryl should soon turn west-northwest and then northwest, as the ridge to the north erodes in advance of an approaching shortwave trough. This trough will ultimately force Beryl back out into the Atlantic in about two days. In the meantime, the storm's slow movement will linger a heavy rainfall threat, although serious flood potential will likely be mitigated by the ongoing drought in this region. Model guidance remains in excellent agreement on the future trajectory. Isobaric fields within the global and dynamical models suggest that Beryl should become extratropical on Friday. Before that though, reintensification as a tropical cyclone is expected as the system reenters the western Atlantic. Baroclinic deepening once the system loses tropical characteristics is also anticipated.

As a bit of trivia, Beryl is the earliest tropical storm landfall in the United States since Tropical Storm Arlene in 1959 struck the central coast of Louisiana on May 30.

5-day intensity forecast

INITIAL 0900Z 05/28 45 KT 50 MPH...INLAND
12 hour 1800Z 05/28 35 KT 40 MPH...INLAND
24 hour 0600Z 05/29 30 KT 35 MPH...INLAND
36 hour 1800Z 05/29 30 KT 35 MPH...INLAND
48 hour 0600Z 05/30 30 KT 35 MPH...INLAND
72 hour 0600Z 05/31 35 KT 40 MPH...OVER WATER
96 hour 0600Z 06/01 40 KT 45 MPH...EXTRATROPICAL
120 hour 0600Z 06/02 50 KT 60 MPH...EXTRATROPICAL

5-day track forecast



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

It should be noted that even as the center moves inland, bands of heavy rain containing tropical storm force winds will linger across coastal sections of northeast Florida and southern Georgia. This is typical of inland-moving systems, particularly ones that are slow-moving like Beryl. For this reason, the active tropical storm warnings will probably remain in place for awhile longer. Marine interests should not venture outside during such duress.

Watches and warnings

THE TROPICAL STORM WARNING HAS BEEN DISCONTINUED NORTH OF THE
SAVANNAH RIVER.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* FLAGLER BEACH FLORIDA TO THE SAVANNAH RIVER GEORGIA

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

Hurricane

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Tropical weather analysis - May 27, 2012

By: KoritheMan, 7:08 AM GMT on May 27, 2012

Beryl

Subtropical Storm Beryl continues moving toward the southeast United States. As of the latest NHC advisory, the following was posted on the storm:

Wind: 50 mph, with higher gusts
Location: 30.8°N 77.9°W
Movement: WSW at 7 mph
Pressure: 998 mb
Category: Subtropical storm (Saffir-Simpson Hurricane Scale)

Beryl has not shown any signs of acquiring tropical characteristics thus far, with the exhibited cloud pattern still very reminiscent of a subtropical storm. However, recent satellite pictures show a stronger, more persistent convective pattern.



Figure 1. Latest infrared satellite image of Subtropical Storm Beryl, courtesy of NOAA's Satellite Services Division (SSD).

It is uncertain whether this heralds the onset of a warm core, or if it's just a fluke. CIMSS 200 mb vorticity analysis suggests that the upper-tropospheric cold low that was following Beryl has moved to the south, closer to the Bahamas, but this is not supported by water vapor imagery. Regardless, it is still anticipated that Beryl will become tropical sometime before landfall. Nearby buoy observations indicate that Beryl is traversing sea surface temperatures between 26°C and 27°C. These values are just warm enough to support a tropical storm, and with the upcoming diurnal convective maximum period, we may see Beryl try to pull off one final accolade. Another factor supporting a warm core transition is the recent contraction of the wind field; currently, tropical storm force winds extend out to only about 90 miles from the low-level center. This is in sharp contrast to this time yesterday, when they were about 25% larger.

Interestingly, the GFS forecasts about 20 kt of northerly upper-level flow to develop over Beryl today, and persist until landfall. There are no clear cut indications of that happening at this time, and I am uncertain whether this shear is related to the storm itself, or to the central United States ridge, which is forecast to slide eastward today. Lacking any large scale features to induce this shear, the ridge seems highly suspect. The only other factor I could conceivably see generating that kind of shear is for the upper low Beryl is sitting under to back out from underneath the surface low and move southeast. That is not happening at this time. In deference to this shear, I will hold off on intensifying Beryl.

5-day intensity forecast

INITIAL 05/27 0300Z 45 KT 50 MPH
12 hour 05/27 1200Z 45 KT 50 MPH...TROPICAL
24 hour 05/28 0000Z 45 KT 50 MPH...INLAND
36 hour 05/28 1200Z 35 KT 40 MPH...INLAND
48 hour 05/29 0000Z 30 KT 35 MPH...INLAND
72 hour 05/30 0000Z 30 KT 35 MPH...OVER WATER
96 hour 05/31 0000Z 40 KT 45 MPH
120 hour 06/01 0000Z 45 KT 50 MPH...EXTRATROPICAL

The type of strengthening shown after the system emerges into the Atlantic is still not certain. Whether Beryl intensifies tropically or baroclinically on Wednesday more than likely depends on the sharpness and location of recurvature. The ECMWF is farther north, which places Beryl closer to the cooler shelf waters off the southeast coast, and also closer to a large belt of westerly shear forecast to develop over the western Atlantic at that time. The models which are farther south suggest Beryl will cling to tropical characteristics a little longer, and possibly reintensify as a tropical cyclone. The models are unanimous, however, that the cyclone will lose tropical characteristics on Thursday, as a large upper-level trough and attendant cold front encroach on it from the west.

Anyway, I tend to side with the southern solution, as Beryl isn't expected to strengthen much.

5-day forecast track



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

Notice my track is a fair bit south of the National Hurricane Center's after landfall, but gradually comes into better agreement.

Tropical storm force winds are forecast to begin affecting the southeastern United States coast today. Already, coastal reports indicate winds of about 20 to 25 mph lie just offshore the South Carolina coast. These winds will gradually spread westward and onto the coast with time. Beryl may also produce isolated tornadoes and heavy rainfall.

Watches and warnings

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* VOLUSIA/BREVARD COUNTY LINE FLORIDA TO EDISTO BEACH SOUTH CAROLINA

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

Updated: 8:43 AM GMT on May 27, 2012

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Tropical weather analysis - May 26, 2012

By: KoritheMan, 7:08 AM GMT on May 26, 2012

Beryl

Let's get right down to it: this is unusual. Nearly unprecedented even. Subtropical Storm Beryl formed off the coast of the Carolinas late Friday evening. According to historical records, the last time two named storms occurred in May was during 1887. It should be noted that there is little correlation to early season activity with the rest of the season. However, I am finding it increasingly difficult to believe CSU's April forecast of a mere 10 named storms. Besides that, the pattern this year favors more homegrown storms than we have seen in recent years, which might help to inflate the numbers somewhat. When the eastern Atlantic is shut down (which we should expect, due to increasing westerly shear associated with the oncoming El Nino), tropical waves tend to wait until reaching a more favorable longitude before transforming into tropical cyclones. This has been the case so far in 2012, with Alberto and Beryl both forming in the western Atlantic less than 200 miles from the United States coast.

As of the latest NHC advisory, the following was posted on Beryl:

Wind: 45 mph, with higher gusts
Location: 32.4°N 75.1°W
Movement: W at 2 mph
Pressure: 1001 mb
Category: Subtropical storm (Saffir-Simpson Hurricane Scale)

The center remains exposed to the east of a large band of deep convection that is just grazing the North Carolina Outer Banks. Convection is virtually nonexistent over the cyclone center at this time, but recent satellite and long-range doppler radar loops suggest this convection may be slowly attempting to wrap into the center. Also, some weak upper-level outflow has developed on the western flank of the circulation.



Figure 1. Latest infrared satellite image of Subtropical Storm Beryl, courtesy of NOAA's Satellite Services Division (SSD).

Vertical shear over the system is decreasing, outflow is developing, and examination of water vapor and satellite imagery suggests that Beryl is dismantling itself from the trough to the east. This triple point gives me reason to believe that Beryl may transition to a tropical storm sooner rather than later, although earlier AMSU microwave data still indicated a mostly cold core system. Additionally, the cyclone is still caught beneath an upper low, particularly well-defined from 300 to 100 mb. This may temporarily slow the transformation process.

The mid-level flow over the central United States is quickly becoming zonal, which is helping to push the ridge southward to the east of Beryl. Simultaneously, the cyclone is being influenced by the aforementioned trough. A combination of the northeasterly flow on the east side of the ridge, and the northwesterly flow on the west side of the trough is effectively preventing much movement. However, since Beryl is drifting west, the ridge is clearly becoming the dominant steering mechanism. As the mid-level flow over the storm strengthens, Beryl is expected to respond by accelerating and moving west-southwest or southwest. Then, on Sunday, a westward turn toward the southeast United States is expected as the cyclone rounds the southern periphery of the Atlantic ridge. I am a bit to the south of the model consensus, and agree pretty strongly with what the National Hurricane Center is currently saying.

Beryl is expected to move back into the Atlantic on late Tuesday or early Wednesday as it begins to feel the influence of a deep-layered trough forecast to amplify across the central United States on Monday. Analysis of upper-level winds during that time suggest that some reintensification is possible, although how much of that will be tropical or baroclinic remains to be seen.

Interests along the southeast United States from South Carolina to northern Florida should monitor the progress of Beryl.

5-day intensity forecast

Initial 05/26 0300Z 40 KT 45 MPH
12 hour 05/26 1200Z 40 KT 45 MPH
24 hour 05/27 0000Z 45 KT 50 MPH...BECOMING TROPICAL
36 hour 05/27 1200Z 50 KT 60 MPH
48 hour 05/28 0000Z 55 KT 65 MPH...NEAR THE NORTHERN FLORIDA COAST
72 hour 05/29 0000Z 35 KT 40 MPH...INLAND
96 hour 05/30 0000Z 30 KT 35 MPH...INLAND
120 hour 05/31 0000Z 30 KT 35 MPH...OVER WATER

I am not too enthusiastic about a quick inland decay rate, since the system is forecast to stall after landfall, which will put it in close proximity to the warm waters of the Gulf Stream. It should also be noted that there is considerable uncertainty in my intensity forecast, since predicting tropical transition is rather difficult. Also, cyclones in this part of the world tend to, more often than not, ingest dry continental air into their circulations, which can interrupt the strengthening process.

5-day track forecast



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

Given quasi-stationary movement expected after landfall, Beryl has the potential to produce flash flooding across portions of the southeast United States into early next week.

Watches and warnings

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* VOLUSIA/BREVARD COUNTY LINE FLORIDA TO EDISTO BEACH SOUTH CAROLINA

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* EDISTO BEACH TO SOUTH SANTEE RIVER SOUTH CAROLINA

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

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

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

Bud

As quickly as it strengthened, Bud has fallen apart. As of the latest NHC advisory, the following was posted on the decaying cyclone:

Wind: 50 mph, with higher gusts
Location: 20.2°N 105.8°W
Movement: N at 7 mph
Pressure: 1002 mb
Category: Tropical storm (Saffir-Simpson Hurricane Scale)

Even being completely free of convection, the center of Bud is difficult to locate, to say the least. In fact, the cyclone resembles a post-tropical remnant low, rather than a tropical cyclone. Nonetheless, Dvorak constraints disallow for abrupt weakening, which is the likely reason the National Hurricane Center has decided to keep Bud as a tropical storm for now. In any case, the system has become very disorganized, with satellite imagery indicating that the mid-level is racing northward, leaving the low-level center behind.



Figure 3. Latest infrared satellite image of Tropical Storm Bud, courtesy of NOAA's Satellite Services Division (SSD).

Given the disheveled satellite appearance, as well as the fact that a portion of the circulation is already overland, Bud has probably dissipated. What's left of the low-level circulation should quickly decouple over the mountainous terrain of western Mexico.

Although I have indicated a westward turn today, given the close interaction with the rugged terrain, a more plausible scenario is probably that the cyclone, or its remnants, will move erratically until losing their identity in about 24 hours. It might not even take that long.

All watches and warnings will likely be lowered on the next NHC advisory.

5-day intensity forecast

Initial 05/26 0300Z 45 KT 50 MPH
12 hour 05/26 1200Z 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW
24 hour 05/27 0000Z 20 KT 25 MPH...DISSIPATED

5-day track forecast



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

Watches and warnings

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* THE COAST OF MEXICO FROM MANZANILLO WESTWARD TO CABO CORRIENTES

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* THE COAST OF MEXICO FROM NORTH OF CABO CORRIENTES TO SAN BLAS

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

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

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

Bud still poses a heavy rainfall threat given its proximity to the Pacific, but it is likely that any serious flood potential will be mitigated by the lack of convection.

Hurricane

Updated: 7:18 AM GMT on May 26, 2012

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Tropical weather analysis - May 24, 2012

By: KoritheMan, 2:51 AM GMT on May 25, 2012

Invest 94L

A large area of low pressure centered just north of Grand Bahama continues to become better organized. This time yesterday I wasn't enthusiastic on development, as I wanted to see how it fared against continuing westerly shear and interaction with Cuba. It has done rather well for itself though, and all indications are that it will eventually become the second named storm of the season.

Satellite and surface observations indicate that this low is becoming better organized, with large pressure falls noted over the western Bahamas this afternoon. Large scale pressure falls during the daylight hours, when oceanic convection is weakest, is usually a sign of impending development, all other things being equal. Convection is also forming nearer to the central gyre, further attesting to the valiant organization of the system.



Figure 1. Latest infrared satellite image of Invest 94L, courtesy of RAMMB imagery Colorado State University (CSU).

Vertical shear over the system is still rather strong at the moment, as evidenced by the squashed convective pattern, but is forecast to slowly diminish, and 94L could become a tropical depression or tropical storm by tomorrow evening or early Saturday. The global models unanimously predict a tropical cyclone to emerge from this, and at this point, denial will get me nowhere.

The system is sandwiched between two cold lows, one over the central Gulf of Mexico, and another over Virginia moving out into the Atlantic. The former low is forecast to dissipate by tomorrow, and the latter one is of course moving into the Atlantic. In the wake of both systems, the Atlantic subtropical ridge is forecast to rebuild and force the system back toward the west, ultimately forcing a landfall somewhere along the southeast US coast, most likely the northern Florida/southern Georgia area on Monday. Models are in excellent agreement on this.

Regardless of development, heavy rains and gusty winds will continue to impact portions of the Bahamas through at least tonight. Interests along the southeast US coast should carefully monitor the progress of this system.

Probability of genesis in the next 48 hours: 60%

Should 94L become a tropical storm, it would be the first time two tropical storms formed in May since 1887. However, early season activity does not correlate to seasonal activity as a whole, and with the oncoming El Nino, I still think this season will be only slightly above average.

Bud

Bud continues to intensify, and is now a major hurricane. This is another oddity from a historical vantage point; the last time a major hurricane occurred during the month of May was in 2002. As of the latest NHC advisory, the following was posted:

Wind: 115 mph, with higher gusts
Location: 17.1°N 105.9°W
Movement: NE at 10 mph
Pressure: 960 mb
Category: 3 (Saffir-Simpson Hurricane Scale)

The hurricane is well organized on satellite images, with a 20-25 mile wide eye that seemingly shrinks due to convection. The outflow pattern is well-defined.



Figure 2. Latest infrared satellite image of Hurricane Bud, courtesy of NOAA's Satellite Services Division (SSD).

Despite continuous forecasts of southerly shear over the last few days, there appears to be very little evidence of this on water vapor imagery. The latest SHIPS model guidance also suggests little appreciable increase in shear throughout the forecast period. The primary reason I expect Bud to weaken is cooler sea surface temperatures; the hurricane is about to reach SSTs of only 26C according to the SHIPS model. Even SSTs a couple of degrees cooler seem to have a profound negative effect on major hurricanes.

Things have changed with Bud since yesterday. The global models are now in better agreement that the hurricane will continue to accelerate, reaching the coast by early Friday evening. This is supported by real time steering analyses and water vapor imagery. Landfall should occur between Manzanillo and Puerto Vallarta. After landfall, the global model fields think that the low- and middle-tropospheric circulations will decouple, with the former lagging behind near the coast. So do I.

5-day intensity forecast

Initial 05/25 0300Z 100 KT 115 MPH
12 hour 05/25 1200Z 90 KT 105 MPH
24 hour 05/26 0000Z 80 KT 90 MPH...INLAND
36 hour 05/27 1200Z 40 KT 45 MPH...INLAND
48 hour 05/28 0000Z 30 KT 35 MPH...OVER WATER
72 hour 05/29 0000Z 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW
96 hour 05/30 0000Z...DISSIPATED

5-day track forecast



Figure 3. My 5-day forecast track for Bud.

Watches and warnings

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A HURRICANE WARNING IS IN EFFECT FOR...
* THE COAST OF MEXICO FROM MANZANILLO NORTHWESTWARD TO CABO
CORRIENTES

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* THE COAST OF MEXICO FROM PUNTA SAN TELMO WESTWARD TO EAST OF
MANZANILLO

A HURRICANE WATCH IS IN EFFECT FOR...
* THE COAST OF MEXICO FROM PUNTA SAN TELMO WESTWARD TO EAST OF
MANZANILLO

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* THE COAST OF MEXICO NORTH OF CABO CORRIENTES TO SAN BLAS

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

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

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

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

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

Hurricane

Updated: 4:11 AM GMT on May 25, 2012

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Tropical weather analysis - May 24. 2012

By: KoritheMan, 7:44 AM GMT on May 24, 2012

Invest 94L

A broad area of disturbed weather over the western Caribbean Sea is producing widespread showers and thunderstorms east of the center. Although the associated convection is quite deep, the latest SHIPS model output and CIMSS analysis depict about 40 knots of westerly shear over the system.



Figure 1. Latest infrared satellite image of Invest 94L, courtesy of RAMMB imagery Colorado State University (CSU).

With little respite from the vertical shear expected, 94L has little chance of developing. Interestingly, the global models portray a more favorable upper air pattern once the system enters the western Atlantic, and on Saturday the system could find itself left behind by the trough currently moving through the upper midwest. Then, amidst a building ridge, the system is forecast to find itself under a diffluent upper flow pattern, which the models -- including the generally reliable GFS and ECMWF -- suggest could allow the system to become a tropical cyclone. Current forecasts for the synoptic scale pattern over the United States at that time indicates a motion toward the northern Florida coast in about five days. It should be noted that the GFS forecasts an environment over the Gulf of Mexico that, although hardly favorable, isn't quite as unfavorable as we've seen in recent weeks, likely due to a temporary northward migration of the subtropical jet. This does not mean I am expecting development. It is questionable whether this system will even survive the next 24 hours. Development is not anticipated while the system is in the Caribbean.

Based on the current center position, 94L is likely to miss south Florida, although in this case, a landfall would pretty much be inconsequential, since all of the associated weather is east of the center in a disorganized band.

Regardless of development, locally heavy rainfall will continue over portions of the Cayman Islands, Cuba, the Bahamas, and south Florida through the next day or so.

Probability of genesis within the next 48 hours: 0%

Bud

Just recently, Bud has become a hurricane, the first of the Eastern Pacific season. As of the latest intermediate advisory from the National Hurricane Center, the following information was posted on the storm:

Wind: 75 mph, with higher gusts
Location: 14.5°N 107.7°W
Movement: N at 6 mph
Pressure: 987 mb
Category: 1 (Saffir-Simpson Hurricane Scale)

Bud is becoming better organized. A ragged eye is now visible in conventional satellite imagery, with a well-defined ring of convection -- no doubt an eyewall, evident in an earlier SSMI overpass. The satellite presentation and inner core have improved since then, and it is possible that the hurricane is undergoing rapid intensification. However, water vapor imagery suggests that southwesterly shear has begun to halt the westward progression of Bud's outflow, but it will take awhile yet to penetrate the inner core region.



Figure 2. Latest infrared satellite image of Hurricane Bud, courtesy of NOAA's Satellite Services Division (SSD).

Bud has about another 18 hours to do what he wants. After that, southerly shear is forecast to increase, waters are forecast to cool, and the cyclone is forecast to ingest a drier airmass. The combination of these factors should lead to weakening, especially beyond 48 hours, when the pace is predicted to become faster. The hurricane should dissipate before the end of the forecast period.

Now for the track. Bud is rounding a weakness along 110W. This should soon turn the hurricane to the north-northeast. Track models are in excellent agreement here. By late Friday and into Saturday, some notable discrepancies arise, with some forecasting the storm to move inland, and others forecasting the center to remain offshore. However, they all agree that the hurricane will come within about 150 miles of the coast regardless, which could lead to a several day period of heavy rainfall and associated flooding.

Because these models are usually reliable when in synchronicity, I will go a forecast track that blends the GFS and ECMWF together. It should be noted that Bud is becoming a large hurricane; tropical storm force winds currently extend out to 115 miles from the center, a significant change from yesterday. It would not be surprising if the wind field grew a little more. This is reflected in the official National Hurricane Center Wind Speed Probability table, which forecasts a 44% chance of tropical storm force winds in Barra Navidad through the weekend, and a 40% chance for Manzanillo. With current arrangements, Bud might not even have to make landfall to produce significant coastal impacts.

5-day intensity forecast

Initial 05/24 0300Z 65 KT 75 MPH
12 hour 05/24 1200Z 75 KT 85 MPH
24 hour 05/25 0000Z 80 KT 90 MPH
36 hour 05/25 1200Z 75 KT 85 MPH
48 hour 05/26 0000Z 65 KT 75 MPH
72 hour 05/27 0000Z 45 KT 50 MPH
96 hour 05/28 0000Z 30 KT 35 MPH
120 hour 05/29 0000Z 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW

5-day track forecast



Figure 3. My 5-day forecast track for Bud.

As a bit of trivia, the last (and only) time a May hurricane occurred alongside a previous May storm was in 1956, although record keeping in this area of the world is vastly more sparse than in the Atlantic.

Hurricane

Updated: 8:55 AM GMT on May 24, 2012

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Tropical weather analysis - May 22, 2012

By: KoritheMan, 6:22 AM GMT on May 23, 2012

Invest 94L

Apparently, the Northern Hemisphere tropics -- at least the Atlantic and Pacific, didn't bother taking a look at the calender, as there yet another area of interest in the Atlantic, "94L". The center of this broad disturbance has been quite difficult to locate, in part because westerly shear is so fast it has been masking the low cloud lines. Of course, the time of day doesn't help either. Based on a slew of observations, my best guess is somewhere between Yucatan and Grand Cayman. If true, the convection is well east of the center. CIMSS analysis diagnoses about 30 kt of westerly shear over the estimated low-level center.



Figure 1. Latest infrared of Invest 94L, courtesy of RAMMB imagery Colorado State University (CSU).

Model guidance suggests that upper-level winds could weaken somewhat over the next day or so, but would probably still be sufficient to keep the system from strengthening very much. Nonetheless, this has been a very active pattern for May, which if nothing else, is particularly interesting to me.

Water vapor imagery shows a large cutoff low moving across central Georgia. Current trends suggest that the low and its associated trough will bypass 94L, with no immediate recurvature anticipated. In about two days, another, more vigorous trough, is forecast to dive into the central US. Despite the distance of the trough relative to 94L, there should be enough of a weakness in the subtropical ridge to turn the system northeast or north-northeast toward south Florida. Model guidance is in good agreement with this. Thereafter, there are indications that the system could become trapped underneath a building ridge while moving across the western Atlantic. Such a pattern would favor a westward retrograde toward the southeast United States coast. However, there are simply too many uncertainties regarding both the synoptic pattern and the upper-level winds in the path of the system at that time, to state with any confidence what will happen in the future.

Regardless of development, locally heavy rainfall can be expected over the Cayman Islands, western Cuba, south Florida, and eventually the Bahamas.

Probability of genesis within the next 48 hours: 10%

Bud

Tropical Storm Bud continues churning in the Pacific far to the south of Mexico. Surprisingly, Bud has been a rather bewildering cyclone, in that it has not strengthened in what was deemed as a generally favorable environment. As of the most recent NHC advisory, the following was posted on the storm:

Wind: 40 mph, with higher gusts
Location: 12.9°N 105.9°W
Movement: NW at 14 mph
Pressure: 1004 mb
Category: Tropical storm (Saffir-Simpson Hurricane Scale)

Recent satellite photos suggest that Bud might finally be starting to organize, as the center is no longer exposed. A large convective burst with very cold cloud tops, up to -80C, has developed near and over the low-level center during the past couple of hours.



Figure 2. Latest infrared satellite image of Tropical Storm Bud, courtesy of NOAA's Satellite Services Division (SSD).

Upper-tropospheric outflow is well defined in all directions except the east, where it remains restricted, a symptom of easterly shear. However, high cloud motions suggest that the shear may finally be starting to diminish. Also, earlier microwave data, corroborated by recent satellite imagery, suggests Bud has developed a large and well-defined inflow band on the east side of the circulation. This southerly influx is helping to inject instability into the system, assisting intensification. Finally, this large band may, in the meantime (I expect it to dissipate as the inner wind core becomes better defined), help to shield Bud from any residual shear.

Assuming Bud is finally developing a well-defined inner core, at least steady intensification seems likely. However, the current outflow pattern is beginning to look anticyclonic, and this typically heralds strengthening. It is possible that Bud could undergo a brief period of rapid intensification if the ongoing convection persists and organizes. After 48 hours, Bud is forecast to encounter gradually increasing shear, cooler waters, and a very dry airmass near Baja. These factors should weaken the storm, and it is possible Bud will not be a tropical cyclone in five days.

The ridge to the north of Bud continues to deamplify, but water vapor imagery suggests that this process is occurring rather slowly, and the cyclone still has another 24 hours before recurving. This is a little slower than the NHC official forecast, as the ridge still looks strong. Models are in good agreement up to this point. Afterward, uncertainty arises as the express disagreement. However, the general trend over the last day or so has been for Bud to near the coast, stall, and execute a clockwise loop, presumably due to a weak low- to mid-level ridge over central Mexico.

Although a landfall is looking less likely, it wouldn't hurt to remind that, based on the running 5-year mean, there is still a 20 to 30% chance of tropical storm force winds affecting portions of the coast from Puerto Vallarta to Manzanillo. Besides, the quasi-stationary movement expected as Bud approaches the coast could produce a several day period of heavy rainfall, possibly leading to flash flooding and mudslides in areas of mountainous terrain.

5-day intensity forecast

Initial 05/24 0000Z 35 KT 40 MPH
12 hour 05/24 1200Z 45 KT 50 MPH
24 hour 05/25 0000Z 50 KT 60 MPH
36 hour 05/25 1200Z 65 KT 75 MPH
48 hour 05/26 0000Z 75 KT 85 MPH
72 hour 05/27 0000Z 65 KT 75 MPH
96 hour 05/28 0000Z 45 KT 50 MPH
120 hour 05/29 0000Z 30 KT 35 MPH

5-day track forecast



Figure 3. My 5-day forecast track for Tropical Storm Bud.

Hurricane Flood

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Tropical weather analysis - May 21, 2012

By: KoritheMan, 5:13 AM GMT on May 22, 2012

Alberto

Alberto has weakened to a tropical depression as of the latest NHC advisory:

Wind: 35 mph, with higher gusts
Location: 30.9°N 76.5°W
Movement: ENE at 13 mph
Pressure: 1008 mb
Category: Tropical depression (Saffir-Simpson Hurricane Scale)

Alberto sports a rather poor appearance on satellite imagery this evening. There is no convection near the center, and what little deep convection exists is located about 50 miles downstream from the center.



Figure 1. Latest infrared satellite image of Tropical Depression Alberto, courtesy of NOAA's Satellite Services Division (SSD).

The cyclone appears to be on the verge of decaying to remnant low, but Alberto has tricked me before, and I am a little hesitant to declare the storm dissipated. But if deep convection does not redevelop during the upcoming diurnal convective maximum period, then Alberto will likely become a remnant low late tomorrow morning.

Alberto is currently situated over the warm Gulf Stream, which is the primary reason I'm not giving up -- yet -- on one last convective burst. However, observations from drifting buoys in the western Atlantic suggest that area water temperatures cool sharply on the cyclone's projected path north of about 32N; NOAA buoy 41001, centered 150 miles east of Cape Hatteras, reported a local water temperature of 70F. These cool waters, which only get colder along the forecast track, should combine with relentless westerly shear to bring about extratropical transition of the cyclone in about 36 hours, although Alberto could dissipate before then.

There is not much to say about the track forecast. Alberto is accelerating, moving northeastward, and this general motion with additional acceleration is anticipated. The models are in good agreement with this.

5-day intensity forecast

Initial 05/22 0300Z 30 KT 35 MPH
12 hour 05/22 1200Z 25 KT 30 MPH
24 hour 05/23 0000Z 25 KT 30 MPH
36 hour 05/23 1200Z 25 KT 30 MPH...extratropical
48 hour 05/24 0000Z 25 KT 30 MPH...extratropical
72 hour 05/25 000Z...absorbed by frontal system

5-day track forecast



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

Tropical Depression Two-E

Tropical Depression Two-E is slowly organizing, and is on the verge of becoming a tropical storm. As of the latest NHC advisory, the following information was posted:

Wind: 35 mph, with higher gusts
Location: 9.8°N 101.8°W
Movement: WNW at 9 mph
Pressure: 1005 mb
Category: Tropical depression (Saffir-Simpson Hurricane Scale)

There is still some easterly shear over the depression, as evidenced by the cloud pattern. An earlier SSMIS overpass confirmed the existence of a tilted structure, with the low-level center displaced about 50 miles east of the mid-level center.



Figure 3. Latest infrared satellite image of Tropical Depression Two-E, courtesy of NOAA's Satellite Services Division (SSD).

CIMSS diagnoses only about 10 kt of shear over the depression, which is a significant decrease from yesterday. High cloud motions on satellite and water vapor imagery validate this deduction. The cyclone is slowly consolidating, as convection has formed very near the low-level center in recent satellite pictures. A further decrease in shear is expected, although in the interim, the upper flow pattern in the GFS looks more diffluent than anticyclonic. In about 24 hours, a warm ridge is forecast to develop and strengthen near or directly over the tropical cyclone. Such a pattern favors significant strengthening, and it is possible that the depression could intensify more than I am indicating. Beyond 72 hours, southerly shear may increase, but it is not expected to be enough to substantially weaken the system.

Future intensities may also be controlled by interaction with the Mexican coast; some models are now suggesting that the storm will hug the coast, veer westward, and weaken. It remains to be seen whether this will verify, but it could throw a wrench into the intensity forecast.

Water vapor imagery shows a large trough amplifying over the western United States. The ridge to the north of the depression is very shallow, and is weakening in a hurry. As such, the depression is forecast to respond accordingly by bending to the northwest. As the ridge weakens further, recurvature toward the Mexican coast is expected, but again, today's model suites have hinted at a possible suspension of inland penetration on Saturday, so the track is not as certain as it has been. For the sake of continuity, and because we still have time to monitor the progress of the western United States trough, I will continue to show the system being pulled inland by Saturday. However, I have no choice but to forecast deceleration by Friday, as suggested by large scale guidance. Further adjustments may become necessary tomorrow.

Interests along the southwest coast of Mexico from Puerto Vallarta to Manzanillo should continue to carefully monitor the progress of this strengthening system.

5-day intensity forecast

Initial 05/22 0300Z 30 KT 35 MPH
12 hour 05/22 1200Z 35 KT 40 MPH
24 hour 05/23 0000Z 50 KT 60 MPH
36 hour 05/23 1200Z 60 KT 70 MPH
48 hour 05/24 0000Z 80 KT 90 MPH
72 hour 05/25 0000Z 80 KT 90 MPH
96 hour 05/26 0000Z 70 KT 80 MPH
120 hour 05/27 0000Z 60 KT 70 MPH...inland

5-day track forecast



Figure 4. My 5-day forecast track for TD Two-E.

Updated: 5:15 AM GMT on May 22, 2012

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Tropical weather analysis - May 21, 2012

By: KoritheMan, 6:09 AM GMT on May 21, 2012

Alberto

Alberto is hardly a threat, and continues off the coast of Georgia as a minimal tropical storm. As of the latest NHC advisory, the following information was posted on the storm:

Wind: 40 mph, with higher gusts
Location: 30.5°N 80.1°W
Movement: S at 5 mph
Pressure: 1007 mb
Category: Tropical storm (Saffir-Simpson Hurricane Scale)

Alberto is getting ready to recurve, as satellite and radar data suggest that the tropical cyclone is moving south. Presumably, this is in response to the beginnings of the anticipated deterioration of the blocking pattern that is currently draped across the eastern United States. While it's true that I had forecast a landfall, I was at least fortunate enough to be correct that the storm would make it perilously close to the coast before recurving.

The cyclone peaked shortly after formation, and has been on a slow decline ever since. Convection is limited to the eastern semicircle due to westerly shear. And indeed, what convection exists is fairly shallow. With the shear forecast to follow Alberto on its seaward trek, reintensification later in the period seems unlikely despite slowly warming sea surface temperatures.



Figure 1. Latest infrared satellite image of Tropical Storm Alberto, courtesy of NOAA's Satellite Services Division (SSD).

In the meantime, the cyclone can be expected to slowly weaken due to the extremely subsident airmass in which it is embedded. It is possible that if current convective trends persist, Alberto will weaken to a depression by morning. In fact, the cyclone could weaken even faster than what I have indicated below. Most of the models lose the circulation in about three days, and Alberto is forecast to be extratropical by that time.

All coastal watches were discontinued earlier today.

5-day intensity forecast

Initial 05/21 0300Z 35 KT 40 MPH
12 hour 05/21 1200Z 30 KT 35 MPH
24 hour 05/22 0000Z 30 KT 35 MPH
36 hour 05/22 1200Z 25 KT 30 MPH
48 hour 05/23 0000Z 25 KT 30 MPH
72 hour 05/24 0000Z 25 KT 30 MPH...extratropical
96 hour 05/25 0000Z...dissipated

Invest 92E

The area of low pressure we have been tracking across the eastern Pacific for several days has finally developed enough persistent thunderstorm activity to be considered a tropical depression. As of the most recent NHC advisory, the following was posted:

Wind: 35 mph, with higher gusts
Location: 9.3°N 99.6°W
Movement: WNW at 5 mph
Pressure: 1005 mb
Category: Tropical depression (Saffir-Simpson Hurricane Scale)

There isn't much convection over the center, as easterly shear continues to inhibit conglomeration of the shower activity. Instead, satellite photos portray a sheared system, with most of the thunderstorms confined downstream from the center, or in simpler terms, the western quadrant.



Figure 2. Latest infrared satellite image of Tropical Depression Two-E, courtesy of NOAA's Satellite Services Division (SSD).

A large ridge over the western Caribbean has been the catalyst with regards to the shear over the system. Careful examination of water vapor imagery shows that this ridge hasn't really moved much, and shear is expected to remain in at least the 15 kt range through 24 hours. This should at least slow intensification, given the system's relatively slow movement. Thereafter, upper-level winds are forecast to slowly become more anticyclonic as a broad 200 mb ridge builds over the cyclone. This should allow a greater degree of intensification beyond that time. Later in the period, the system is forecast to be moving across cooler waters. Although these waters will still be warm, they are cool relative to what the cyclone is experiencing now. In addition, oceanic heat content degrees markedly north of 15N. This should at least slow intensification. Although the NHC mentions stronger shear afflicting the storm by that time, I see mostly southeasterlies in the GFS, which is not conducive to weakening of a storm moving northward. In the event the system develops a well-defined inner wind core and moves underneath the warm ridge, rapid intensification is possible over the very warm eastern Pacific waters, which are warmer than normal this year due to the emerging El Nino. Of course, we have little skill in predicting these episodes, but the bottom line is that southwest Mexico should prepare for a hurricane.

A more primary ridge is building over the central United States in the wake of an upper-level trough/attendant cold front, the same one that will recurve Alberto. Large scale guidance suggests this should continue around Wednesday evening, when the cyclone is forecast to slowly get picked up by a developing trough off the west coast. This trough is forecast to be of particularly large amplitude, so it should prove sufficient to recurve the system. The GFDL and HWRF are faster, but like the NHC, I have ignored those for now. The system is forecast to be just off the coast in five days. However, there are three possible scenarios I see for this system as it approaches the coast in the long-range: a) the system moves inland a little faster than anticipated, b) it moves as forecast, or c) it briefly moves inland, then moves westward back over water due to difficult to predict local wind patterns downslope from the mountains.

Whatever the case, interests in and along the southwest coast of Mexico from Puerto Vallarta to Manzanillo should closely monitor the progress of this tropical cyclone, which is expected to strengthen.

5-day intensity forecast

Initial 05/21 0300Z 30 KT 35 MPH
12 hour 05/22 1200Z 35 KT 40 MPH
24 hour 05/23 0000Z 40 KT 45 MPH
36 hour 05/23 1200Z 50 KT 60 MPH
48 hour 05/24 0000Z 60 KT 70 MPH
72 hour 05/25 0000Z 75 KT 85 MPH
96 hour 05/26 0000Z 80 KT 90 MPH
120 hour 05/27 0000Z 85 KT 100 MPH

Hurricane Flood

Updated: 9:17 AM GMT on May 21, 2012

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Tropical weather analysis - May 19, 2012

By: KoritheMan, 1:26 AM GMT on May 20, 2012

Alberto

Here's one I didn't anticipate. Tropical Storm Alberto formed off the coast of South Carolina today. As of the most recent NHC advisory, the following was posted:

Wind: 50 mph, higher gusts
Location: 31.8°N 78.5°W
Movement: SW at 6 mph
Pressure: 998 mb
Category: Tropical storm (Saffir-Simpson Hurricane Scale)

The center is difficult a bit difficult to locate, but based on a healthy slew of radar and satellite fixes, is estimated to be within the southern side of the convection. Assuming I'm correct, the cyclone is not as disheveled as it looks. However, disorganized systems like Alberto often contain mid-level circulations that are displaced from the surface circulations.



Figure 1. Latest infrared satellite image of Tropical Storm Alberto, courtesy of NOAA's Satellite Services Division (SSD).

Alberto's future track is highly uncertain, complicated by a well-defined upper low between Virginia and Bermuda. This system extends all the way down to 850 mb, so its influence on Alberto can be expected to be rather large. However, the global models unanimously move this low into eastern North Carolina and/or southern Virginia in about a day or so, and current water vapor images would seem to support this. Alberto is trapped in a col region between a large ridge over the Ohio Valley, and the aforementioned upper low. The combination of these features, and a shortwave trough over the central United States should cause a gradual bend of the storm to the north, and eventually northeast.

Large scale guidance is in decent agreement about this, though it really depends on exactly where Alberto's center is. If it is indeed within the recent burst of convection on the south side as I suspect it is, a landfall on the mainland is virtually inevitable. If the center is farther north, the storm might merely skirt the coast. I anticipate a landfall along the South Carolina/North Carolina border tomorrow afternoon. The timing and placement of landfall will also weigh heavily on the influence of the aforementioned upper low, which is forecast to fill as it moves inland, and also the progression of the relatively flat trough to the west.

After landfall, Alberto should move back out into the Atlantic. Passage over cold waters north of the North Carolina coast should preclude reintensification. Alberto is expected to become extratropical in about four days.

Given the complexities of the synoptic steering pattern, this is a rather low-confidence forecast.

5-day intensity forecast

Initial 05/19 0300Z 45 KT 50 MPH
12 hour 05/20 1200Z 45 KT 50 MPH
24 hour 05/21 0000Z 50 KT 60 MPH
36 hour 05/21 1200Z 50 KT 60 MPH
48 hour 05/22 0000Z 45 KT 50 MPH...inland
72 hour 05/23 0000Z 40 KT 45 MPH...over water
96 hour 05/24 0000Z 35 KT 40 MPH...extratropical
120 hour 05/25 0000Z...dissipated

Watches and warnings

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

A TROPICAL STORM WATCH HAS BEEN ISSUED FOR THE COAST OF SOUTH
CAROLINA FROM THE SAVANNAH RIVER TO SOUTH SANTEE RIVER.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* SAVANNAH RIVER TO SOUTH SANTEE RIVER SOUTH CAROLINA

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

COASTAL INTERESTS ELSEWHERE FROM GEORGIA THROUGH THE OUTER BANKS OF
NORTH CAROLINA SHOULD MONITOR THE PROGRESS OF ALBERTO.

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

Invest 92E

The tropical disturbance we have been tracking in the eastern Pacific over the last several days is a little better organized today, but I use that term rather loosely. While convection is slowly regenerating, this activitty is poorly-organized, and the overall circulation remains broad and ill-defined.



Figure 2. Latest infrared satellite image of Invest 92E, courtesy of NOAA's Satellite Services Division (SSD).

Some modest easterly shear continues to afflict the system, but these winds are forecast to decrease over the next day or two. The largest impediment to development continues to be the very slow movement of the disturbance, which is putting it closer to the axis of a large ridge over the western Caribbean. It appears that this feature has been the primary cause of the shear the system has encountered over the last couple of days.

The large scale steering pattern for 92E remains in the hands of a developing storm system over the western Pacific. The upper low attendant to this feature that is expected to bring the trough into the US is located in the open Pacific between the Hawaiian Islands and the coast of Oregon. Based on the placement and speed of this feature, the trough appears to be pretty much on schedule, so a long-range threat to Mexico is still warranted.

The models, naturally, still disagree on the specifics -- namely the timing and amplitude of the trough. The CMC and NOGAPS show a slightly weaker trough and are thus farther west, taking about 12-24 hours more to recurve 92E into southwest Mexico. The GFS and ECMWF, typically more reliable, show a more clear-cut path into central Mexico, and landfall on Friday. It should be noted that the 12z run of the ECMWF actually sends the storm back offshore on Saturday beneath a developing mid-level ridge. This is likely a reflection of the lower tropospheric steering, as model height fields still show a definitive mid-level weakness in the central United States ridge during this time. And because the system is expected to be strong by then, it is unlikely to be steered by the lower- tropospheric flow.

Interests along the coast of Mexico from Puerto Vallarta to Acapulco should continue to monitor the progress of this disturbance.

Probability of genesis within the next 48 hours: 30%

Hurricane Flood

Updated: 5:40 AM GMT on May 20, 2012

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Tropical weather analysis - May 18, 2012

By: KoritheMan, 2:50 AM GMT on May 19, 2012

Aletta

Aletta is finally showing signs of succumbing to the shear. The storm is poorly-organized on satellite imagery, with the low-level center completely exposed well to the west of a small area of convection. As of the latest NHC advisory, the following information was posted:

Wind: 30 mph, with higher gusts
Location: 14.5°N 113.2°W
Movement: NE at 3 mph
Pressure: 1006 mb
Category: Tropical depression (Saffir-Simpson Hurricane Scale)

There is no doubt that Aletta looks worse than 24 hours ago, and satellite estimates have plummeted accordingly. The cyclone is likely to decay to a remnant low very soon, probably in about six hours. It is possible that the cyclone is already a remnant low, and I will verify this in post-season analysis.



Figure 1. Latest infrared satellite image of Tropical Depression Aletta, courtesy of NOAA's Satellite Services Division (SSD).

Large scale imagery and model guidance indicates that the current shearing environment will persist. As Aletta turns southward, the upper flow will veer southeasterly, perhaps more detrimental than the ongoing southwesterly regime, since such a path would move the cyclone directly into the shear. Models are unanimous in absorbing Aletta into a larger cyclonic circulation to the east.

Satellite imagery suggests that Aletta is turning eastward. A sharp southward bend is expected in the track tomorrow, as the cyclone/remnant low slowly becomes entrained into the circulation associated with Invest 92E.

5-day intensity forecast

Initial 05/18 2100Z 30 KT 35 MPH
12 hour 05/19 0600Z 25 KT 30 MPH...post-tropical/remnant low
24 hour 05/20 1800Z 25 KT 30 MPH...post-tropical/remnant low
36 hour 05/21 0600Z 20 KT 25 MPH...post-tropical/remnant low
48 hour 05/22 1800Z 20 KT 25 MPH...post-tropical/remnant low
72 hour 05/23...absorbed by developing tropical cyclone

Invest 92E

In an interesting turn of events, Invest 92E has become considerably less organized today. The system consists of an elongated and shapeless band of convection extending westward for over 100 miles. I'm not going to pretend the center is easy to locate. Presumably, it is under the southern edge of the convection near 11.2N 100.3W, based on low-cloud motions gleaned from earlier visible imagery.



Figure 2. Latest infrared satellite image of Invest 92E, courtesy of NOAA's Satellite Services Division (SSD).

Courtesy of a large ridge over the western Caribbean, 92E is under about 20 kt of southeasterly shear, and this is strongly supported by satellite trends. The system has an impressive equatorial outflow channel due to this shear, and thus it may not die completely. The shear is forecast to abate in about 24 hours, although the environment will still not quite be anticyclonic. Most of the models respond by making this system a hurricane in about five days. I usually don't agree well with model intensity forecasts, since we know so very little about tropical cyclone intensification procedures, but in this case they could turn out to be correct.

Water vapor imagery shows a strong upper-level trough approaching the central United States. The upper low supporting this front is currently moving across western Utah. With a predominant northwesterly flow in place, said low should move southeastward for at least a day, dragging the cold front with it. Given the amplitude of this front, weak southwesterly flow is likely to linger as far south as the Gulf of Tehauntepec. This should prevent the storm from making too much westward progress. However, this trough is arriving sooner than the models were predicting yesterday, which may throw a wrench into my track predictions by allowing the storm to move more westerly by late Sunday into Monday as the high pressure area to the north of the low briefly rebuilds in the wake of the trough.

By Monday, another trough is forecast to enter the western United States. The models are unanimous that this trough will have a rather large amplitude, though they disagree on the exact placement of it. The GFS and ECMWF are farther north and slower, with the system still offshore next Friday, while the other models are a bit farther south and somewhat quicker. The 18z GFS looks a little suspect, even with the more northward placement of the trough, as a then hurricane is still well offshore. This is probably because that model initializes and develops a spurious vortex to the east of Invest 92E. Westerly flow associated with that feature (then tropical cyclone) attempts to grab the storm and scoot it east and ends up losing out -- but not without slowing the system's progress. Smoothing out the bogus vortex lends to a similar timing and position to the ECMWF.

It appears that 92E will be with us for awhile. One thing I'm confident of is that this system poses a long-range threat to the southwest coast of Mexico, and interests there should monitor it. I suppose it's worth noting that the NOGAPS shows a much more gentle recurvature, toward southern Baja. While none of the other models agree with this, depending on the evolution of the western US trough, it's a faint possibility.

Most of the models aren't developing this system until around Monday evening.

Probability of genesis within the next 48 hours: 20%

Atlantic subtropical development less likely

While the models are still hinting that the large baroclinic zone off the southeast United States coast could lead to the development of a weak surface low, they are less enthusiastic today than in previous runs. This area still needs to be watched, but I am not impressed. Perhaps some increased instability will overspread this region, however.

Hurricane Flood

Updated: 2:53 AM GMT on May 19, 2012

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Tropical weather analysis - May 17, 2012

By: KoritheMan, 5:16 AM GMT on May 18, 2012

Aletta

Aletta weakened to a tropical depression in the wee hours of Thursday morning. As of the latest NHC advisory, here is the information on this system:

Wind: 35 mph, with higher gusts
Location: 13.6°N 114.3°W
Movement: NNE at 6 mph
Pressure: 1006 mb
Category: Tropical depression (Saffir-Simpson Hurricane Scale)

A bursting-type pattern of convection continues, but remains west of the low-level center. Although this convection when it erupts is fairly cold, tropical cyclones, as a general rule, do not strengthen amidst bursting patterns. It is a bit of a mystery to me why the convection is confined west of the center as opposed to east. One would think that in an environment characterized by southwesterly shear, an inverse relationship would apply. Careful analysis of water vapor imagery, corroborated by CIMSS mid- to upper-level wind data, shows no evidence of easterly shear beneath the outflow layer. Satellite imagery does reveal arc clouds emanating from the eastern quadrant of the depression, which is usually a sign of dry air, so maybe that's it. But in the end I suppose, it's best not to read too deeply into a triviality that will ultimately not alter Aletta's fate.



Figure 1. Latest infrared satellite image of Tropical Depression Aletta, courtesy of NOAA's Satellite Services Division (SSD).

A small weakness prevails north of the storm toward the Mexican coast in association with a weak frontal trough. Although this trough was apparently strong enough to recurve Aletta, its ultimate demise will be met not at the hands of cold water and wind shear, but at eventual absorption into a larger tropical disturbance to the east; large scale imagery suggests that this disturbance is beginning to dominate the low-level flow in the vicinity of Aletta, and this evolution should absorb the storm by Monday. The global models are in excellent agreement with this scenario.

Aletta should weaken in the interim, and degenerate into a remnant low in about 24 hours. An SSMI overpass near 0z was kind enough to catch the important half of the circulation -- i.e. the center -- and a comparative analysis of the mid- and upper-level circulations suggests a vertical decoupling, courtesy of the southwesterly shear impacting the tropical cyclone, which finally materialized as the GFS said it would. To add insult to injury, a large expanse of dry air lies to the west of the storm, associated with the stable stratocumulus cloud deck intrinsic to this portion of the Pacific west of 115W.

The models are discrepant on exactly where the storm will move in such a weak steering environment, but broadly agree on an eventual turn to the southeast or east-southeast as it becomes embedded within the environmental westerly flow in the lower troposphere being created by Invest 92E. I have done what seems appropriate, and have taken the GFS forecast, which seems supported in light of current synoptic trends. However, I'm sure Aletta will move in fits and wobbles until absorption.

5-day intensity forecast

Initial 05/17 0300Z 30 KT 35 MPH
12 hour 05/17 1200Z 25 KT 30 MPH
24 hour 05/18 0000Z 25 KT 30 MPH...post-tropical/remnant low
36 hour 05/19 1200Z 20 KT 25 MPH...post-tropical/remnant low
48 hour 05/20 0000Z 20 KT 25 MPH...post-tropical/remnant low
72 hour 05/21 0000Z 20 KT 25 MPH...post-tropical/remnant low
96 hour 05/22 0000Z...absorbed by developing tropical cyclone

Invest 92E

Shower activity in association with a broad area of low pressure centered several hundred miles south of Acapulco has become a little better organized, with a recent burst of very cold cloud tops exceeding -80C in some locales. The center is difficult to locate using nighttime imagery, but earlier microwave data and careful analysis of recent satellite visuals place it just inside the eastern edge of the convective canopy.



Figure 2. Latest infrared satellite image of Invest 92E, courtesy of NOAA's Satellite Services Division (SSD).

Upper-level wind analysis from University of Wisconsin CIMSS says 92E is experiencing 20 kt of easterly shear, and current satellite trends authenticate that. However, upper-level winds are forecast to become more favorable in the path of the system, especially beyond 24 hours. Pretty much all the global models turn this into a hurricane, and it appears pretty likely that this low will become the next named storm. If so, it would be named 'Bud'.

This disturbance is expected to remain virtually stationary until Sunday, when a trough over the central United States if forecast to be replaced by a ridge. This should steer the system on a gentle westward track until the next trough arrives on Tuesday. The amplitude of this trough is fairly impressive in the global model forecast fields, and if true, would be sufficient to recurve it toward the Mexican coast by midweek. The models have come into better agreement on the evolution of the synoptic pattern in today's cycles, which increases confidence in an eventual threat to the Mexican coast, especially from Puerto Vallarta eastward to Manzanillo. It is not uncommon for this portion of the coast to receive a direct hit from a tropical cyclone, and interests across the entire coastline, as a course of least regret, should closely follow the progress of this disturbance.

Probability of genesis within the next 48 hours: 60%

Atlantic (sub?)tropical development still possible

The global models are continuing to sing their tune of enthusiasm in regards to developing a subtropical or tropical entity -- or cyclone -- off the southeast United States coast in about three days. Given the harsh environmental westerlies in this area, any development here would probably be subtropical. However, the GFS indicates that the system could find a small hole of lower shear off the coast of the Carolinas, which would allow it to develop tropical characteristics. Preexisting cloudiness is already there, so we will need to watch this area carefully over the next several days.

Some of the models now suggest the system could loop back around to the west as the trough fails to shoot it into the westerlies.

Hurricane Flood

Updated: 5:28 AM GMT on May 18, 2012

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Tropical weather analysis - May 16, 2012

By: KoritheMan, 4:54 AM GMT on May 17, 2012

Aletta

Tropical Storm Aletta is holding its intensity over the open Pacific. As of the latest NHC advisory, the following was posted on the storm:

Wind: 40 mph, with higher gusts
Location: 11.5°N 114.3°W
Movement: W at 9 mph
Pressure: 1004 mb
Category: Tropical storm (Saffir-Simpson Hurricane Scale)

Some cold-topped convection has formed just north of the low-level center, and Aletta hangs on as a tropical storm for a little longer. One possible reason that Aletta has not weakened as quickly as forecast could be due to a lack of southwesterly shear, despite being consistently forecast by the GFS model since the cyclone's inception.



Figure 1. Latest infrared satellite image of Tropical Storm Aletta, courtesy of NOAA's Satellite Services Division (SSD).

Nonetheless, the cloud pattern is gradually deteriorating, brief convective upswings like the ongoing one notwithstanding. Water vapor imagery near the storm shows that it is enveloped by a large area of dry air on the subsident side of a mid-level ridge.

Water vapor imagery indicates that Aletta is nearing the western periphery of the ridge, and should soon turn poleward. Ordinarily, I would predict weakening systems like Aletta to move westward instead, but CIMSS analysis shows that this weakness extends as far down as 850 mb. However, it will probably still be another 12 hours before Aletta makes the turn, and about another 24 before she begins to move northeast. By Saturday, the cyclone is expected to turn eastward, then east-southeast, trapped amidst large-scale westerly flow associated with Invest 91E, which is forecast by the global models to become a tropical cyclone. This seems supported by current organization trends.

The GFS wants to keep the shear over Aletta a little bit less over the next 24-48 hours, and this is certainly supported by water vapor imagery. Since there are still no real signs of shear yet, I feel Aletta will weaken a bit slower than the global models are indicating, at least for the first 24 hours. Thereafter, the cyclone should encounter a sharp sea surface temperature gradient west of 115W, and begin to weaken more rapidly. This process will be further hastened by the very dry airmass lying west of the 26C isotherm. Given that Aletta will only be skirting said gradient, rapid dissipation is not expected, especially since weak storms like this one tend to survive better in cooler waters than stronger ones. Instead, the cyclone will likely hang on as a lingering tropical depression while gradually being entrained into the westerly monsoonal flow associated with 91E.

5-day intensity forecast

Initial 05/17 0300Z 35 KT 40 MPH
12 hour 05/17 1200Z 35 KT 40 MPH
24 hour 05/18 0000Z 30 KT 35 MPH
36 hour 05/18 1200Z 30 KT 35 MPH
48 hour 05/19 0000Z 25 KT 30 MPH
72 hour 05/20 0000Z 25 KT 30 MPH...post-tropical/remnant low
96 hour 05/21 0000Z 25 KT 30 MPH...post-tropical/remnant low
120 hour 05/22 0000Z...absorbed by developing tropical cyclone

Invest 91E

A large tropical disturbance is located about 500 miles south of Acapulco. A small area of convection lies just north of the center, but the overall cloud pattern is poorly-organized. A poleward outflow channel has developed to the north, possibly in response to a mid- to upper-level low over central Louisiana, and its associated jet maximum over the Gulf of Mexico.



Figure 2. Latest infrared satellite image of Invest 91E, courtesy of NOAA's Satellite Services Division (SSD).

Upper-level winds appear favorable for additional development, but I must emphasize that the large size of this disturbance may limit the potential for rapid intensification in the short-term. Long term, as the system picks up speed and establishes a solid inner core, a greater degree of intensification is possible. This system has the potential to become the Eastern Pacific's first hurricane.

The future course of this disturbance is still up for speculation. The models agree on a trough moving across the central United States on Saturday. This trough is then forecast to deamplify and be replaced by a more zonal regime. This could deflect the storm to the west. Another, more potent trough, is forecast to enter the western United States on Monday. It is this secondary trough that the models suggest could recurve the system toward mainland Mexico. Recurvature depends entirely on how far west the system gets before the arrival of the second trough, a scenario impossible to verify. The GFS and ECMWF, both typically reliable, show a rather weak ridge in the wake of the first trough, as southwesterly flow lingers over the region. An upper low moving into western Colorado could help drag the trough currently over Wyoming southward, assisting in keeping a prevailing weakness over the central United States.

Given this, and the usual reliability of the aforementioned group, there is a decent chance of 91E eventually impacting some portion of the Mexican coast. However, since the other models, reliable in their own right, insist that 91E will veer away from land, I can't simply ignore that, either. As a course of least regret, I will forecast a slow northwestward motion for the next three days, followed by west-northwest until the next trough builds back in, at which point the system is expected to turn back to the northwest. Needless to say, this is a low-confidence forecast.

Interests along the entire coast of Mexico should follow the progress of this disturbance.

Probability of genesis within the next 48 hours: 40%

Elsewhere

Atlantic development is looking less likely, especially in the Caribbean. However, there is still weak support for a brief subtropical storm to form off the southeast United States coast. Such a system would move northeastward away from the mainland, embedded within the prevailing mid-latitude westerly flow.

Hurricane Flood

Updated: 5:03 AM GMT on May 17, 2012

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Tropical weather analysis - May 15, 2012

By: KoritheMan, 8:45 PM GMT on May 15, 2012

Aletta

Tropical Storm Aletta was named overnight. As of the just released advisory from the hurricane center, the following was posted:

Wind: 45 mph, with higher gusts
Location: 11.2°N 110.4°W
Movement: W at 10 mph
Pressure: 1003 mb
Category: Tropical storm (Saffir-Simpson Hurricane Scale)

The center remains just embedded within the of the ball of the central convection, which retains cloud top temperatures of about -80C. The cloud pattern is a little better organized than it was yesterday, with more curvature to the associated convection. The system is still undergoing easterly shear, as evidenced by the outflow pattern, where the cirrus are emanating primarily from the western quadrant.
Dry air lies just to the west, but this is not adversely affecting Aletta at this time.



Figure 1. Latest visible satellite image of Tropical Storm Aletta, courtesy of NOAA's Satellite Services Division (SSD).

Water vapor imagery shows that a weakness lies to the north of the tropical storm, over the Gulf of California and far western Mexico. Kudos to the global models, who have consistently predicted this. While I am still not calling for this to recurve Aletta, most of the global models express disagreement, with a large trough forecast to amplify to the west of the tropical cyclone. The purported weakness extends all the way down to at least 850 mb within the model forecast fields, so if this were to verify, Aletta would almost certainly feel some poleward tug. However, the cyclone is likely to slow significantly by Friday as it becomes embedded within a weak southwesterly steering regime, possibly a little sooner. It appears that this weakness has been moving Aletta a little more northward, as the storm is off by about 20 miles from the 0z forecast point.

Water vapor and CIMSS imagery shows that Aletta is headed toward a region of strong southwesterly shear. This should begin to weaken the storm by tomorrow. Indeed, the western semicircle is already being affected by this shear, with the cirrus no longer advancing westward. Also, since I expect the storm to move a bit more northerly now, this will put it closer to cooler waters that lie along 115W.

The storm still has a chance to intensify a little more before the shear sets in.

5-day intensity forecast

Initial 15/2100Z 40 KT 45 MPH
12 hour 16/0600Z 45 KT 50 MPH
24 hour 16/1800Z 40 KT 45 MPH
36 hour 17/0600Z 35 KT 40 MPH
48 hour 17/1800Z 30 KT 35 MPH
72 hour 18/1800Z 25 KT 30 MPH...remnant low
96 hour 19/1800Z 25 KT 30 MPH...remnant low
120 hour 20/1800Z...dissipated

Elsewhere

An area of disturbed weather has developed in the Gulf of Tehauntepec. Environmental conditions appear conducive for slow development of the disturbance as it moves west to west-northwest, although its large size may inhibit rapid development in the short-term.

Probability of development in 48 hours: 10%

The GFS continues to predict a western Caribbean tropical storm, and is a little more aggressive today. This system is now within the realm of one week, so it needs to be watched. I still don't think this system will amount to much, though, especially if pre-91E strengthens quicker than anticipated.

Hurricane Flood

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Tropical weather analysis - May 14, 2012

By: KoritheMan, 11:32 PM GMT on May 14, 2012

Tropical Depression One-E

The first tropical depression of the season has formed, albeit a day early. It is rather unusual to get a tropical cyclone prior to the official start of the season. As far as we know, there have only been two tropical cyclones that have formed before May 15: Hurricane Alma in 1990, and an unnamed tropical storm in May of 1996. As of the latest official NHC advisory, here are the coordinates on this strengthening system:

Wind: 35 mph, with higher gusts
Location: 10.0°N 107.3°W
Movement: W at 8 mph
Pressure: 1006 mb
Category: Tropical depression (Saffir-Simpson Hurricane Scale)

Visible satellite pictures reveal that the low-level center may be moving closer to the deep convection, and the system is very likely already a tropical storm. The tropical cyclone is battling southeasterly shear as evidenced by the restricted outflow to the east, but this has not permeated the core yet. Upper-level winds appear favorable for the system to become a moderate tropical storm before becoming less favorable by Tuesday afternoon.



Figure 1. Latest infrared satellite image of Tropical Depression One-E, courtesy of NOAA's Satellite Services Division (SSD).

Water vapor imagery shows the ridge building westward ahead of the tropical cyclone. This synoptic evolution favors a continued westward motion with an increase in forward speed, although model guidance is unanimous in significantly slowing the system beyond 72 hours in response to developing cyclonic flow to the west, associated with a trough, and cyclonic flow to the east, associated with a possible tropical cyclone in the Gulf of Tehauntepec.

The GFDL and HWRF still turn the storm toward Baja, but these models are clearly overdoing the storm's response to the anomalous southwesterly flow forecast to linger in the vicinity of Baja by midweek. In addition to that, these models almost always seem to exhibit a poleward bias for Eastern Pacific systems. I fail to see why the storm will be that deep, and the ridge is stronger than what some of the models are indicating, so my forecast track remains along the southern edge of the guidance, in best agreement with the 12z run of the GFS.

This system should dissipate in about four days.

Elsewhere

Global model guidance continues to insist on another tropical cyclone developing behind TD One-E in about five to six days. This occurs as a large surge of monsoonal moisture manifests across the western Caribbean and adjacent eastern Pacific. This moisture is likely attributable to the upward pulse of the MJO moving into that area of the world. The synoptic pattern, with a 500 mb weakness in the Gulf of Mexico, favors an eventual turn to the Mexican coast, although long-range prognostications like this one are highly speculative. Regardless, this system should move slowly enough and remain in close enough proximity to the coast to deliver several days of locally heavy rains, as well as high surf along coastal areas.

On the Atlantic side of things, the GFS continues to forecast the development of a tropical storm in the western Caribbean. While theoretically this is possible given the large-scale pattern in this region (lower pressures in the western Caribbean and Gulf of Mexico downstream higher heights across the midwest and Great Lakes), I think there is simply too much energy in the Pacific for this storm to have much room to develop. Additionally, the forecast point of origin within this model is very close to Central America, another factor that could inhibit development. It is pretty unusual to get a named storm in May, much less one forming side by side another tropical cyclone. However, heavy rainfall could eventually overspread portions of south Florida, bringing welcome rains.

The models have also backed off in developing a tropical storm off the eastern seaboard. Conceivably, this would occur with a dying cold front that moves into the western Atlantic in about five days. At the very least, it is possible that a weak area of low pressure could form along the tail end of the then diffuse front. Such a system would move out to sea amidst southwesterly environmental steering flow.

Hurricane Flood

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Tropical weather analysis - May 14, 2012

By: KoritheMan, 6:45 AM GMT on May 14, 2012

Invest 92L

A non-tropical area of low pressure centered in the far eastern Atlantic about 470 miles south-southwest of the southern Azores is no longer a threat to develop. The system lost much of its thunderstorm activity earlier in the day, and, the current resurgence notwithstanding, this low has already peaked, and will slowly fizzle as the cyclonic circulation that's sitting over it moves away, taking with it the system's upper support.

Probability of genesis within the next 48 hours: 10%

Invest 90E

The Pacific, on the other hand, remains active, with an area of disturbed weather centered about 600 miles south-southwest of Manzanillo continuing to generate showers and thunderstorms. Convection diminished earlier in the day, possibly as a result of dry air intrusion, but is on the rebound again. Low cloud motions indicate that the circulation associated with this disturbance is gradually gaining definition, and with favorable upper-level winds in the path of this system for at least the next day or so, this low has the potential to become a tropical depression.



Figure 1. Latest infrared satellite image of Invest 90E, courtesy of NOAA's Satellite Services Division (SSD).

The upper flow over the system is not anticyclonic, but is at least diffluent enough to allow strengthening. This theme will soon change, as the GFS forecasts the system to run into a wall of westerly shear by Tuesday afternoon. This shear appears to be attributable to the persistent mid-oceanic trough which normally dominates the central Pacific. Incidentally, this is also why Hawaii generally remains free of tropical cyclones.

Water vapor and large scale imagery indicates that the Pacific ridge is building westward ahead of 90E. With no obvious reasons why this ridge should weaken, this pattern favors a west-northwest to westward motion over the next five days. By Tuesday evening, weak southwesterly flow is forecast to reestablish over Baja California, so that enough of a weakness will be present in the ridge to nudge the system unclimatologically slowly. It's worth noting that the GFDL still turns 90E toward Baja by midweek, but this is predicated on a deeper system responding more fully to the trough draped across that area in the models. All of the models show this weakness, but most don't respond to it since they keep 90E a relatively weak system. Given the narrow window of opportunity in which the system has to strengthen, I tend to agree with this.

The global models lose the circulation in about five days, but this could occur sooner given the magnitude of westerly shear the system is forecast to encounter.

This low is unlikely to become anything more than a weak tropical storm.

Probability of genesis within the next 48 hours: 60%

Elsewhere

The global models continue to insist on another tropical cyclone forming to the east of Invest 90E, in the Gulf of Tehuantepec. This is forecast to occur in about five days. Satellite imagery and MIMIC-TPW imagery from CIMSS indicates a large surge of moisture has manifested in this region. There is not enough evidence to justify labeling the area of rotation in the southwestern Caribbean a tropical wave. Either way, a large area of rainfall and embedded thunderstorms stretches across the Caribbean and far eastern Pacific from about 7-8°N 75°W westward to about 100°W, and the eastern end of this activity could serve as the instigator for a tropical storm.

A large monsoonal circulation over this portion of the world is typical this time of year, and is often times how an early-season tropical storm gets going. Some of the models are responding to this pattern by hinting that the western Caribbean will see development as well. Given current satellite trends, and the forecast of a northeastward-moving tropical storm in the GFS, it is possible that a situation similar to Alma/Arthur in 2008 will transpire, leading to the formation of Alberto in the western Caribbean. It is also possible that this will be a separate entity. Regardless, both areas will need to be watched carefully, as the potential does exist for tropical storm formation in this region.

The models are depicting the possibility of a weak tropical cyclone developing off the southeast or mid-Atlantic coast in about four days. The weak cold front/trough currently over the southern United States is forecast to deamplify and become quasi-stationary over the eastern seaboard during this time. With strong upper-level shear, development isn't terribly likely, but the quick forward motion of the system as it accelerates into the westerlies could allow it to outrun the shear.

Hurricane Flood

Updated: 7:43 AM GMT on May 14, 2012

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Tropical weather analysis - May 13, 2012

By: KoritheMan, 6:18 AM GMT on May 13, 2012

Invest 92L

This just keeps getting better and better. In a surprising turn of events, the Atlantic has decided to spin something up, as well. A non-tropical gale area ("92L") has developed about 400 miles southwest of the southern Azores. Sometimes it's easy to miss these small subtropical entities in light of other, more flagrant observations. Satellite and scatterometer data indicate that this system possesses a large, well-defined circulation at the surface. In addition, this low is already producing winds to tropical storm force, mainly in squalls to the east of the center. These winds are probably at least partially attributable to a steep pressure gradient between the low and the Bermuda/Azores ridge, whose axis lies to north.



Figure 1. Latest infrared satellite image of Invest 92L, courtesy of NOAA's Satellite Services Division (SSD).

Synoptic data indicates that 92L is embedded within a large cyclonic circulation over the north Atlantic. This circulation extends all the way down to at least 850 mb. In theory, this would tend to cap development potential, but 92L is not a tropical entity. Water vapor and CIMSS vorticity imagery shows that 92L is sitting beneath an upper low that encompasses this cyclonic circulation. This is promoting a low shear environment, hence the relative symmetry of the cloud pattern. The associated shower activity appears to be getting a little better organized in recent frames.

Sea surface temperature analyses from NOAA's AOML division shows 92L sitting right in the middle of cold waters, about 19C.



Figure 2. Atlantic sea surface temperatures (SSTs) as of May 11, 2012, courtesy of NOAA's AOML research division.

Long-term satellite loops show that 92L has barely moved, except for perhaps 30 miles to the north. This is reflective of the weak steering regime which surrounds the storm. There is a wide diversity in the respective model tracks, between the westernmost GFDL which crawls the system northwest, and the easternmost GFS, which moves the system generally east-northeast. This kind of disagreement usually implies weak steering, so little movement of this disturbance is forecast for the next few days, save for perhaps a continued northward drift. More likely, overall motion will continue to be slow and erratic as 92L attempts to loop around the large cyclonic circulation in which it is embedded, only to get tugged back to the west by the subtropical ridge.

I hate forecasting these slow-moving storms. Fortunately, it appears that nature has seen fit to grant me a reprieve, as a positively-tilted upper trough currently stretching from the Bahamas to Atlantic Canada slowly amplifies over the next 48 hours. Unfortunately, it appears as if this trough will not be in a hurry to pick up 92L, and it will likely have to wait for reinforcements in the westerlies emanating from Quebec. Even then, recurvature will be painfully slow, and 92L could meander near the Azores for several days.

Any development from 92L will be subtropical.

Probability of genesis in the next 48 hours: 40%

Invest 90E

An area of disturbed weather continues about 550 miles west-southwest of Acapulco. The associated shower activity has become better organized during the day.

Nighttime imagery, particularly in light of the ongoing convective burst, has made finding a center rather difficult. My best estimate is 10.4°N 103.9°W, which is right in the middle of the convection. However, WindSat was unavailable, and ASCAT inconclusive, so the actual center could be anywhere within a half a degree north and west of where I have it. Undoubtedly, visible satellite images will shed some light in the morning. It should be noted that there appears to be a vorticity center northwest of the convective mass, and if that is correct, 90E is highly disorganized. My forecast is predicated on the assumption that the low-level center is in that convective ball.

The system is currently underneath a budding anticyclone, and the GFS forecasts this anticyclone will strengthen over the next 48 hours. That, combined with 29 to 30C SSTs which the system currently sits over, would tend to favor significant intensification. Thus, if current trends persist, I would expect a tropical depression sometime tomorrow. It is possible that a period of rapid intensification could ensue, but I am not willing to forecast this for two reasons: the first being that we have little skill in anticipating these events, and also because the system still lies close to the ITCZ. If rapid intensification does happen, it is not out of the question that this low could come close to hurricane strength.

After 48 hours, the system loses its upper-level anticyclone as it approaches the mid-oceanic trough characteristic of the central Pacific waters. By Tuesday, the system will be heading into very strong westerly shear, which should retard the development process and initiate weakening. It should be noted that should the system stay farther south, it would likely avoid the worst of the shear, and would survive longer due to warmer sea surface temperatures.

As the models predicted, a fast-moving upper low approaching 35N has lifted out, and is now approaching southern California. Consequently, the frontal zone that was attendant to this feature has lost its upper support, and is thus dissipating. This is shown nicely on water vapor imagery, where the middle- to upper-tropospheric flow is becoming more zonal. The sudden rebuilding of the Pacific ridge has prompted me to shift my forecast a little to the south of where it was yesterday. I anticipate a slow northwestward motion in the short-term, followed by west-northwest, then west with an increase in forward speed. The westward turn should occur in about 36 hours. Some of the models try to turn the system toward Baja in the long-range, but this is contingent on a vertically deep system. Nevertheless, there does appear to be some troughing in that area within the global model forecast fields around that time, so depending on the amplitude of this trough, this possibility will need to be assessed.

Most of the models lose the circulation in about five to six days.

Probability of genesis in the next 48 hours: 60%

Elsewhere

The global models, mostly the GFS and ECMWF -- you know, the important ones -- continue to forecast the possibility of a secondary tropical cyclone developing to the east of Invest 90E in about a week. This system is forecast to originate in the Gulf of Tehauntepec. However, given the large surge of monsoonal moisture likely to envelope the eastern Pacific/western Caribbean during this time, the potential certainly exists for a cyclone to spin up on the Atlantic side. Regardless, it appears that a large fetch of tropical moisture associated with a probable area of disturbed weather over this area of the world heralds heavy rainfall for south Florida. This region is under a severe drought, so any rains will be beneficial.

Also, I held off on mentioning this yesterday, but the GFS, and the ECMWF forecast that a cold front forecast to move off the eastern US next week could serve as the nucleus for a tropical storm. Such a storm would very likely move out to sea, well-embedded within the mid-latitude westerlies.

Hurricane Flood

Updated: 7:45 AM GMT on May 13, 2012

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Tropical weather analysis - May 11, 2012

By: KoritheMan, 4:19 AM GMT on May 12, 2012

Invest 90E

The Eastern Pacific hurricane season is right around the corner, but apparently, it wants to show signs of life early. A tropical disturbance has developed about 500 miles southwest of Acapulco, Mexico. The center of rotation of this disturbance is officially estimated at 8.9°N 104.7°W as of 21z. My fix is a bit farther north, closer to 10N 105W.



Figure 1. Latest infrared satellite image of Invest 90E, courtesy of RAMMB imagery from Colorado State University (CSU).

Whatever the case, this system definitely has that developing look to it. The biggest hurdle appears to be its slow movement, with little overall motion shown on satellite pictures over the last few hours. The result will be a binary interaction with the Intertropical Convergence Zone, which lies just to the south of the budding disturbance. This may try to interfere with development by limiting lower-level inflow. Although strong upper-level shear lies just to the west, as per CIMSS, this shear is clearly not reaching the system at this time. Although cloud tops are cold, there are no signs of organization yet.

Although strong upper-level winds lie in close proximity, water vapor imagery and objective steering analyses suggest that the environmental flow surrounding the system remains weak. Indeed, the synoptic pattern over this section of the Pacific currently resembles an Omega type blocking pattern, with 90E caught amidst that pattern. Since the system is pretty much quasi-stationary at this time, it remains effectively shielded from the dangerous southwesterlies which lie ahead. A very slow northwestward motion can be expected, in line with the models. Some slight acceleration will be possible over the ensuing 24-48 hours.

Water vapor imagery depicts a well-defined cold low centered far to the west of the system, near 30N 138W. Large scale models quickly evacuate this feature over the next 12-24 hours, leaving the weak cold front that currently trails the low to dissipate. The result will be an increase in ridging, which should turn the system westward with time. The models are split, so I have taken the middle road in calling for a slow west-northwest movement by Sunday with a gradual acceleration as the easterlies to the north of the system rebuild. This track is in good agreement with the 18z run of the BAMM. Eventually, the system should encounter cooler waters and dissipate. I do not currently anticipate a hurricane, but I have been wrong before, and the Eastern Pacific has been shown to produce strong hurricanes during this part of the year.

Should the system track north of where I think it will, its path would take it closer to strong upper-level westerlies, as well as cooler sea surface temperatures.

Probability of development into a tropical cyclone during the next 48 hours: 10%

Elsewhere

Elsewhere in the tropics, the global models, including the typically reliable GFS and ECMWF, forecast the development of a secondary tropical cyclone to the east of Invest 90E in about a week. Satellite imagery does show the beginnings of a manifestation of disorganized cloudiness in that area. This may be reinforced by a large, convectionless swirl moving across Panama and the extreme southwestern Caribbean. There is not enough evidence to say if this is a tropical wave, but given the time of year it's not impossible. In addition, the ITCZ is rather active in this area of the Pacific, and with the upward MJO forecast to move eastward, the potential certainly exists for two tropical cyclones.

Also, I'd like to point out that the models, mainly the GFS, have been pretty consistent in the long-range in developing a low pressure area -- and possible tropical cyclone -- somewhere in the western Caribbean in about 10 days. This is undoubtedly due to a large flux of instability associated with the upward pulse of the MJO. If any development were to occur this early in the year, climatology certainly favors that area. However, there are simply too many uncertainties at this time to justify anything beyond a mention. It's also worth noting that with El Nino coming on, the Pacific is warmer than normal, which would tend to keep the MJO around for longer. This could be why the models are developing Bud behind possible Aletta. Given the depiction of the former system within the models, any tropical cyclone would have a tough time getting going.

Regardless, it appears that a multi-day period of heavy rain is possible across south Florida in about 7 - 10 days, as a large conglomeration of moisture overspreads the western Caribbean. In addition, the western Atlantic ridge is forecast to erode with the passage of a weak cold front late next week, and the southerly flow associated with this feature could generate some shower activity over the state.

Hurricane Flood

Updated: 4:33 AM GMT on May 12, 2012

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About KoritheMan

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

Local Weather

Mostly Cloudy
53 °F
Mostly Cloudy