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Invest 94L brewing in the Caribbean Sea. . .

Posted by Sheena Parveen under Daily updates

No better organized than it was yesterday, Invest 94L is still brewing in the Southern Caribbean Sea.  Water temperatures in the Caribbean are still in the mid to low 80’s which is warm enough for tropical development.

Computer models aren’t doing anything too impressive with this system.  It should be held back from moving too far North as it encounters a cold front approaching from the NW by next week.

The GFS model picks up on this system, but by next week, once it encounters this cold front, it shows the system being pushed back to Central America, then dissipating. 

New Invest Area in the Caribbean

Posted by Andy Johnson under Daily updates

The remains of Tomas continue in the form of a remnant low just to the east of a cold front emanating out of a large extratropical low off of New England. One of the main feeder bands on the east side of Tomas as he was moving northward through the southeastern Bahamas became detached from the circulation of Tomas over the eastern Caribbean Sea. The NHC identified this area of heavy convection as Invest 93L on Tuesday, November 9, 2010. Wind shear is low in the Caribbean and water temperatures are still in the mid-80’s. There is no apparent circulation, however, and, as a result, the NHC is giving 93L only a 10% chance of developing into a tropical cyclone in the next 48 hours. The area of heavy rain should begin to move slowly northward and could bring some flooding rains to Puerto Rico and the Virgin Islands over the next few days.

Another tropical wave in the eastern Atlantic is producing a lot of thunderstorms but has no circulation and is undergoing shear.

A closer image of Invest 93L shown below indicates that the heaviest convection was located south of Puerto Rico and the Virgin Islands. However, if it moves northward heavy rains could overspread Puerto Rico and the Virgin Islands tonight and Wednesday.

 Most models shown below indicate that the system should head north and probably not directly affect Haiti, although the Dominican Republic could be affected. A few models are indicating more of a westward motion in the western Caribbean.

The GFS model valid at Thursday at 8:00 AM does not intensify Invest 93L to a depression. The model does show a large lumbering extratropical low in the western Atlantic which could bring large swells all along the eastern seaboard later in the week.

The GFS model valid Sunday at 8:00 PM still shows Invest 93L as a tropical wave, but the GFS model takes the system westward into the western Caribbean.

Tomás No Más

Posted by Andy Johnson under Daily updates

The National Hurricane Center issued its last public advisory on Tomas at 5PM Sunday, November 7, 2010. The combination of cold dry air with a cold front just to his west and very strong shear caused Tomas to rapidly weaken Sunday and become a post-tropical storm.

The circular center of Tomas can be seen in the image below but what is left of his convection remains in a small area to the north and east of the center of circulation.

The GFS model valid Tuesday at 8PM shows a large extratropical cyclone to the northwest of Tomas. The extratropical low will eventually absorb Tomas into its circulation.

Tomas was a hurricane earlier, now a tropical storm

Posted by Sheena Parveen under Daily updates

Tomas regained hurricane strength Saturday evening, but now the storm is back to tropical storm strength as atmospheric conditions deteriorate for it.  The storm is encountering a cold front now.

It will continue to the NE, then dissipate over cooler Atlantic waters.

Computer models are also taking it to the NE.

Tomas Regains Hurricane Strength

Posted by Andy Johnson under Daily updates

Seemingly, against all odds, Tomas strengthened Saturday evening as he moved northward towards colder water ahead of an approaching cold front. A NOAA Hurricane Hunter plane found that winds had increased to 75 MPH at 7:15 PM EDT, November 6, 2010 and Tomas was upgraded to hurricane strength for the third time in its history. Enhanced satellite pictures also have shown an increase in convection tonight along with a circular appearance to the convection. By 8:00 PM EDT, winds had increased even further to 80 MPH.

The GFS model valid Monday at 7:00 PM shown below shows a strengthening extratropical cyclone off of the New England coast. Several models indicate that the non-tropical will absorb Tomas into its circulation by  Wednesday. A few models continue to take Tomas eastward into the Atlantic. At any rate, Tomas should not have any more affect on the Caribbean Islands and will not affect the United States.

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Tropical Storm Tomas will continue to weaken

Posted by Sheena Parveen under Daily updates

Tomas, once a hurricane, blew past Haiti on Friday packing winds of 85mph with strong storms.  It has now decreased to a tropical storm and is moving over the Turks and Caicos, just North of Hispaniola.  It’s getting caught up in the cold front that moved through the Southeast, and this will keep the system away from the U.S., ultimately pushing it off into the Atlantic, then it will dissipate.

Tropical Storm Tomas may keep it’s current strength for the next 24 hours, but it will rapidly weaken as it becomes more absorbed into the cold front to its West.

Computer models also show this NE turn as the cold front interacts more with the storm.  Remember, hurricane season doesn’t end until November 30th.  Currently, there are no other significant tropical waves.

Tomas Strengthens Again; Threat to Haiti

Posted by Andy Johnson under Daily updates

Despite seemingly favorable atmospheric conditions today, Tomas continued to be weak most of the day after weakening to a tropical depression at 5 AM EDT, Wednesday, November 3, 2010. Tomas had succumbed to moderate southwesterly shear two day ago and never regained a vertical structure. Winter storms (baroclinic) tilt with height towards colder temperatures. Tropical systems need to remain vertically oriented  in order to intensify. Tropical system are barotropic and do not get their energy from temperature differences as winter baroclinic systems do. That is why hurricane are unique in possessing an eye. Satellites or aircraft can see right into the center of the structure which is vertically stacked. The southwesterly shear that Tomas was experiencing separated the heaviest convection from the circulation center.

Evidence from a hurricane reconnaissance aircraft this afternoon showed that the center of Tomas redeveloped to the northeast closer to the center of heaviest convection. As a result, the NHC upgraded Tomas back to tropical storm strength at 5PM Wednesday. Hurricane watches in Jamaica were changed to tropical storm watches since by the time Tomas begins to intensify, its circulation will be interrupted by the terrain of Jamaica and Hispaniola. However, since Haiti will likely be on the stronger east side of the storm a hurricane watch has been issued for Haiti.

The long range forecast still calls for an east coast trough to pick up Tomas and move him to the northeast. The trough weakens and flattens out by the weekend, however, leaving Tomas in a weak steering environment. As a result, Tomas could meander for days. If he is over open water at that time, it would not be as much of a problem. If Tomas stalls anywhere near Haiti, however, just the heavy rains (even without hurricane force winds) could could major problems with flooding. Haiti has been largely deforested while the adjacent Dominican Republic has not suffered the same fate.

The close-up enhanced satellite image below shows an elongated area of convection oriented northeast-southwest. High cirrus clouds around the periphery of the storm show a good outflow pattern and no significant shearing, both of which are indicators of strengthening.

Another tropical wave is located near Guyana on the north coast of Venezuela (shown below). Some models shows this system strengthening to a tropical depression or tropical storm next week.

Most of the models (shown below) have a general consensus of bringing Tomas northward somewhere between Jamaica and Haiti. The GFDL shows Tomas looping back to the south.

The GFS model valid Friday at 8:00 PM shows Tomas near the Turks and Caicos Islands after being picked up by the East Coast trough.

The longer range GFS valid Tuesday at 7:00 AM show  Tomas still around in the Atlantic and shows him being blocked by an East Coast ridge which will have replaced the trough at that point in time. The GFS also tries to develop a new depression or storm. The next name on the list is Virginie.

Tomas a Potential Threat to Haiti & Jamaica

Posted by Andy Johnson under Daily updates

The areal extent of heavy convection associated with Tropical Storm Tomas has continued to increase today as the overall environment surrounding the storm becomes more moist. The appearance of the convection is not circular or banded so there does not appear to be more organization taking place. A hurricane reconnaissance plane is investigating the storm Tuesday afternoon and as of 2:30 PM had not found a strengthening system yet. However, with less shear, a very moist environment and near record warm water temperatures, all indications are that Tomas will re-strengthen and will likely become a hurricane once more.

Haiti has the highest probability of a direct strike at this point in time, followed by Jamaica and the Dominican Republic. All of the the large scale models have been showing a deep trough moving eastward towards the U.S. East Coast and then continuing out to sea, which would turn Tomas to the northeast. In the longer time range period, the deep trough begins to lift out by this weekend. As a result, Tomas will be left in an area of weaker steering currents. In addition, by the weekend a ridge of high pressure in the upper atmosphere will begin building over the U.S. East Coast replacing the trough. The end result it that Tomas could slow down by the weekend and cause torrential rains wherever it slows down. This could occur west of Haiti or north of Haiti near the Turks and Caicos or even out at sea. The worst case scenario would be for Tomas to slow down in forward speed just to the west of Port-au-Prince, Haiti. Remember that there are still thousands of people displaced from the January earthquake which devastated the region. In addition, many of the mountains to the east of  Port-au-Prince have been deforested. As a result, even if hurricane force winds do not occur, the potential for mudslides and flooding is of great concern. If hurricane force winds occur where many people are living in tents and makeshift structures, there could be great loss of life.

The radar image below is from the Curacao radar taken Tuesday afternoon. The rain areas do not appear very organized on radar. There is a large separate area of rain each of the A,B, C Islands (Aruba, Bonaire and Curacao) that is not near the center of circulation. This pattern has existed with Tomas for several days with a separate area of convection that trails to the east of the storm. This phenomenon is likely due to the southwesterly shear which has existed for a few days causing some moisture to be displaced east of the center.

The enhanced satellite image belows shows a much larger overall cloud cover with Tomas but it does not have a classical circular or comma shaped appearance. The clouds in the western Gulf are part of the trough which is moving east and expected to turn Tomas towards the northeast. A tropical wave in the eastern Atlantic shows no signs of intensifying at the present time.

A close-up satellite view of Tomas (shown below) indicates a ragged appearance to the convection associated with the tropical storm.

Wave height in the eastern Caribbean have decreased to 7.5 feet as Tomas has moved farther away in the southern part of the Central Caribbean.

 Some of the models such as the BAMS and NOGAPS (shown below) forecast Tomas to greatly slow down in speed by the weekend which could produce a long period of heavy rain over Haiti.

The GFS model forecast valid at 8:00 PM Thursday shown below indicates an East Coast trough picking up Tomas and turning him to the northeast.

However, note that by Monday at 7:00 AM, the trough has lifted out leaving Tomas in its wake and a strong ridge over the East Coast has replaced the trough. That scenario could slow the forward speed of Tomas or turn him south or even west.

Tomas Weakens but Still A Threat

Posted by Andy Johnson under Daily updates

Thomas weakened to a tropical storm Sunday and continues as a tropical storm on Monday, November 1, 2010. The weakening can be attributed to 20 knots of southwesterly wind shear which tilted the storm to the northeast at upper levels and separated most of the convection to the northeast of the center of low level circulation.  This afternoon, I’ve noticed that the areal coverage has increased and also convection is reorganizing closer to the center. This may indicate that the weakening phase has stopped. The NHC does expect Tomas to regain hurricane strength once again later in the weak.

The future track of Tomas depends on where, when and even if the long wave trough along the eastern U.S. picks up the storm and recurves him to the northeast. There are now at least two models that do not show Tomas being picked up by the trough. The GFS model continues to show landfall in Haiti, which would be doubly tragic as they are still reeling from the earthquake earlier this year.

There is another tropical wave east of the Lesser Antilles which has shown a slight increase in convection today. There are only two more names on the hurricane list - Virginie and Walter. It is possible that we could reach the end of the list before 2010 is over.

The enhanced satellite image below shows an increase in convection since yesterday but the convection is still asymmetrical and displaced mostly east of the low level center of circulation. Some new convection has formed  far west of the center and could be entrained into the circulation as the wind shear gradually weakens over the next few days. Notice that the circulation is pretty far to the south and some convection is very close to Aruba, Bonaire and Curacao, as well as, Venezuela.

Tomas is kickup up seas to 13.1 feet in the eastern Caribbean.

 The wind shear forecast shown below indicates that wind shear will be light (blue areas) over Tomas in the next 48 hours. The stronger wind shear shown in yellow will remain further to the north.

Notice in the  plot below that two models, the NOGAPS (shown in green) and the GFDL (shown in red) stall Tomas in the Caribbean and do not complete recurvature into the Atlantic.

The GFS model shown below valid at 8:00 PM Wednesday, show a stronger Tomas south of Jamaica.

The GFS model shown below valid at 7:00 AM on Sunday, shows a recurving Tomas in the Atlantic north of Haiti. If the GFS forecast plays out, it could be devastating to Haiti as they are still trying to recover from the earthquake damage.