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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.

Hurricane Tomas enters the Caribbean Sea. . .

Posted by Sheena Parveen under Daily updates

Hurricane Tomas, now a category 2 hurricane, has already moved across the Lesser Antilles, and now it heads for the Central Caribbean Sea where water temperatures are very warm and atmospheric conditions are favorable for strengthening.   Water temperatures are currently in the mid 80’s in the Caribbean, and wind shear is low enough to allow Tomas to become a major hurricane soon.

Tomas will continue on a westward path until it interacts with a cold front by the end of the week.  This front will approach Tomas from the West, pushing it away from the U.S.  Many models expect Tomas to move NE at the time it interacts with the cold front.

Models expect this turn as Tomas interacts with the frontal boundary. 

The GFS model develops Tomas as a major hurricane by Thursday, then turns the storm to the NE over Hispaniola as the cold front approaches from the West.

So Long, Shary; Tomas Tears across St. Lucia

Posted by Andy Johnson under Daily updates

Hurricane Shary weakened to tropical storm strength Sunday afternoon and was also declared extra-tropical by the NHC. A cold to the west of Shary caught up with the storm and the combination of high shear, low water temperatures and the baroclinic frontal system caused Shary to become a post-tropical system.  Post-Tropical Storm Shary will continue to move rapidly ENE  across the northern Atlantic but the NHC has issued its last advisory on Shary.

Hurricane Tomas strengthened rapidly today and winds were sustained at 90MPH at 6PM on Sunday, October 30, 2010 as the system was passing just south of St. Lucia. St. Lucia is a popular vacation destination spot with beautiful resorts and, unfortunately, there have been Ham radio reports of widespread damage on the island. The eye of Tomas moved through the channel between St. Lucia and St. Vincent. There have been lots of damage reports from St.  Vincent, as well as, Barbados, which was the first island hit by Tomas. Tomas is a classic Cape-Verde type hurricane. It is very rare to see a storm of that type so far south and east this late in the year. In fact, Tomas is the first hurricane to pass through the Windward Islands (the part of the Lesser Antilles south of 16N this late in the year since 1724. Tomas is expected to intensify into a major Category 3 hurricane later this week south of Hispaniola. The long range forecast calls for an upper level trough to pick up Tomas and move him northward by later in the week. If the trough does not cause Tomas to recurve he could continue further westward into the Caribbean Sea.

The enhanced GOES satellite image below shows the circular central dense overcast of Tomas when the center was just southwest of St. Lucia. Hewanorra airport on St. Lucia was closed due to flooding. As early as Noon EDT on Sunday, St. Lucia reported wind gusts of 69 MPH. The airport stopped reporting after that and before the strongest winds hit St. Lucia. So, it appears that the worst weather in the northern eyewall passed directly over St. Lucia. Even further north at Martinique winds gusted to 45 MPH and winds in Dominica gusted to 40 MPH. There is also a large convective cluster east of the center of Tomas which will continue to bring heavy rains of 4″ to 8″ across the Windward Islands.

The structure of Shary (shown below) has become elongated northeast-southwest and no longer resembles a tropical structure. As a result, Shary is an extratropical storm now.

 The Martinque radar shown below at 5;30 PM EDT, Sunday, October 30, 2010 shows a clearly defined eye located southwest of St. Lucia. The heaviest curved spiral bands were passing right over the island of St. Lucia at that time.

The GFS model valid Monday at 8PM shown below indicates that Tomas will likely be located south of the Dominican Rebublic with a blocking ridge to the north.

The GFS model below shows that by Friday at 8:00 AM, could begin recurving to the north due to a weakness in the subtropical ridge caused by an East Coast trough.

Hurricane Shary speeds away while Hurricane Tomas organizes

Posted by Sheena Parveen under Daily updates

Hurricane Shary is quickly moving off into the cooler Atlantic waters at a speed of 35mph.  This system poses no threat to the U.S. and will dissipate soon.  It’s hard to see where the weak hurricane is, since it is getting caught up in a cold front.

The track keeps it moving NE along with the front, and soon it will dissipate as conditions deteriorate.

As for Tomas, it is now a category 1 hurricane.  It’s continuing to be organized with more thunderstorm activity near the center today, increasing the wind speeds to 75 mph.  Outflow bands from the storm are apparent, and that indicates low wind shear which will continue over the next several days, possibly strengthening this system to a major hurricane.  Parts of the Lesser Antilles are experiencing hurricane force winds now, along with heavy rain.

Tomas will continue West/NW into the Caribbean Sea, where it has the potential to grow into a very large and strong hurricane.

By the time Tomas near Jamaica, a cold front will exit the Southeast U.S.  This front will act as a wall, not allowing Tomas to move closer to the SE coast.  The storm at that time will either turn South or NE.  The computer models below agree on this cold front interaction, but they are not all agreeing on what direction Tomas will take once it encounters this front.

The GFS model turns Tomas into a major hurricane by next week in the Caribbean Sea, then turns it to the NE with the approach of the cold front.

Tropical Storm Shary and Tomas make 19 named storms for the season

Posted by Sheena Parveen under Daily updates

With the formation of Tropical Storm Shary and now Tropical Storm Tomas, we now have had 19 named storms for this Atlantic hurricane season.  There have now been 21 storms in total, 10 of which have been hurricanes, and 8 of which have only gotten to tropical storm strength.  This hurricane season is now tied with the 5th most active hurricane season ever on record.   On August 5, 2010, the National Hurricane Center issued an outlook of 14-20 named storms, 8-12 hurricanes, and of those hurricanes, 4-6 being major hurricanes. 

Tropical Storm Shary, which was Invest 92L earlier, is gaining organization in the Atlantic Ocean, but is not a threat to the U.S.   This storm does not have much thunderstorm activity associated with it due to the invasion of some dry air.  This storm is getting closer to hurricane strength as it moves N/NE near 12 mph.  Shary will soon be interacting with another cold front to the West of the storm, which will push it to the NE and eventually absorb or cause the system to dissipate.

The track is narrow because so many computer models are predicting the NE movement of Tropical Storm Shary as the cold front nears.  At this point, the storm has not other choice but to continue in this path.

Tropical Storm Tomas has now formed from Invest 91L.  Organization is very obvious as the tropical storm has maintained a cyclonic flow.  Large and well organized outer bands are apparent with this system, which is indicating low wind shear, conducive for further development.

In several days, this system will interact with a cold front moving off the Southeast U.S. coast, which should ultimately hold this storm to the South.  Some computer models already pick up on this at the end of the forecast period, as they take a sharp turn to the N/NE.  Either way, this storm should cause strong winds and heavy rain for islands in the Caribbean Sea.

The track of Tomas continues it W/NW into the warm waters of the Caribbean Sea, where water temperatures are will into the mid 80’s.  By next week, conditions could be favorable enough for Tomas to develop into a major hurricane.

By next Thursday, the GFS model expects Tomas to be a strong storm,  possibly a strong hurricane at this point.  But a cold front will also be exiting the U.S. at that time, nearing Tomas from the NW, holding it South of us.

As U.S. temperatures cool, tropical waters remain warm

Posted by Sheena Parveen under Daily updates

Many areas around the country are experiencing fall, with some parts of the U.S. experiencing blizzards from the strongest storm system to ever hit the Midwest.  An all-time record low pressure was reported of 28.20″ (954.9 mb) in Bigfork, Minnesota on October 26th.  Despite the cooler temperatures filtering into the U.S., tropical water temperatures are still on the warm side, conducive for tropical development.  Water temperatures are still in the mid 80’s in the Caribbean Sea, mid to low 80’s in the Gulf of Mexico, and near 80 degrees closer to Bermuda. 

A few tropical waves have formed and become better organized since 24 hours ago.  There is Invest 90L, Invest 91L, and Invest 92L.

Invest 90L is about 1200 miles NW of the Cape Verde Islands.  It is likely that gale force winds are occurring within this system; winds of 34 to 47 knots (39 to 54 mph).  There is a chance for this system to continue developing further.

No matter what the outcome of 90L, the system will be directed to the North as a cold front sweeps near and high pressure builds in to its West. 

Invest 91L is 1000 miles E/SE of the Windward Islands.  This system is currently very unorganized, but it does have the potential to slowly develop as it tracks to the W/NW.

Computer models move the storm through the Caribbean over the next several days, some models moving the storm farther North than others. 

Invest 92L is the most organized of them all so far.  An area of low pressure is forming in this system, and atmospheric conditions appear to be favorable over the next few days to form a subtropical or tropical depression.  92L is about 700 miles SE of Bermuda.

As with Invest 90L, a cold front will approach from the West and push this system North.  High pressure will also build in to the West of the cold front, keeping this system away from the U.S.

Eastern Atlantic Still Active

Posted by Andy Johnson under Daily updates

This year is already the 6th most active Atlantic hurricane season on record. Officially, hurricane season continues until November 30. In some rare cases, December hurricanes have been observed. It is very unlikely we would break the all-time record of 28 named storms  set in 2005 but we could end up being in the top 5 most active seaseons before 2010 is over.

Oddly enough, the eastern Atlantic continues to be fairly active this late into October. Usually, in late October and November our focus is on the western Atlantic, Gulf of Mexico and Caribbean Sea for tropical development.  Invest 90L is fairly far to the north in the eastern Atlantic and will be encountering cooler temperatures over the next few days. However, convection has become more circular in appearance today and the NHC gives the system a 30% chance of becoming a tropical cyclone in the next 48 hours. Steering currents are very weak so Invest 90L is nearly stationary. The light shear could allow some development.

Invest 91L developed today and is located further south than Invest 90L  Invest 91L is over warmer waters than 90L and shear is also low over 91L . Some of the longer range models have 90L becoming a tropical depression or storm by the first part of next week. One scenario has the system moving into northern South America and another scenario would be for the system to intensify more over the central Caribbean.

A third system northeast  of the Leeward Islands is associated with an upper level low interacting with a surface trough. Over the next few days, this system could build downward in the atmosphere and potentially become a subtropical depression or storm.

The satellite image below is a closer view of the trio in the Atlantic. The moisture field around Invest 91L has increased quite a bit today. Notice the stream of moisture connected all the way back to another tropical wave getting ready to exit Africa in the Sahel region.

The GFS model shown below is valid at Friday at 8:00 PM. There is a large high pressure area north of Invest 90L  which will block recurvature in the near term. The GFS strengthens the subtropical low more than Invest 90L north of Hispaniola by Friday night.

The longer range GFS model valid Tuesday morning is shown below. By then, it has Invest 90L recurving into the northern Atlantic and the subtropical low weakening. Invest 91L is shown as a possible depression north of Venezuela.