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Major Hurricane Earl affecting the Virgin Islands, Puerto Rico

Posted by Andy Johnson under Daily updates

Earl became a major Category 3 hurricane at 11:00 AM EDT Monday, August 30,2010. Nearly ideal conditions exist for further strengthening. There is almost no shear and water temperatures are close to record high values. Officially, the National Hurricane Center (NHC)  is forecasting Earl to become a Category 4 storm, but a Category 5 is not out of the question. The official NHC forecast has the center of Earl passing near the eastern seaboard of the U.S. between Wednesday and Friday. Any deviation in path to the west or east could  have great impacts along the coast. If the center stays far enough out to sea to the east, the impacts will be minimal. If the eye makes landfall along the east coast, the consequences are more dire. It is too early to say at this point, the exact path. Florida is not in the cone of danger but the area from North Carolina to Maine is in the cone of danger.

This morning the center of the eyewall has been passing just north of the the Leeward Islands. The northernmost Leeward Island is Anguilla and Earl passed  just to the north of Anguilla at 9 AM EDT. Saint Martin/St.Maarten is the next island just south of Anguilla made up of a French and a Dutch side. The Princess Juliana International Airport in the Dutch part of the island of Sint Maarten. The Dutch side of the island is on the south side which was further away from the center of Earl than the northern French side of the island. The population of the island is about 75,000. Winds gusts were recorded at 68 MPH at 8AM EDT at the Princess Juliana Airport more than an hour before the point of closest approach. It is possible that winds gusted to hurricane force in Anguilla since Anguilla was closer to the center of the eye. Winds may have gusted to hurricane force also on the French side of the island (Saint-Martin) since it was closer to Earl than the Dutch side.

At 1:57 PM EDT on Monday, the southern eyewall was passing near Anegada, which is the northernmost British Virgin Island. Unlike most of the other Leeward and Virgin Island, Anegada is a fairly flat atoll. The other islands have higher elevations since they are volcanic. The population of Anegada is only about 200 so the worst part of Earl is affecting the island with the least population in the region.

In the Skytower OMNI image below, the outer bands of Earl are reaching St. Croix, where winds have gusted to 39 MPH but the central core of hurricane force winds are in the eyewall around the circular center clearly visible in the radar image.

The enhance satellite image below shows magenta colored areas representing the strongest convection mostly wrapped in the northern semicircle. This means that the strongest winds are likely to the north of the islands. At 12:48 PM EDT Monday there was a large feeder band with very heavy convection (magenta) that was headed for the north coast of  Puerto Rico.

The St. Croix harbor cam picture we are carrying on our website is located in Christiansted located on the north central coast of St. Croix. St. Croix is protected by barrier reefs which cuts down on wave action somewhat. Tides are running above normal but there is not a lot of wave action in the protected harbor due to the reef. The camera is facing north.

The warning map as of 1PM EDT Monday is shown below. All warnings forAntigua, Barbuda, Montserrat, St. Kitts and Nevis were dropped and these islands did not have as much effect from Earl since they were further south. For Monday afternoon and evening the greatest threat will be to the northern U.S. and British Virgin Islands, Puerto, Culebra and Vieques, especially the northern facing coasts of these islands. A tropical storm warning and hurricane watch is in effect for Puerto Rico but may be upgraded to a warning later today. A hurricane warning is effect for Puerto Rican islands of Culebra and Vieques, which are the islands west of St. Thomas.

The Puerto Rican web camera image we are carrying on our web site shown below at about 2:00 PM EDT is in Luquillo, Puerto Rico. Luquillo is on the northeast coast. Large waves can be seen breaking on the beach there. Compare the Luquillo beach area to the protected harbor at Christiansted, St. Croix. 

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 The vortex message from the Air Force reconnaissance flight into Earl is shown below along with the entire flight path. At 11:27 AM EDT on Monday, they reported surface winds of 124.3 MPH with flight level winds of 133.5 MPH. The eye was circular but open in the southwest quadrant.

The McIDAS image shown below was taken at 8:0o AM EDT Monday shortly before the closest point of approach to Anguilla. The northern eyewall appears stronger in this image than the southern edge which was closer to Anguilla. Fortunately, then Anguilla did not receive the strongest part of the storm . The population of Anguilla is about 13,500.

The basin-wide satellite image below shows that Danielle has moved well into the mid-latitudes and does not have the same shape and structure of a tropical system such as Earl (shown near the center of the image). Danielle should become extratropical over the next 24 hours.

Invest 97L could still become a depression or tropical storm over the next few days. Invest 97L is moving west at 20 MPH. Earl is moving WNW at a slower speed of 15 MPH. Invest 97L is “gaining” on Earl and since Earl will be the stronger of the two systems, Earl will likely inhibit any rapid strengthening of Invest 97L especially as 97L gets closer to Earl. It is too early to say what there final interaction will be.  There is still yet another tropical wave with a potential to become a depression that is near the Cape Verde Island. It emerged off of Africa south of where Danielle, Earl and Invest 97L did.

Earl bears down on the Leeward Islands

Posted by Andy Johnson under Daily updates

Danielle is accelerating to the NNE on strong southeasterly upper level winds. The satellite image below shows the drier air being entrained into the southern part of the circulation and the center is devoid of deep convection. When Danielle stronger on Saturday there was a large anti-cyclone above the low level circulation of Danielle. The clockwise circulation of the upper high was causing northeasterly shear on Earl, which was located south of the upper high. Now that Danielle and its accompanying upper level high have moved away, it allowed Earl to strengthen without being inhibited by northeasterly shear.

Of all the tropical systems currently in the Atlantic, Earl has the potential to cause the most problems. The most immediated areas that are being affected are the Leeward Islands. There is the possibility that Earl could directly or indirectly affect the U.S. eastern seabord from Wednesday through Friday of the upcoming week.

Invest 97L located east of Earl has shown a decrease in convection today. None of the models intesify invest 97L anywhere nearly as strong as Earl is forecast to become. Earl is forecast to be a Category 4 hurricane east of the Bahamas. For the same reason that Danielle inhibited Earl, Earl may also inhibit the development of Invest 97L. As Earl strengthens a large upper level high will develop over Earl. The ouflow and subsidence will likely prevent Invest 97L from any rapid intensification.

There is yet another wave moving off of Africa which bears watching. The latest wave located east of Invest 97L is exiting Africa even farther south than Earl or Invest 97L did. Earl is destined to track further west than Danielle did. Without Earl, Invest 97L would likely also track further west. However, the interaction between a strong Earl and a weaker 97L in 3 to 5 days could cause a Fujiwhara affect (where two cyclones rotate around each other) or more likely recurve Invest 97L out to sea further east than Earl.

The tropical wave in the western continues to produce large areas of clouds and convection but without any circulation. The low in the northern Gulf appears to have moved inland over Louisiana and is weakening.

The enhanced satellite image of Earl shown below indicates the circular central core in magenta where the strongest winds are, as well as a strong feeder band to the east. There is also a strong line of convection which preceeds the hurricane which spread over most of the Leeward Islands Sunday afternoon.

Even though Danielle, passed almost 300 miles east of Bermuda and much further away from Florida, large swells that were formed when Danielle was a Category 4 hurricane are impinging on the east coast of Florida causing dangerous rip currents. Seas of 8.5′ were reported at the buoy near Cape Canaveral on Sunday afternoon. Here in the Bay area we do not have to worry about rip currents since the swells will break on the east coast and our flow will continue to be east to northeast (offshore flow).

the graphic below shows wave height in the western Atlantic. They increase closer to the center of Danielle. Just about time the waves will start to settle down from Danielle, Hurricane Earl will produce more swell from the southeast. Thus, much of the east coast of the U.S. from Florida to Maine will experience large waves and dangerous rip currents this week.

The Martinique radar from METEO France shown below clearly identifies the eye of Earl located east of the Leeward Islands on Sunday evening. The improving structure can be seen between 23 UTC 8/28/10 (second image below) and 0215 UTC 8/29/10 (first image below). Notice the eye getting more circular and defined.

The warning map below shows the status of warnings as of 11PM Sunday night. Since Anguilla, St. Martin and St. Barthelemy are located the furthest northeast in the Leeward Islands they will experience the brunt of Earl first.

A NOAA P3 aircraft found flight level winds of 77 MPH on Sunday afternoon at 6:03 PM. However, Earl has continued to rapidly intensify since the image. The graphic below shows the flight path of the aircraft.

The storm surge is expected to be 2 to 4 feet above ground level near the coast in areas of onshore winds in the Leeward Island. The smaller islands are not as susceptible to high storm surge as are large coastlines with shallow continental shelves. I had the opportunity to visit St. Barthélemy earlier this year. I am standing in the capital city of Gustavia, St. Barthémely in the picture below.  Notice that many homes are built close to to sea level in the protected harbor city, which is is on the south side of the island. If Earl passes to the north of St. Bart’s, Gustavia should fare well regarding storm surge. Many of the the Leeward Islands are volcanic, so many homes are also able to built high on the hillsides above any potential storm surge.  

In the picture below, the downtown shops are on the right. Notice that the main street is only about 4 feet or so above sea level.

The map below shows the protected port area of Gustavia.

The picture I took below was from a ship off the coast looking northeast towards Gustavia. The downtown area is where the red roofed building are located.

As of 11PM, the British Virgin Islands were under a hurricane warning and the U.S. Virgin Islands such as St. Thomas shown below were under a hurricane watch. The warning may be extended westward on Monday. I took the picture below from a hillside above the capital city of Charlotte Amalie looking south-southwest towards the harbor and downtown area. Charlotte Amalie is also on the more protected south shore of St. Thomas, U.S. Virgin Islands.

In addition, as can be seen in the picture I took below looking southwest other islands are evident which serve to break up wave action.

Danielle weakens, Earl strengthens, “Fiona” on the way?

Posted by Sheena Parveen under Daily updates

‘Tis the season for an active tropical set-up. . .

We are still watching Hurricane Danielle, Hurricane Earl, and Invest 97L, all located in the Atlantic.

Hurricane Danielle will continue to stay away from the United States as it moves on a N/NE path.  Cooler waters and higher wind shear ahead will destroy this system over the next several days.

As of the 11am advisory from the National Hurricane Center, Earl has been upgraded to a category 1 hurricane.  It’s gained organization and wind speed over the past 24 hours.  Through the end of next week, atmospheric conditions are looking favorable for strengthening of Earl.  At that time, it may be a major hurricane (category 3+).  The good news right now for the Southeast is an area high pressure in the forecast at the time Earl will be closest.  This will help block it from the Southeast U.S., and another area of high pressure in the Atlantic will help steer it to the North.  Hopefully this will follow closely to Danielle’s path, but a forecast this far out can always change.

As for Invest 97L, a tropical depression is not far in the future. . .  We could see one form in the next 24 to 48 hours.  As of  now, computer models are agreeing on another path, similar to Danielle’s, several days from now.

Wind shear ahead of Earl and Invest 97L is fairly light.  Conditions as of now look more favorable for Earl to develop into a strong storm system, whereas Invest 97L may run into some moderate shear at times.

The HWRF model suggests Earl becoming a major hurricane, skimming the East coast, with Invest 97L following behind, weaker.  This is an extended computer model forecast for September 3rd, which we cannot rely heavily on at this time, but it does seem somewhat likely.

Tropical Trio on the way?

Posted by Andy Johnson under Daily updates

As expected, we have entered a very active period in the tropical Atlantic. Hurricane Danielle has become a large hurricane and is currently the strongest feature. There is good news for Bermuda.,however. All tropical storm watches and warnings were cancelled for the island Sunday afternoon. The main problem will be large swells generated first by Danielle and later by Earl which will cause an extended period of huge wave all over the western Atlantic Ocean. Big waves will affect most of the east coast of the U.S. over the next week with the likelihood of rip currents. Danielle will recurve and become a huge extratropical storm over the north Atlantic in the next 3 to 5 days.

The main concern will now be Earl. Earl could be a dangerous category 3 hurricane off of the eastern seaboard during the upcoming week. Danielle is moving through a weakness in the Bermuda-Azores high. Ironically, as Danielle becomes a monster extratropical storm in the far north Atlantic, she will indirectly cause relative pressures to rise off the east coast of the U.S. This effect will allow Earl to come much farther west than Danielle did and could allow Earl to threaten the east coat of the  U.S. by mid-week. In addition, eventually the remains of Danielle will move back to the west south of Greenland which could induce a blocking pattern north of Earl mid-week. This may allow Earl to sit for a long time off of the east coast. Usually storms accelerate northward off of the middle Atlantic but this may not be the case with Earl.

In addition, another system (Invest 97L) will likely become a depression and possible Tropical Storm Fiona over the next days. Due to the rapid movement of Invest 97L and the outflow from Earl as he strengthens, Invest 97L will not likely achieve the same strength as Earl will achieve. There is the possibility of a Fujiwhara effect where two storms rotate around each other or Earl could eventually absorb 97 L (future Fiona?).

Another strong tropical wave just coming off of Africa is also a candidate for becoming a tropical cyclone this week The distubance in the Caribbean remains unorganized. The low in the Gulf is non-tropical and will be moving northward onshore by Sunday and Monday.

The enhanced satellite view below shows that although Danielle is the largest current system, cloud tops are cooling. The coldest cloud tops (magenta colors) are now associated with Earl as he strengthens in purely tropical waters.

Wave height are already picking up. Waves near Danielle are more than 25′ high. The buoy west of Bermuda is reported 9.2′ swells on Sunday afternoon.

The Bermuda radar shown below indicates that the outer bands of rain with Danielle are affecting Bermuda as they rotate from the north-northeast to the south-southwest.

The long range GFS model below is valid for Friday at 9:00 AM. Remember that there are large errors this far in advance. However, the general trend is that the remains of Danielle will be a mega-storm in the north Atlantic, Earl will be very strong off or near the east coast of the U.S. and Fiona? may be overshadowed by Earl.

Danielle weakens, Earl expected to strengthen

Posted by Sheena Parveen under Daily updates

There are 3 systems in the Atlantic to keep an eye on.  First, Hurricane Danielle, which has been downgraded to a category 2.  Second, Tropical Storm Earl which isn’t visibly showing any better signs of organization, but wind speeds have increased, indicating strengthening.  Third, we have a tropical wave, Invest 97L, which may become our next named storm.

Hurricane Danielle has weakened to a category 2 hurricane, and continued weakening is expected as it moves into higher wind shear and cooler waters.  An old frontal boundary moving off the Northeast will push Danielle back out to sea, keeping it away from the United States.

Tropical Storm Earl will continue behind Danielle, possibly traveling in a similar path.  This storm is expected to near Puerto Rico as a hurricane, then head up the Atlantic.  A large ridge of high pressure over much of the Eastern seaboard should keep Earl in the Atlantic for most of the time, but it’s still too far out to be certain.

Invest 97L may be on a similar path as Earl, since computer  models are currently agreeing on a Northwest turn once near the United States.  This system may become a tropical depression soon, then possibly the next named storm which would be “Fiona”.

Through the extended period, the GFS doesn’t significantly develop Invest 97L, but it does keep Earl at a strong hurricane.  This is also something we’ll have to keep an eye on as the forecast becomes more uncertain with time.

There are pockets of light wind shear throughout the Atlantic where conditions are favorable for further strengthening of both Earl and Invest 97L.  As for Danielle, weakening will occur on a continued path to the NE.

Danielle becomes a major Hurricane

Posted by Jim Weber under Daily updates

The tropics have become quite active over the past week. Leading the pack is Hurricane Danielle which became our first major hurricane of the season overnight and has quickly become a category 4 hurricane with winds of 135mph this morning.

Satellite imagery shows a well formed eye with good outflow on nearly all sides of the storm. Computer models remain in good agreement moving this hurricane to the east of Bermuda over the weekend. Large swells will move thru the western Atlantic and even reaching the east coast of the US over the weekend.

Further out into the Atlantic is Tropical Storm Earl and Invest 97L which continues to show more organization this morning.

Models continue to show a more southerly track for Earl with an eventual turn towards the northwest. This track could put Earl very close to the Leeward Islands early next week.

Tropical Twins

Posted by Andy Johnson under Daily updates

The tropics continue to evolve into the active phase we have been expecting. Hurricane Danielle, which had briefly dropped back to tropical storm strength on Tuesday, has been solidly exhibiting hurricane characteristics Wednesday.  Conditions are generally favorable for slow intensification over the next few days. The central core of intense convection has increased in aerial coverage since yesterday. Banding has been most prominent on the east side of the hurricane which is consistent with the fact that Danielle has been experience some southwesterly shear.  Danielle has also broken away from the grip of the large Saharan Air Layer (SAL) which was partly responsible for her decrease in intensity on Tuesday. Most guidance continues to show recurvature. There is no threat for Florida. In the long term there is some uncertainty about whether the recurvature will complete before coming close to the Canadian Maritimes or possibly offshore of the northeast U.S. Residents of Bermuda should also monitor the progress of Danielle and Earl, as well. Tropical Depression #7  continued to show intensification with good outflow in the eastern semi-circle became Tropical Storm Earl at 5PM Wednesday. The enhanced satellite image below shows the high bright white cirrus clouds spiraling clockwise on the north and east sides of the system.

A new convective cluster is just now moving off of Africa. As it has been exiting the continent today, the areal extent of heavy convection has decreased leaving an unorganized, unsymettrical area of clouds and showers. Nontheless, there is a chance that this wave will slowly develop into a depression or tropical storm in the 3 to 5 day time frame. Note that each successive disturbance is exiting Africa at a further south latitude. The further south a wave exits Africa ,the more likely that is has a chance of making all the was across the Atlantic without being picked up and recurved by a mid-latitude trough.

The frontal wave in the Central Gulf of Mexico continues to produce a large area of unorganized but widespread convection in the Gulf. Steering currents will push this system slowly westward or southwestward away from Florida over the next few days. There is only a slight chance of this system developing into a depression before reaching the Texas coast. 

Convection persists in the southwestern Caribbean but there is no circulation evident.

The close-up enhanced GOES IR image below centered over Danielle shows a moderate sized area of deep convection. Two major feeder bands are located on the east side of the hurricane away from the influence of southwesterly shear.

The MODIS AQUA polar obiting satellite image below shows the large round central dense overcast (CDO) is just slightly off center to the right from the low level circulation which can be seen in the lower level clouds. This is another reason that only slow intensification is forecast in the near term.

The AQUA MODIS picture below is Earl. It does not have the circular appearance like Danielle (above) since it is an immature system at this point in time. There are still lots of heavy convective clusters, though.

The Saharan Air Layer (SAL) graphic below shows that Danielle has freed herself from the SAL dusty grip. Earl, however, is headed into a dry dusty area to the west. Eventually the new wave moving off of Africa,which will likely become T.D. #8, may encounter some dusty air in about 2 days. The dusty air inhibits tropical cyclone development and intensification.

Another technique to view the amount of moisture in the air is the water vapor satellite imagery. There is still a persistant layer of dry air west of Danielle with another slot west of Earl.  The moist circulation of Danielle seems to be eroding the dry patch of air further west, though.

As alway, use caution in looking at long range models since there is a great degree of uncertainty and wide errors. General trends can sometimes be gleaned from then, though.  The 12Z run of the GFS model show that by next Tuesday, Danielle will likely still be a hurricane and will be located east of New England. Earl will be located north of the Leeward Islands by that time. The new wave just moving off of Africa today, could become Fiona located east of the Leeward Island. Note that with each succesive storm, the track is a bit more south and west.  

Hurricane Frank fortunately missed a directly hit on the Mexican Riviera but could eventually bring some moisture to Baja California by Monday or Tuesday next week.

Danielle fluctuates/New Depression Forming

Posted by Andy Johnson under Daily updates

Danielle underwent a rapid strengthening phase overnight Monday and became a Category 2 hurricane on the Saffir-Simpson Hurricane Wind Scale at 5AM Tuesday morning. During the day, however, a weakening trend occurred and winds  decreased back to tropical storm strength at 5pm. At 11pM Tuesday, Danielle was back to huricane strength. As I mentioned in my blog yesterday, Danielle had been insulated from the large dry air mass situated to the west of the circulation. For a while the two areas were moving in tandem but today Danielle caught up with the drier air mass and I believe that is the primary reason she has weakened as drier air has been entrained into the circulation. There are several signs of evidence for the dry air intrusion. Water vapor imagery has continued to show an uncharacteristically large area of dry air (at least for the tropics in August) to the west of Danielle. In addition, the TRMM (Tropical Rainfall Measuring Mission) Satellite has shown a closed eyewall on the east side of Danielle but a partially open eyewall on the west side of Danielle. The TRMM satellite is a polar orbiting satellite that allows us to see rainfall rates. This satellite is especially useful in tropical ocean regions where there are no radars available. Due to the curvature of the earth, radar ranges are limited but satellites are able to view a much larger area. The erosion of the western eyewall is evidence of some drier air. The secondary reason for weakening is due to increased southwesterly shear. Southwesterly winds of 20 knots at the northern edge of the surface circulation of Danielle have begun today and some shear as high as 30 kts is located in the northern outflow region of the hurricane.

In the satellite image below notice that most of the high cirrus outflow is on the east side of Danielle, which is consistent with southwesterly winds aloft. Invest 96L: is close to becoming a tropical depression and is unusually that is was so strong even when it was over land in Africa. There are signs of a weak circulation and it is bringing gusty winds to the Cape Verde Islands. Usually, storms intensify west of the Cape Verde Islands so the Islands themselves do not get gusty winds. The station closest to the circulation center is Praia, Cape Verde.  At 11:00 AM today (local time) they reported a NE wind gusting to 24 MPH. At 5:00 PM (local time) they reported a SE wind at 14 MPH. The veering wind indicates that the center passed south of Praia and is now located to the southwest. It is interesting to note that observer at Praia, Cape Verde recorded widespread dust at 11:00 AM (only partly cloudy at 5:00 after the passage) and Mindelo, Cape Verde has reported widespread dust all day with winds out of the NE gusting to 27 MPH. Mindelo is further northwest of Praia. Another strong convective cluster is getting ready to move off of the African coast and may put even more of a damper on the extensive dust that has been blowing off of the continent.

A small low in the NW Gulf is causing above normal tides along the west coast of Central Florida due to a long fetch of southwesterly flow. Tides were running 2 to 4 feet above normal around Cedar Key Tuesday afternoon.

An concentrated area of convection persists in the southwest Caribbean Sea but without signs of organization or a surface circulation.

The image below is an enhance dview of Danielle taken by the GOES weather satellite. Compare this image with the images from my blogs over the past few days. Notice the magenta area which contains the coldest cloud top areas. The magenta area has shrunk since yesterday. Note that even the red areas are mostly to the east of the circulation center which is consistent with southwesterly shear.

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 The Saharan Air Layer (SAL) McIDAS image below shows the location of Danielle (to the west), Invest 96L in the middle and a new convective cluster over Africa (to the right).  The rightmost cluster could develop once it emerges off of Africa, as well. Even though the SAL is extensive, if you compare it to a few days ago or a week ago, there is less dust, at least at lower latitudes (from 10° to 20° N). Most of the African waves that develop into hurricanes emerge from 10° to 20° N.  As we say today from the report from Praia, Cape Verde, the dust diminished once the tropical wave passed to the west.

The image below shows upper level winds overlaid on a satellite image. The arrows shows the direction of wind and the circular yellow lines show the speed. Wind shear over the northern part of Danielle is between 20 and 30 knots and she is headed more into that unfavorable area for development.

The TRMM satellite image below shows the erosion of the western eyewall as the rain pattern is not concentric around the eye. There is a solid area of convection on the east side of the eye but not on the west.

Long range models are taken with a grain of salt but can show general trends. The long range GFS model below shows Danielle recurving but the next system (Earl?) possibly making it further west than Danielle is expected to move by next Monday.  

Tropical Storm Frank has remained offshore of the Mexican coast. The forecast cone shown below is now totally offshore. As a result, tropical storm warnings were dropped for Acapulco. Hopefully, cruises going to the Mexican Riviera can be re-routed effectively around this storm.

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Danielle strengthens to hurricane/New invest 96L

Posted by Andy Johnson under Daily updates

Tropical Storm Danielle continued to strengthen in the far eastern Atlantic and became a hurricane at 5PM Monday. The circulation center has stayed far enough away from the large Saharan Air Layer (SAL) in the eastern Atlantic to prevent dry air intrusion. Also, the SAL is not as strong or extensive as it was a week ago. There is still some east-northeasterly shear over Danielle but it is expected to weaken over the next few days, which will, in turn, allow Danielle to strengthen. An upper level trough of low pressure is expected to move eastward from the U.S. East Coast which will aid in breaking down the mid-Atlantic ridge and, thus, allow Danielle to recurve to the north in the 4 to 5 day time frame.  The current large scale pattern is much different than in the summer of 2004 and 2005 when the Bermuda high was much stronger and did not allow as many storms to recurve. Instead, many of the hurricanes in 2004 and 2005 were forced westward by the stronger ridge.

The convective cluster that was about to emerge off of the African coast that I noted in my blog yesterday has now been identified by NHC as Invest 96 L and has begun running forecast models on the system. It appears that the weakness in the subtropical ridge left by Danielle will also allow Invest 96L to eventually recurve to the north, also.

A weak low pressure area continues in the northeastern Gulf of Mexico and is expected to drift slowly northward. The origins of this low can be traced all the way back to the remnants of Tropical Depression #5. 

There has been a flare-up of convection in the southwestern Caribbean but there is no evidence of circulation as of Monday afternoon. Tropical Storm Frank continues to strengthen in the Eastern North Pacific and is paralleling the Mexican coast. Frank threatens to bring heavy rain to coastal communities including Acapulco.

The close-up enhanced satellite image of Danielle shown below shows a slightly more symmetrical pattern than yesterday when Danielle was oriented more northeast-southwest. The bright white clouds are high cirrus clouds and are confirming that an outflow pattern is developing above Danielle. In order to strengthen without filling, tropical cyclone must not only circulate moist warm tropical air at the surface but must also have a mechanism in the upper atmosphere to expel the descending air away from the core circulation. It appears that Danielle is doing this. Even though the circulation is more symmetrical than yesterday, the coldest cloud tops (shown in magenta) are not as extensive in areal coverage.

The GOES 13 image belos is a visible image showing the low level counterclockwise inflow of cumulus clouds and the high level cirrus clockwise outflow .

The water vapor satellite image below shows that there is still a large area of dry air in the path of Danielle. However, the drier air seems to be moving in tandem with Danielle.

 The long range GFS model forecast for Saturday at 8:00 PM (subject to large areas that far in advance)  shows Danielle trying to recurve in a weakness in the Azores-Bermuda high. The only concern for the U.S. or Canada would be if the high pressure area over New England at that time spread farther east into the Atlantic and blocked Danielle’s recurvature. It is too early to say if that would happen.

The latest guidance regarding Tropical Storm Frank off the southern coast of Mexico shows that it will parallel the coast without coming ashore. Nevertheless, Frank could affect popular cruise routes to the Mexican Riviera and bring heavy rains and gusty winds to the coastal states including the city of Acapulco.

Danielle develops

Posted by Andy Johnson under Daily updates

Tropical Depression #6 was upgraded to Tropical Danielle at 5PM EDT, Sunday, August 22, 2010. The enhanced IR satellite image below shows an impressive amount of convection for an incipient tropical cyclone. The large magenta area shows extremely cold cloud tops which are as cold as -85° C. The colder the cloud tops the more intense the convection. The shape of Danielle is still not purely symmetrical and is oriented more northeast-southwest. This is partly due to the influence of the tropical wave to the west of Danielle and easterly shear. Earlier today the easterly shear had caused the low level center to be exposed. Later in the afternoon, the center was located more directly under the intense convection. Due to the circulation center trying to relocate closer the heavy convection, the motion appeared to be more northwesterly. Now that the reorganization process has completed, a more west-northwesterly motion is forecast.

The basin-wide satellite image below shows the strong tropical wave located southwest of Danielle. It appears to have two centers of convection, one to the west of the Cape Verde Islands and one to the east of the Cape Verde Islands. Another tropical wave is located in the southwestern Caribbean causing heavy convection over Nicaragua and Honduras. Due to its proximity to land no short term intensification is forecast. Moisture that can be traced back to the remnants of Tropical Depression #5 is located in the northeast Gulf of Mexico. This is the third time, this system has been in the Gulf after looping through the southeastern states.

 The water vapor image below shows that there is still a lot of dry air in the eastern and central Atlantic. This will have some limiting influence on Danielle in a few days, although Danielle now appears to be far enough away so that there is not much dry air intrusion.

The GFS  model show a weakness in the Azores Bermuda high by this Saturday which would allow Danielle to recurve to the north.  There are some indications in the longer term that the ridge might build back a bit afterwards though prevented a rapid re-curvature. It is just too early to say at this point, when and where Danielle will recurve.

The NOGAPS model shown below does not show as much of a weakness in the mid-Atlantic ridge and takes Danielle much further south and west than the other models.  

Tropical Storm Frank has formed in the Eastern North Pacific and is expected to become a hurricane over the next few days. Since the forecast track is not too far offshore of Mexico, tropical storm warnings have been issued along the southern Mexican coast as far west as Acapulco. The outer bands could affect cruises headed for the Mexican Riviera over the next few days.