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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.

Tropical Depression #6 close to tropical storm strength

Posted by Sheena Parveen under Daily updates

Tropical Depression #6 has regained better organization from earlier Sunday morning.  As of 9am, it was close to tropical storm strength.  The next name on the list is Danielle.

Conditions appear favorable for further development as this depression moves across the Atlantic.  Our GFS model suggests this storm becoming a hurricane next week with a weaker storm following it.

The forecast path of this storm keeps it in the Atlantic.  High pressure in the Northern Atlantic Ocean will help steer the storm in this direction.  Intensity forecasts should not be heavily relied upon, but as of now, the National Hurricane Center says this storm may develop into a hurricane, possibly category 2, by the end of the work week.

Computer models are in tight agreement that T.D. #6 will take a sharp turn to the North by next weekend.  This will keep the storm in the Atlantic, away from the U.S.

Wind shear over T.D. #6 is fairly light, and is expected to remain light throughout the next week.  This will allow the system to further develop as it moves West/Northwest across the very warm waters of the Atlantic.

There is another tropical wave behind (to the East) of T.D. #6 which may have potential for development into a tropical system in the next several days.  Through the rest of the tropics, conditions are quiet with higher wind shear through the Caribbean and high pressure located in the Gulf of Mexico. 

Tropical Depression #6 develops

Posted by Andy Johnson under Daily updates

As expected, the tropical wave in the far eastern Atlantic about 400 miles southwest of the Cape Verde Islands intensified into Tropical Depression #6 today. The depression is elongated somewhat from the northeast to the southwest but convection has increased today. In addition, the low level circulation has become more defined with a southwesterly wind rotating into the system. All models are in consensus that the depression will develop into Hurricane Danielle over the next few days. Fortunately, for the United States and the Caribbean Islands, it appears the the system will re-curve in the next five to seven days in the Central Atlantic due to a weakness which will develop in the Azores-Bermuda high. It looks like there is a slight threat to Bermuda but most guidance suggests a path even further east than Bermuda.

The enhanced infra-red satellite image below shows some other features, as well. The moisture that was originally associated with T.D. #5 moved into Louisisana, then moved back over the Gulf and then again over Lousiana and is now causing above normal clouds and rain in Florida and the northern Gulf coast. There are no signs of re-intensification.

A tropical wave in the southwest Atlantic is getting close to moving ashore in Nicaragua and Honduras. As  a result, it does not have much of a time window to develop into a depression. Another huge convective cluster is over western Africa and is getting ready to emerge in the Atlantic by tomorrow. Models are not showing quick intensification with this system, but since it is so large I would not be surprised to see and invest area or depression form over the next few days. T.D. #9E in the Eastern North Pacific is expected to intensify and could brush some of the resorts on the Mexican Riviera such as Acapulco.

 There is still a lot of dry air in the eastern Atlantic as evidenced by the water vapor image below. T.D. #6 will be moving closer to some of this drier air, which is not conducive for rapid development, at least not in the near term.

The GFS forecast for Friday at 8:00 AM EDT is shown below. The GFS shows that Danielle will begin recurving at that time due to a weakness in the Azores-Bermuda high. Before Friday the mid-Atlantic ridge is stronger and would keep future Danielle from recurving. The GFS model is also picking up another system southeast of Danielle, which is likely the current wave getting ready to emerge off of the African coast. It also shows low pressure in the southwestern Caribbean.

The METEOSAT image below shows a more direct view of the convective cluster east of Dakar and another north of Lagos.  The circulation around T.D. #6 is also clearly defined.

 T.D. #9E will likely become a hurricane over the next few days. The outer bands could pose a threat to parts of the Mexican Riviera including Acapulco.

Watching Invest 95L. . .

Posted by Sheena Parveen under Daily updates

The tropical wave located near Africa in the Atlantic Ocean continues to hold the potential for further development, as atmospheric conditions will become more favorable for it over the next few days.  Currently, images of Invest 95L show a fairly unorganized system, no better than yesterday. 

By next week, many computer models are suggesting it becoming a much more organized system in the Atlantic.

High pressure in the Northern/Central Atlantic will help to steer this system North over the next several days.  This will turn it away from the U.S.

Wind shear is fairly low over the system, but is forecast to become more favorable over the next several days.

Elsewhere, there is one tropical wave moving in over Mexico, which poses no threat of development.  Other than that, the tropics are quiet.

Invest 95L expected to organize

Posted by Sheena Parveen under Daily updates

An area of low pressure in the tropical Atlantic Ocean, Invest 95L, has become better organized since early Friday morning.  As of the 8am advisory, it was 275 miles S/SW of the Cape Verde Islands.

Computer models have been picking up on this system since early this week, and they continue to forecast it strengthening and becoming more organized by next week.

This system will continue to move W/NW over the next few days, then take a sharp turn to the N/NW.  There is a good agreement in computer models on this track.

Conditions are expected to become more favorable for Invest 95L into next week, when we may see rapid strengthening.  The great news is it be mainly an “Atlantic” storm, staying away from the United States.

Tropical Development Possible In Eastern Atlantic

Posted by Dave Osterberg under Daily updates

While the rest of the tropics remain quiet, the Eastern Atlantic is showing signs of development. We are now in the prime time for storms to form, with the peak of the hurricane season being around September 10th. A couple of days ago a vigorous wave came off the coast of Africa, and although signs of development are slow, the Hurricane Center is giving this area a 20% chance of development in the next 48 hours.  You can see the disorganization on satellite, but the computer models are insistent that it will develop. Slowly this weekend we expect a tropical system to form, but keep in mind this is thousands of miles away, and to pinpoint where or how strong this system may get is impossible.

The one positive is that most of the computer models believe there will be a weakness in the big high pressure system over the Atlantic. That would allow this system to turn more toward the NW in the long term. But of course all that depends on timing, and the strength of the system. Here are some of the long term computer models, which you can see differ in intensity, but all seem to agree of more of a northwest turn. Stay tuned…

Heavy rains from remains of T.D.#5/Strong African wave

Posted by Andy Johnson under Daily updates

As expected, the greatest hazard with the remains of Tropical Depression #5 has been heavy rains, not strong winds. The slow movement of the remnant low has caused over 12″ of rain in central Louisiana just in a 24-hour period. As I mentioned in my blog yesterday, most of the strong convection had been pushed south of the circulation due to upper level winds out of the northeast. The northeast upper wind were caused by the clockwise circulation around a strong high pressure system that has been causing the heat wave conditions in the Southeast and the Southern Plains. A weakness  has developed in the ridge with two centers - one over Texas and one over Florida. The weak steering currents have led to the slow movement of the remains of T.D. #5 and, thus, the heavy rains. In tropical systems, the amount of rainfall is usually associated with the speed and diameter of the system, not the strength. So, a tropical depression moving at 5 MPH can cause just as much rain as a hurricane moving at 5 MPH. After the remnants of T.D. 5 moved inland, it allowed for the large convection over the coast to become parked over central Louisiana. As shown in the Skytower OMNI radar image below, most of the torrential rains missed the more densely populated areas like New Orleans and Baton Rouge and were concentrated east of Alexandria.

The basin-wide enhanced satellite image shown below shows that in addition to the remnants of Tropical Depression #5, there are several tropical waves that we are following. The wave in the Caribbean still shows a lot of convection approaching Jamaica. Southwesterly shear has been the main factor inhibiting this wave from developing. Shear will be less when it reaches the western Caribbean but by then it will be too close to the land mass of Central America for much development to take place. A tropical wave in the eastern Atlantic mainly south of latitude 10° N is moving along the periphery of the larger than normal dry Saharan Air Layer (SAL) covering much of the eastern Atlantic. Since this wave is so far south, the Coriolis force is not very strong and it has little chance of developing a rotational center. The Coriolis force is zero at the equator.  A much stronger tropical wave is moving off of the coast of Africa at a latitude that is further north than the initial wave. The continued movement of more of these waves off of Africa is moistening the dry environment that has existed throughout much of July and August in this region, leading to more instability.

The image above was taken from the GOES East satellite. The image below is from the European Space Agency’s (ESA) METEOSAT satelite.  The METEOSAT image confirms that several areas of convection are developing over equatorial African and are moving westward. Each of these convective clusters will likely eventually emerge off the African coast as tropical waves. Several of the long range computer models are indicated at least one and maybe two tropical cyclones developing from  these waves by the end of August. 

T.D. #5 Final landfall/Active phase coming

Posted by Andy Johnson under Daily updates

The remains of Tropical Depression #5 made its final landfall over Louisiana this morning. The main threat is heavy rain. As a result, the National Weather Service in New Orleans has issued a flash flood watch for much of southeastern Louisiana. Total rainfall of 3 to 5 inches is expected with localized amounts up to 8 inches is possible. The streamline analysis shown below is still showing a circulation over southern Louisiana. The wind are spiralling into the center as the system continues to fill and weaken.

The pressure field in the image below shows that barometric pressure is not very low. New Orleans was reporting a pressure of 1011.9 MB or 29.87″ at  2PM EDT, August 17, 2010.

The main problem will be heavy rains will likely cause flash flooding. Since most of the heaviest convection has been on the south side of the circulation center, up until now the heaviest rainfall has been over the Gulf. As the low moves northwestward and northward today, the heavy area of convection shown in the radar image below which is just south of the central coastal Louisiana parishes will overspread much of the southern half of the state.

Buoy 42040 southeast of the mouth of the Mississippi River reported just 3.6′ wave heights and wind of 20-22 MPH out of the south on the east side of the circulation center.

The basin-wide image shown below shows a flare-up of the eastern Caribbean tropical wave. The total amount and areal coverage of convection has increased a lot since yesterday. Two additional tropical waves are moving off of Africa.

Climatologically, we are not entering the most active period of hurricane development, especially of Cape-Verde type hurricanes. There are signs worldwide that the quiet pattern we have been under for much of this hurricane season is coming to an end. We have seen fewer named tropical cyclones so far this year in the northern hemisphere since reliable records began in the 1940’s. Large scale blocking patterns which caused the unprecendented Russian heat wave and flooding in Pakistan are now breaking down. Record heat is coming to an end in Moscow and the rains have stopped at least temporarily in Pakistan. Large scale patterns connected with these world wide features will begin allowing for more tropical waves to exit Africa without running into the larger than normal dry air of the Saharan Air Layer (SAL) that has been so prevelant the last 2 months. The areal coverage of the SAL has decreased in the last several days and the area near the coast of Africa is more moist. This means that there will less new dust and dry air moving off the continent as move rain laden air with the tropical waves move west.

The tropical wave in the Caribbean is causing gusty winds and an increase in surf even along the northeast coast of Puerto Rico. Our Luquillo, PR web cam below shows the large swells breaking on the beach today. 

Satellite data from the European Space Agency’s METEOSAT satellite shows that in addition to the two tropical waves that have moved off of Africa, there are 2 convective cluster inland in Africa waiting in the wings to emerge off of the African continent. This is another sign that an active period is likely in late August and into September.

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T.D. #5 Déjà vu

Posted by Andy Johnson under Daily updates

The center of lowest pressure and the circulation center of the remains of Tropical Depression #5 have re-emerged in the Gulf of Mexico southwest of Panama City, FL. The surface circulation is well defined as seen in the streamline analysis below. Hurricane reconnaissance aircraft will fly into the disturbance this afternoon to investigate whether or not it has once again become a depression. The circulation center has been forced to move south and southwest by upper level steering currents out of the northeast. The same currents that pushed the circulation center offshore in the warmer Gulf water are also having an inhibiting effect by causing northeasterly shear. As a result today, unlike the past few days, most of the deep convection is offshore since the heaviest rains are on the southwest side of the disturbance. The forecast track keeps the circulation center relatively close to land as it moves southwest, then west, and then northward back into Louisiana. Fortunately, as a result, there is not a large window of opportunity for development before making landfall once again. The circulation is passing over the Deepwater Horizon oil disaster.

The enhanced satellite image below shows that the heaviest convection with the remains of T.D. # 5 are located on the southwest side of the surface circulation center. The reason is due to northeasterly winds in the upper atmosphere circulating around a large high pressure system over Texas.

The wind flow shows below is from 200 MB (approximately 40,000 ft). The large upper level high pressure system that has been causing heat wave conditions over the Southern Plains and the Southeast can be seen centered over Texas and Louisiana. The clockwise flow around the strong high is causing northeasterly flow over the remains of T.D. #5 which has partially exposed the low level center of circulation.  Winds are blowing at 15 to 20 knots out of the northeast over the system.

 The basin-wide satellite image below shows a concentrated area of convection has developed over the southwestern Caribbean. There is a tropical wave moving through the Lesser Antilles which is experincing southwesterly shear. Another wave is moving off the coast of Africa southwest of the Cape Verde Islands and another possible wave is located closer to Africa closer to the latitude of the Cape Verde Islands.

 The tropical wave near the Lesser Antilles is running into an area of dry air. A large area of dry air continues in the eastern Atlantic, although, there are signs that the air is becoming more moist closer to the African continent.

The McIDAS image below continues to show the large dry and dusty Saharan Air Layer (SAL) covering much of the eastern Atlantic. However, as I noted yesterday, the new air coming off of Africa is more moist as can seen in the image below (no red near the African coast).  Worldwide patterns are becoming unblocked which should allow for an active period of Cape Verde type tropical cyclones over the next few weeks.

 The long range GFS model shown below is valid for August 25.  It shows at least one tropical cyclone recurving in the central Atlantic, another possible cyclone in the eastern Atlantic and a third possible one in the southwest Caribbean. Errors are large at this time range but, in general, it seems like we will be entering a very active phase of tropical cyclone activity in late August and September.