Category Archives: Atlantic, Caribbean, and Gulf of Mexico

Atlantic TCs

Tropical Storm Danny Heading West

Tropical Storm Danny has moved steadily westward during the past 24 hours.  At 11:00 a.m. EDT on Wednesday the center of Tropical Storm Danny was located at latitude 11.2°N and longitude 41.1°W which put it about 1385 miles (2235 km) east of the Lesser Antilles and about 2740 miles (4410 km) east-southeast of Miami, Florida.  Danny was moving toward the west at 12 m.p.h. (19 km/h).  The maximum sustained wind speed was 50 m.p.h. (80 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 1000 mb.

The organization of the circulation of Danny has varied during the past day.  It has a visible tight core at the center, but earlier today there was no convection around the core.  Recent satellite images show new thunderstorms developing near the core.  The environment around Danny is complex and it contains both positive and negative factors.  Danny is currently over water where the Sea Surface Temperature (SST) is near 28°C.  However, there is slightly cooler water just to the north of the tropical storm.  Satellite imagery indicates that there could also be drier air north of the circulation and some of that drier air could be pulled into Danny.  The upper level winds are light and upper level divergence is occurring.  However, a surge in the low level trade winds is about 250 miles (400 km) east of Danny.   If the surge in the trade winds reaches the core of Danny, it could push the lower part of the circulation out ahead (to the west) of the upper part of the circulation.  In that case Danny would weaken.

The complexity of the environment around Tropical Storm Danny makes the intensity forecast challenging.  If the trade wind surge does not reach the core of Danny and it stays over warm SSTs, then gradual intensification is possible.  On the other hand, if Danny moves more northward over cooler SSTs and into drier air, or if the trade wind surge creates more vertical wind shear, then Danny could weaken.

A subtropical ridge to the north of Danny is steering Danny toward the west and a generally west or west-northwest motion is forecast for the next few days.  If Danny is a little stronger, it could move a little farther north, and if it is weaker, it could stay farther south.  On its anticipated track, Danny could approach the Lesser Antilles in four or five days.  Interests in those areas should monitor Danny for future developments.

Tropical Depression 4 Forms over Eastern Atlantic

As the calendar reaches mid-August, the environment over the tropical Atlantic Ocean typically becomes more favorable for tropical cyclone formation.  The Sea Surface Temperature warms and vertical wind shear decreases.  Despite the ongoing El Nino in the tropical Pacific Ocean, we are seeing the typical pattern develop in the Atlantic for this time of year.  A low level circulation within an area of thunderstorms over the eastern Atlantic Ocean became better organized on Tuesday and the National Hurricane Center classified the system as Tropical Depression Four (TD4).  At 11:00 a.m. EDT on Tuesday the enter of Tropical Depression Four was located at latitude 10.6°N and longitude 36.5°W which put it about 1665 miles (2765 km) east of the Windward Islands.  TD4 was moving toward the west at 13 m.p.h. (20 km/h).  The maximum sustained wind speed was 35 m.p.. (55 km/h) and there were wind gusts to 45 m.p.h. (75 km/h).  The minimum surface pressure was 1009 mb.

TD4 is currently in an environment that is favorable for intensification.  The upper level winds are light and the thunderstorms are generating upper level divergence in all directions.  It is currently over water where the Sea Surface Temperature is near 28°C.  As long as TD4 moves westward, it will stay over warmer water and intensification will be likely.  If TD4 were to move more toward the northwest, then it would move over slightly cooler water and less intensification would occur.  Since TD4 is forecast to move west, it is expected to become Tropical Storm Danny, and it could be a hurricane later this week.

A subtropical ridge north of TD4 is steering it toward the west and that steering motion is expected to continue for the next 24 to 48 hours.  Later this week an upper level trough passing north of the ridge is expected to weaken the ridge, which could cause TD4 to move northwesterly for a day or so.  After the upper level trough moves off to the east, the subtropical ridge is forecast to steer TD4 back more toward the west.  On its anticipated track TD4 is expected to be east of the Windward Islands this weekend.

Tropical Storm Claudette Forms Southeast of New England

An area of low pressure off the East Coast of the U.S. rapidly acquired tropical characteristics on Monday and it was classified as Tropical Storm Claudette by the National Hurricane Center.  At 1:00 p.m. EDT on Monday the center of Tropical Storm Claudette was located at latitude 37.4°N and longitude 68.1°W which put it about 290 miles (465 km) south-southeast of Nantucket Island, Massachusetts and about 550 miles (885 km) south-southwest of Halifax, Nova Scotia.  Claudette was moving toward the northeast at 15 m.p.h. (24 km/h).  The maximum sustained wind speed as 50 m.p.h. (85 km/h) and there were gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 1004 mb.

Claudette began as a small low pressure system along a nearly stationary frontal boundary off the East Coast of the U.S.  Moderate wind shear kept the system looking non-tropical for much of the weekend.  The wind shear decreased on Monday morning and as the low moved over the warmer water of the Gulf Stream, thunderstorms developed near the center of circulation.  The stationary frontal boundary dissipated and the system took on a more tropical appearance.  Latent energy released in thunderstorms near the center produced the development of a warm core and some banding developed in the eastern portion of the circulation.  As a result of those changes, the system was classified as Tropical Storm Claudette.

Claudette could strengthen in the short term.  It is still over the Gulf Stream and the upper level winds are not too strong.  However, once the tropical storm moves north of latitude 40°N, it will move over cooler Sea Surface Temperatures.  In addition, stronger upper level winds will increase the vertical wind shear in a day or two.  Claudette could make a transition to an extratropical cyclone within 48 hours.

A combination of a trough approaching the eastern U.S, and a ridge over the Atlantic are expected to steer Claudette toward the northeast.  On its anticipated track, Claudette could approach eastern Nova Scotia in about 24 hours and Labrador in 30 hours.

Tropical Depression Bill Bringing Storms to Lower Ohio Valley

The circulation around Tropical Depression Bill brought strong storms to the Lower Ohio River Valley on Friday.  At 5:00 p.m. EDT on Friday the center of Tropical Depression Bill was located at latitude 37.1°N and longitude 90.1°W which put it about 30 miles (50 km) west of Cape Girardeau, Missouri.  Bill was moving toward the east-northeast at 15 m.p.h. (24 km/h).  The maximum sustained wind speed was 25 m.p.h., but there were higher gusts in thunderstorms.  The minimum surface pressure was 1004 mb.

The circulation around Tropical Depression Bill retained enough tropical characteristics on Friday to be considered a tropical cyclone.  There was still evidence of a warm core in the middle troposphere with a strong center of circulation at the surface and divergent outflow in the upper levels.  Spiral bands of showers and thunderstorms continued to rotate cyclonically around the center, and some thunderstorms approached severe criteria.  A stationary frontal boundary ran from New Jersey across Ohio to central Missouri.  However, the circulation around the tropical depression was south of the boundary and it was clearly a distinct area of low pressure.

Tropical Depression Bill is expected to continue its east-northeasterly motion during the weekend.  It will pass south of Ohio on Saturday and cross New Jersey on Sunday.  The tropical depression will continue to produce locally heavy rainfall and the potential for isolated severe thunderstorms.

Tropical Depression Bill Bringing Rain to Arkansas and Missouri

Tropical Depression Bill continued its slow movement over the South Central U.S. on Thursday and it brought rain to Arkansas and southern Missouri.  At 11:00 p.m. EDT on Thursday the center of Tropical Depression Bill was located at latitude 35.9°N and longitude 93.8°W which put it about 20 miles (30 km) east of Fayetteville, Arkansas.  Bill was moving toward the east-northeast at 10 m.p.h. (16 km/h).  The maximum sustained wind speed was 20 m.p.h. (30 km/h) and the minimum surface pressure was 1005 mb.

Even thought the center of Bill has been over land for more than 48 hours, it retains many of the characteristics of a tropical cyclone.  It has a well defined cyclonic circulation with a warm core in the middle troposphere and there is upper level divergence.  As a result, Bill is still officially classified as a tropical depression.

Bill is moving around the western end of a high pressure system centered over the Atlantic Ocean.  It should continue to move toward the east-northeast during the next several days.  On its anticipated track Bill will bring rain to northern Arkansas and southern Missouri on Friday.  It will move up the Ohio River Valley on Saturday and enhance the rainfall in those areas.  The circulation of the tropical depression could merge with a nearly stationary frontal boundary north of the Ohio River during the weekend.  Heavy rain falling on saturated ground could create the potential for flooding in some areas.

Tropical Depression Bill Crossing Red River Into Oklahoma

Tropical Depression Bill moved northward across north Texas on Wednesday and brought heavy rain to parts of Texas and Oklahoma.  At 11:00 p.m. EDT on Wednesday the center of Tropical Depression Bill was located at latitude 33.7°N and longitude 97.3°W which put it about 65 miles (105 km) north-northwest of Dallas, Texas.  Bill was moving toward the north at 10 m.p.h. (16 km/h).  The maximum sustained wind speed was 30 m.p.h. (50 km/h).  There were wind gusts to 50 m.p.h. (80 km/h) in some thunderstorms.  The minimum surface pressure was 999 mb.

Bill still has a well organized circulation at the surface and throughout the troposphere.  There is still a warm core in the middle troposphere and divergence in the upper levels.  The upper level divergence pumped out the same amount of mass as converged in the lower levels and the surface pressure remained constant on Wednesday.  Some drier air is wrapping around the southern part of the circulation and most of the rain is falling north and east of the center.  The slow movement of Bill has generated significant amounts of rain and flooding is occurring in some parts of Texas and Oklahoma.  A few thunderstorms have also produced damaging wind gusts.

Bill is expected to turn toward the northeast as is moves around the western end of a high pressure system centered off the southeast coast of the U.S.  It will move slowly across Oklahoma on Thursday and across Arkansas on Friday before moving up the Ohio River Valley during the weekend.

 

Tropical Storm Bill Moving Farther Into Texas

Tropical Storm Bill continued to move farther into Texas after making landfall near Matagorda Island on Tuesday.  At 11:00 p.m. EDT on Tuesday the center of Tropical Storm Bill was located at latitude 29.5°N and longitude 97.0°W which put it about 45 miles (70 km) north of Victoria, Texas.  Bill was moving toward the north at 12 m.p.h. (19 km/h).  The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were winds gusts to 50 m.p.h. (85 km/h).  The minimum surface pressure was 1000 mb.  The strongest winds were occurring primarily in a rainband over the Gulf of Mexico.  A Tropical Storm Warning was in effect for the portion of the coast from Port Oconnor to San Luis Pass, Texas.

The circulation around Bill remains well organized and most of the rain is falling north and east of the center.  The circulation will slowly spin down as it moves farther away from the Gulf of Mexico and its supply of moist air is reduced.  Bill is expected to move north and then turn northeast as it moves around the western end of a high pressure system centered off the coast of the southeastern U.S.  The greatest risk will be from locally heavy rain falling on saturated ground in north Texas and Oklahoma.  Flooding may occur in some locations as a result of the heavy rain.  Some of the moisture associated with the tropical storm could be transported over the Ohio River Valley later this week.

Tropical Storm Bills Forms Near Texas

The National Hurricane Center (NHC) classified a low pressure system over the western Gulf of Mexico as Tropical Storm Bill.  At 11:00 p.m. EDT on Monday the center of Tropical Storm Bill was located at latitude 27.1°N and longitude 94.2°W which put it about 160 miles (260 km) east-southeast of Port OConnor, Texas and about 155 miles (250 km) south-southeast of Galveston, Texas.  Bill was moving toward the northwest at 12 m.p.h. (19 km/h).  The maximum sustained wind speed was 50 m.p.h. (85 km/h) and there were wind gusts to 65 m.p.h. (105 km/h).  The minimum surface pressure was 1005 mb.  A Tropical Storm Warning has been issued for the portion of the coast from Baffin Bay to High Island, Texas.

Bill formed as a result of the interaction between a broad surface low pressure system and an upper level low over the Gulf of Mexico.  Thunderstorms began to form near the center of circulation on Monday afternoon and the structure of the system changed to a more tropical cyclone like pattern.  The thunderstorms near the center began to warm the middle and upper troposphere and create a warm core.  The thunderstorms became substantial enough to generate upper level divergence from the core of the circulation and NHC classified it as Tropical Storm Bill.  Bill is moving over water where the Sea Surface Temperature (SST) is near 29°C.  The vertical wind shear over the system decreased on Monday and Bill has a few hours during which it could intensify before it makes landfall in Texas.

An upper level ridge over the southeastern U.S. is steering Bill northwestward toward the coast of Texas and that motion is expected to continue.  Bill is expected to make landfall in Texas on Tuesday.  Although Bill will bring some wind when it makes landfall, heavy rainfall will be the biggest hazard.  Heavy rain on top of wet soils will create the potential for new flooding in some locations, especially in Texas and Oklahoma.  Winds blowing toward the coast will also create some water level rises and Coastal Flood Warnings and Advisories have been issued for portions of the coast of Texas and Louisiana.

Low Pressure Organizing Over the Southern Gulf of Mexico

A complex low pressure system over the southern Gulf of Mexico is showing signs of greater organization.  A reconnaissance aircraft investigated the system on Sunday afternoon and found evidence of a broad area of low pressure at the surface and winds to tropical storm force northeast of the low.  The official designation for this system is Invest 91L.  At 11:00 p.m. EDT on Sunday night the approximate center of the broad low was located at latitude 22.7°N and longitude 90.2°W which put it about 540 miles (870 km) south-southeast of Galveston, Texas and about 540 miles (870 km) east-southeast of Brownsville, Texas.  The low was moving toward the northwest at 14 m.p.h. (23 km/h).  The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were gusts to 50 m.p.h. (80 km/h).  The minimum surface pressure was 1007 mb.

Invest 91L is a complex system which includes an upper level low over the southern Gulf of Mexico and a broad area of low pressure at the surface.  Clusters of thunderstorms are forming intermittently east and north of the center of circulation.  The pressure gradient between a strong high pressure system centered over the Atlantic Ocean and the developing surface low is causing the strongest winds to be found in the northeastern part of Invest 91L.  The upper level low is causing the system is to exhibit a more subtropical mode of formation rather a typical tropical genesis.  However, more thunderstorms are beginning to develop closer to the center of circulation and the National Hurricane Center is giving Invest 91L an 80% chance of becoming a tropical cyclone.  The low is moving over water where the Sea Surface Temperature (SST) is around 27°C to 28°C, which is warm enough to support the development of a tropical cyclone.  The upper level low was generating vertical wind shear, but if the surface low develops under the center of the upper low, then the wind shear will have less of an effect.  If more thunderstorms form near the center of circulation and a warm core develops, then the low could be classified as a tropical storm on Monday.  Some intensification is possible because of the warm SSTs.

An upper level ridge centered over the southeastern U.S. is expected to steer the system toward the northwest and it could make landfall on the coast of Texas in 24 to 48 hours.  The primary risk will be locally heavy rainfall, although a minor storm surge could occur in some coastal locations.

Possible Tropical Development in Western Gulf of Mexico

An area of showers and thunderstorms near the Yucatan Peninsula has shown signs of a cyclonic circulation, although the rotation may be in the middle troposphere and not at the surface.  The formal designation of this system is Invest 91L.  At 2:00 p.m EDT on Saturday the center of Invest 91L was located at latitude 20.0°N and longitude 88.4°W which put it about 100 miles (165 km) southeast of Merida, Mexico and about 760 miles (1220 km) south-southeast of Galveston, Texas.  Invest 91L was moving toward the northwest at 5 m.p.h. (8 km/h).  The maximum sustained wind speed was 35 m.p.h. (55 km/h) and there were wind gusts to 45 m.p.h. (70 km/h).  The minimum surface pressure was 1009 mb.  The National Hurricane Center is now giving Invest 91L a 50% chance of developing into a tropical depression or tropical storm in the next five days.  An additional reconnaissance plane has been scheduled to investigate it on Sunday afternoon.

The circulation of Invest 91L is not very well organized.  Almost all of the showers and thunderstorms are occurring in the eastern half of the circulation.  Visible satellite images indicate a possible center of cyclonic rotation over the Yucatan peninsula, but it is not clear if the rotation extends all of the way down to the surface.  Counterclockwise winds around an upper level low over the Gulf of Mexico are generating significant vertical wind shear over Invest 91L.  However, the upper level winds east of the upper low are diverging, which is enhancing rising motion and is supporting the development of the showers and thunderstorms in that area.  The upper level divergence is also causing the surface pressure to decrease slowly, which could lead to the formation of a surface center of low pressure.

When Invest 91L moves into the southern Gulf of Mexico, it will move over water where the Sea Surface Temperature is near 27°C to 28°C.  So, there is sufficient energy in the upper ocean to support the development of a tropical cyclone.  The key factor will be the interaction between the upper low and any surface center that forms.  If the surface center forms too close to the upper low, then vertical wind shear will likely inhibit development and the system will remain fairly weak.  If the surface low develops a little farther southeast of the upper low, then there will be less shear and more upper level divergence.  That could allow for more intensification.

Invest 91L is expected to move with the upper low as the upper low moves northward.  Most guidance from numerical models moves the system toward the north-northwest toward the Upper Texas Coast.  However, there will be above normal uncertainty in the track until a well defined center of circulation forms at the surface.

Interests in the western Gulf of Mexico should monitor the progress of Invest 91L.