Category Archives: Atlantic, Caribbean, and Gulf of Mexico

Atlantic TCs

Tropical Storm Ana Makes Landfall

The center of Tropical Storm Ana officially made landfall at 6:00 a.m. EDT on Sunday near Myrtle Beach, South Carolina.  Ana was officially a tropical storm at the time of landfall with maximum sustained winds of 45 m.p.h.  This is one of the earliest landfalls of a tropical storm in the U.S. in the historical record.  Ana moved inland slowly and it has weakened to a tropical depression.  At 2:00 p.m. EDT on Sunday the center of Tropical Depression Ana was located at latitude 34.1°N and longitude 78.9°W which put it about 30 miles north of Myrtle Beach, South Carolina.  Ana was moving toward the northeast at 5 m.p.h.  The maximum sustained wind speed was 35 m.p.h. and there were gusts to 45 m.p.h.  The minimum surface pressure was 1006 mb.  The Tropical Storm Warning for the portion of the coast from South Santee River, South Carolina to Cape Lookout, North Carolina has been discontinued.

The slow movement of Ana is creating the potential for locally heavy rain.  There has been some beach erosion as well, but generally the impacts have been minor.  An upper level trough approaching from the west is expected to steer Ana back out into the Atlantic.  However, strong vertical wind shear and cool Sea Surface Temperatures are expected to prevent significant redevelopment when Ana moves back over water.

Ana Transitions to a Tropical Storm

As Subtropical Storm Ana sat over the relatively warm Sea Surface Temperatures of the Gulf Stream, it drew energy from the upper ocean.  More thunderstorms developed near the center of circulation and condensation released latent energy which warmed the middle and upper levels.  As a result, the circulation became more circularly symmetrical and eventually some upper level outflow developed at the top of the system. As a result of the structural changes, Ana made a transition from a subtropical storm to a tropical storm.

At 11:00 a.m. EDT on Saturday the center of Tropical Storm Ana was located at latitude 32.7°N and longitude 77.9°W which put it about 90 miles southeast of Myrtle Beach, South Carolina and about 105 miles south of Wilmington, North Carolina.  Ana was moving toward the northwest at 3 m.p.h.  The maximum sustained wind speed was 60 m.p.h. and there were gusts to 70 m.p.h.  The minimum surface pressure was 1001 mb.

A Tropical Storm Warning remains in effect from South Santee River, South Carolina to Cape Lookout, North Carolina.  A Tropical Storm Watch is in effect from Edisto Beach to South Santee River, South Carolina.

As the high pressure system that has been blocking the forward progress of Ana moves eastward, the tropical storm will move toward the coast.  It is likely to make landfall near the border of South Carolina and North Carolina on Sunday morning.  An upper level trough approaching from the west will turn Ana toward the northeast and sweep it out to sea after it makes landfall.

Ana is still over the relatively warm water of the Gulf Stream and it is likely to maintain its intensity on Saturday.  When Ana moves north of the Gulf Stream, it will cross over cooler water.  In addition, the approaching upper level trough will begin to generate some vertical wind shear over Ana.  The effects of cooler water and more wind shear mean that Ana will likely be weakening as it approaches the coast.  It will bring some wind, locally heavy rain and beach erosion, but the impacts should be minor in most locations.

Tropical Storm Warning Issued for Ana

The National Hurricane Center has issued a Tropical Storm Warning for the portion of the coast from South Santee River, South Carolina to Surf City, North Carolina.  A Tropical Storm Watch remains in effect from Edisto Beach to South Santee River, South Carolina and from Surf City to Cape Lookout, North Carolina.

At 11:00 a.m. EDT on Friday the center of Subtropical Storm Ana was located at latitude 31.5°N north and longitude 77.3°W which put it about 250 miles east of Savannah, Georgia, about 190 miles east-southeast of Charleston, South Carolina and about 180 miles south-southeast of Wilmington, North Carolina.  Ana was nearly stationary.  The maximum sustained wind speed was 45 m.p.h. and there were gusts to 60 m.p.h.  The minimum surface pressure was 1001 mb.

Thunderstorms are forming on the southern and eastern sides of the circulation and Ana is beginning to look more like a tropical cyclone on satellite images.  It could slowly make a transition to a tropical storm during the next several days.

A high pressure system north of Ana is expected to move slowly eastward and steer Ana toward the coast during the next two or three days.  After that time an upper level trough approaching from the west is expected to steer Ana to the northeast and out to sea.

A combination of marginal Sea Surface Temperatures, drier air and some vertical wind shear is expected to limit the potential for intensification.  However, some modest intensification is possible and the surface pressure has decreased slightly in recent hours.

 

Subtropical Storm Ana Forms Off Southeast U.S. Coast

Thunderstorms developed closer to a broad area of low pressure off the southeast U.S. coast and the National Hurricane Center (NHC) classified it as Subtropical Storm Ana.  At 11:00 p.m. EDT on Thursday the center of Subtropical Storm Ana was located at latitude 31.5°N and longitude 77.6°E which put it about 250 miles east of Savannah, Georgia, about 180 miles southeast of Charleston, South Carolina and about 200 miles south of Wilmington, North Carolina.  Ana was moving toward the north at 2 m.p.h.  The maximum sustained wind speed was 45 m.p.h. and there were gusts to 60 m.p.h.  The minimum surface pressure was 1004 mb.  A Tropical Storm Watch has been issued for the portion of the coast from Edisto Beach, South Carolina to Cape Lookout, North Carolina.

More thunderstorms are being generated near the center of circulation, but the strongest winds are about 90 miles from the center.  So, the structure does not match a classical tropical cyclone where the strongest winds are closer to the center and NHC classified it as a subtropical storm.  The center of circulation is over Sea Surface Temperatures (SSTs) near 26°C which are warm enough to support the development of a tropical cyclone.  So, Ana could make a transition to a tropical storm during the next 24 to 48 hours.  The upper level winds are lighter and vertical wind shear has decreased.  However, because of the proximity to the coast some drier air is being pulled around the western side of the circulation.  Only modest intensification is expected due to marginal SSTs, some vertical wind shear and drier air.

A high pressure system north of Ana is likely to limit the motion of Ana for the next day or two.  Eventually, the high will shift eastward and an upper level trough approaching from the west will accelerate Ana toward the northeast.  Persistent northeasterly winds along the coast could create problems with beach erosion.  The slow movement also means some locations could receive locally heavy rainfall.

 

Possible Development of Low Pressure East of Florida on Wednesday

A number of numerical models have been predicting the development of some type of low pressure system east of Florida this week.  The surface pressure has decreased by about 4 mb during the past 24 hours at several locations in the northern Bahamas, which could be an early sign that a surface low is in the formative stages.  When the low forms, it will likely be classified as either an extratropical cyclone (a typical mid-latitude low with a cold core) or a subtropical cyclone (a type of hybrid low with some tropical characteristics).  An upper level trough over the eastern Gulf of Mexico is generating strong southwesterly winds across the region.  At the same time a surface high pressure system north of the area is producing northeasterly winds in the lower levels.  The combination of southwesterly winds in the upper levels and northeasterly winds in the lower levels means the vertical wind shear over the likely development region is very high.  Since tropical cyclones form in regions of little vertical wind shear, the low is not likely to be a tropical cyclone when it develops.

However, the surface high north of the system is likely to inhibit the northward motion of the low.  If the low moves slowly while it is over warm Sea Surface Temperatures, the thunderstorms in the circulation could release enough latent energy to warm the upper levels of the circulation.  If, at the same time, an upper level ridge over the Central U.S. moves eastward and causes the upper level wind speed to diminish, then the wind shear over the low could be reduced.  Less shear and warmer temperatures in the upper levels could cause the structure of the low to taken on a more tropical form.  It is possible that it could make a transition to a tropical cyclone if the environment is just right.

The forecast track of the low is uncertain because it is unknown precisely where the low will form initially.  It does appear that after the low forms it will move northward slowly for several days.  The expected track could bring the low near the Mid-Atlantic Coast by the end of the week.  Given the Sea Surface Temperatures, the wind shear, and the time of year, the low is likely to be be of tropical storm strength by the end of the week.  However, both the track and intensity forecasts will be highly uncertain until the low pressure system organizes.  Even if the center of the low stays off the coast, northeasterly winds at the surface could generate some beach erosion.

Center of Former Tropical Storm Hanna Emerges Over Gulf of Honduras

The center of former Tropical Storm Hanna moved steadily toward the west-northwest during the past 18 hours and it recently moved off the coast of Honduras and out over the Gulf of Honduras near Roatan Island.  At 3:00 p.m. EDT the center of Tropical Depression Hanna was located at latitude 16.5°N and longitude 87.0°W which put it just west of Roatan Island, about 140 miles east-southeast of Belize City, Belize and about 710 miles south-southwest of Key West, Florida.  Hanna was moving toward the west-northwest at 7 m.p.h.  The maximum sustained wind speed was 35 m.p.h. and the minimum surface pressure was 1009 mb.

Hanna has a tight, well developed core and thunderstorms are beginning to grow near the center of circulation.  The upper level winds over Hanna are light and the Sea Surface Temperatures in the Gulf of Honduras are quite warm.  The environment is favorable for intensification, although proximity to land could inhibit strengthening.  Hanna probably only has another 12-24 hours to intensify before it makes landfall in Belize, but some intensification is definitely possible.

Clockwise flow around a mid-level ridge of high pressure passing north of Hanna is steering it toward the west-northwest and this general motion is expected to continue.  On it’s current track, Hanna will make landfall on the coast of Belize on Wednesday.

Tropical Storm Hanna Forms Near Nicaragua and Honduras

A low pressure system formerly designated as Tropical Depression Nine intensified and it has been classified as Tropical Storm Hanna.  At 11:00 a.m. EDT on Monday the center of Tropical Storm Hanna was located at latitude 14.5°N and longitude 83.2°W which put it about 35 miles north-northeast of Puerto Cabezas, Nicaragua, about 35 miles south of Cabo Gracias a Dios and about 800 miles south-southwest of Key West, Florida.  Hanna was moving toward the west-southwest a 7 m.p.h.  The maximum sustained wind speed was 40 m.p.h. and the minimum surface pressure was 1005 mb.  A Tropical Storm Warning has been issued for the portion of the coast from Puerto Cabezas, Nicaragua to Punta Patuca,, Honduras.

The low pressure system that was once designated Tropical Depression Nine moved southeastward during the weekend.  It eventually moved far enough south to get away from stronger westerly winds to its north and drier air flowing southward over the northwestern Caribbean Sea.  As a result thunderstorms developed near the center of the low and it began to intensify.  Hanna is very close to the coast of Nicaragua and it has a limited time period to intensify before the center moves onshore.

An upper level ridge moving north of Hanna is steering it west-southwestward.  As the upper level ridge moves east, Hanna could turn more toward the west or even west-northwest.  The center of Hanna could move very near the coast of Honduras during the next several days.

The greatest threat from Hanna will be potentially heavy rainfall over Nicaragua and Honduras.

 

Former Tropical Depression Nine Moves Over Northwestern Caribbean Sea

A small area of low pressure that was classified as Tropical Depression Nine when it was over the Bay of Campeche crossed the Yucatan peninsula and it is now over the northwestern Caribbean Sea.  At 2:00 p.m. EDT on Friday the low was centered at latitude 19.0°N and longitude 87.0°W which put it about 150 miles south of Cancun, Mexico and about 550 miles south-southwest of Key West, Florida.  The low was moving toward the east-northeast at 9 m.p.h.  The maximum sustained wind speed was 25 m.p.h. and the minimum surface pressure was 1008 mb.

Scattered thunderstorms are forming in the vicinity of the low, but the circulation does not appear to be as well organized as it was 24 hours ago.  However, the low is now over water where the Sea Surface Temperatures (SSTs) exceed 29°C Celsius and it appears to be in an area where the winds is diverging in upper levels.  At the same time, there are stronger upper level winds north of the low and drier air from higher latitudes is north and west of the low.  So, some factors in the environment (warm SSTs and upper level divergence) would support intensification, while other factors (nearby wind shear and drier air) would inhibit intensification.  At the  moment most guidance suggest that there is only about a 15% probability that the low will intensify into a tropical cyclone.

However, some guidance from numerical models also suggests that the low could move slowly eastward during the next 24-48 hours as it is affected by an upper level trough passing to its north.  The guidance then suggests that the low could start to move slowly back to the west as an upper level ridge passes north of it.  If the low spends a few days over the warm water of the northwestern Caribbean Sea, then it has the potential to intensify into a tropical cyclone.

 

Tropical Depression Nine Moving Across Yucatan Peninsula

The center of Tropical Depression Nine (TD9) moved inland last night near Ciudad del Carmen, Mexico and TD9 is moving across the Yucatan Peninsula this afternoon.  At 2:00 p.m. EDT on Thursday the center of TD9 was located at latitude 18.1°N and longitude 90.4°W which put it about 190 miles west-northwest of Belize City, Belize and about 750 miles southwest of Key West, Florida.  TD9 was moving toward the east-southeast at 7 m.p.h.  The maximum sustained wind speed was 25 m.p.h. and the minimum surface pressure was 1007 mb.  TD9 is about midway between the Gulf of Mexico and the northwestern Caribbean Sea and it is possible that the center of TD9 could move over the water on Friday.

The low level circulation around TD9 is still well organized and it is possible to see spiral bands rotating counterclockwise around the center on visible satellite imagery.  Some thunderstorms have developed near the center of circulation this afternoon.  Drier air is flowing southward over the Gulf of Mexico and some of that dry air has reached the northern part of the Yucatan peninsula where it is inhibiting the formation of deep convection.  In addition westerly winds in the upper levels are still creating wind shear over the top of TD9.

The higher probability is that the effects of being over land, drier air and wind shear will cause the lower level circulation of TD9 to spin down and dissipate.  The National Hurricane Center is giving this result a probability of 90%.  However, there is a 10% probability that the center of TD9 moves out over the northwestern Caribbean Sea and begins to intensify.  The Sea Surface Temperatures (SSTs) in the northwestern Caribbean Sea are warmer than 29°C and the warm water is fairly deep.  So, there is plenty of energy to support the intensification of a tropical cyclone if TD9 reaches that area.  In addition, as TD9 moves farther south, it will be getting away from the strongest of the upper level winds and the wind shear will start to decrease.  Water vapor will evaporate into the drier air and so it will gradually get moister and have less of an effect on TD9.

If TD9 makes it to the northwestern Caribbean Sea, it could become stationary for several days.  If that happens, then some intensification will be possible.  Of course, before any intensification can occur, it will require that the center of circulation move back over water.  So, the movement of TD9 during the next 24 hours will determine if it dissipates or has a chance to intensify.

 

Tropical Depression Nine Forms Over Bay of Campeche

More thunderstorms formed near the center of a small low pressure system over the Bay of Campeche and the National Hurricane Center classified the low as Tropical Depression Nine (TD9) at 11:00 p.m. EDT on Tuesday.  The center of TD9 was located at latitude 19.4°N and longitude 92.9°W which put it about 160 miles west of Campeche, Mexico and about 850 miles west-southwest of Key West, Florida.  TD9 was moving toward the east at 6 m.p.h.  The maximum sustained wind speed was 35 m.p.h. and the minimum surface pressure was 1000 mb.  The government of Mexico has issued a Tropical Storm Warning for the portion of the coast from Celestun to Frontera.

Westerly winds in the upper levels are still creating wind shear over the top of TD9 and most of the thunderstorms are located in the eastern half of the circulation.  However, the upper level wind speed is expected to diminish and TD9 is likely to intensify into Tropical Storm Hanna on Wednesday.  The westerly winds are also likely to continue to push TD9 toward the east or east-northeast during the next 24 hours.