Category Archives: Atlantic, Caribbean, and Gulf of Mexico

Atlantic TCs

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.

 

Potential Tropical Cyclone Developing Over Bay of Campeche

A reconnaissance plane found a small center of low pressure within a broader area of low pressure over the Bay of Campeche on Tuesday afternoon.  The plane also found winds to near tropical storm force.  At the 3:00 p.m. EDT the low was centered at latitude 19.3°N and longitude 93.7°W which put it about 350 miles northwest of Campeche, Mexico and about 850 miles west-southwest of Key West, Florida.  The low was moving toward the east at 6 m.p.h.  The maximum sustained wind speed was 38 m.p.h. and the minimum surface pressure of 1001 mb.

Thunderstorms are forming mainly on the southern and eastern sides of the center.  The low could be pulling in some of the drier air over the northern Gulf of Mexico, which may be limiting convection on the northwest side of the low.  Westerly winds in the upper levels are also generating wind shear, which is inhibiting the development of the low.  On the other hand, the low is over Sea Surface Temperatures (SSTs) that are warmer than 29°C and there is plenty of energy in the ocean to support the development of a tropical cyclone.  The pressure has fallen about 5-6 mb in the past 12 hours and so the low appears to be getting stronger.  If more thunderstorms form around the center of the low, it could be classified as a tropical depression or a tropical storm.

The westerly winds in the upper and middle levels are pushing the low slowly toward the east.  Guidance from the forecast models seems to be divided into two main possibilities.  One group of models keeps the low relatively weak and forecasts it to move eastward across the Yucatan peninsula and into the northwestern Caribbean Sea before turning it northeastward and moving the low across the Bahamas.  A second group of models predicts that the low will be a bit stronger and that the upper level flow will turn it northeastward sooner and move the low across southern Florida.  If that second scenario occurs, the low could bring stronger winds and heavy rainfall to parts of south Florida.

 

Possible Tropical Development Over Southern Gulf of Mexico

A low pressure system has formed at the surface along the western end of a stationary front over the Bay of Campeche.  It is possible that this low pressure system could intensify into a tropical cyclone and the National Hurricane Center has tasked a reconnaissance plane to investigate the low tomorrow, if necessary.  At 8:00 a.m. EDT on Monday the low was centered at latitude 19.5°N and longitude 95.5°W which put it about 50 miles east of Veracruz, Mexico and about 940 miles west-southwest of Key West, Florida.  The low as moving toward the northeast at 3 m.p.h.  The maximum sustained wind speed was 30 m.p.h. and the minimum surface pressure was 1008 mb.

The low is over Sea Surface Temperatures (SSTs) that are warmer than 29°C and the southern Gulf of Mexico is a location where we see tropical cyclones develop late in the hurricane season.  On the other hand, westerly winds in the upper levels are creating wind shear over the low pressure system and there is drier air over the northern half of the Gulf of Mexico.  Those two factors will inhibit intensification of the system and so tropical development of the low could be slow.  If thunderstorms do develop near the center of the low, it will remain over warm SSTs while it is in the Gulf of Mexico and it could become a tropical storm.

There is westerly flow in the middle and upper levels over the Gulf of Mexico and that flow is likely to push the low pressure system toward the east.  The low could move slowly during a period while it is organizing.  If an area of deep thunderstorms forms, then the middle and upper level winds could push the low eastward more quickly.  The low could approach southwestern Florida later this week.

 

Eyewall of Hurricane Gonzalo Is Rapidly Approaching Bermuda

The northern eyewall of Hurricane Gonzalo is approximately 45 miles (72 km) south-southwest of Bermuda.  The strongest winds in a tropical cyclone are normally found in the eyewall and so the weather conditions over Bermuda are likely to deteriorate rapidly during the next few hours.  At 5:00 p.m. EDT the weather station on Bermuda was reporting easterly winds at 45 m.p.h. with gusts to 67 m.p.h.  Heavy rain was falling and the pressure was falling rapidly.  Based on the current motion of Gonzalo, hurricane force winds could reach Bermuda during the next two or three hours.

At 5:00 p.m. EDT the center of Hurricane Gonzalo was located at latitude 31.7°N and longitude 65.3°W which put it about 50 miles southwest of Bermuda.  The maximum sustained wind speed was 115 m.p.h. and the minimum surface pressure was 949 mb.  A Hurricane Warning remains in effect for Bermuda.  The Canadian Hurricane Center has issued a Tropical Storm Watch that extends from Arnolds Cove to Chapels Cove, Newfoundland.

As of 5:00 p.m. EDT the maximum sustained wind speed in Gonzalo was 115 m.p.h.  Southwesterly winds in the upper levels are creating wind shear over Gonzalo, but it is still likely to strike Bermuda as a major hurricane.  A storm surge and wave action could pose a significant risk to the south coast.  High winds could also do damage, especially to exposed structures at higher elevations.