Tag Archives: Florida

Tropical Storm Hermine Strengthens, Hurricane Warning Issued

Tropical Storm Hermine strengthened on Wednesday evening and a Hurricane Warning was issued for a portion of the northern Florida coast.  A Hurricane Warning was in effect for the portion of the coast from Suwannee River to Mexico Beach, Florida.  A Hurricane Watch and a Tropical Storm Warning was in effect for the portions of the coast from Anclote River to Suwannee River and from Mexico Beach to Destin, Florida.  The Tropical Storm Watch was extended farther up the Mid-Atlantic coast.  The Tropical Storm Watch was in effect for the portion of the coast from Marineland, Florida to South Santee River, South Carolina.

At 11:00 p.m. EDT on Wednesday the center of Tropical Storm Hermine was located at latitude 25.8°N and longitude 87.0°W which put it about 295 miles (475 km) south-southwest of Apalachicola, Florida.  Hermine was moving toward the north-northeast at 10 m.p.h. (16 km/h).  The maximum sustained wind speed was 60 m.p.h. (95 km/h) and there were wind gusts to 75 m.p.h. (120 km/h).  The minimum surface pressure was 998 mb.

The circulation of Tropical Storm Hermine became better organized on Wednesday, but it is still not really well organized.  A tighter center of circulation developed.  However, the wind field is still asymmetrical.  The stronger winds are mainly east of the center and the winds are weaker in the western half of the circulation.  An area of strong thunderstorms developed near the center and another cluster of thunderstorms persisted southwest of the center.  There are not many thunderstorms northwest of the center.  There are some spiral rainbands, but they are fragmented.

Tropical Storm Hermine is in an environment that is favorable for intensification.  It is moving over water where the Sea Surface Temperature is near 30°C.  The upper level flow pattern is enhancing the divergence of mass to the northeast of Hermine.  The enhanced upper level divergence pumped out enough mass to allow the surface pressure to decrease by a few millibars on Wednesday evening.  Tropical Storm Hermine is expected to continue to intensify on Thursday and it should become a hurricane before it makes landfall on Thursday night.

The upper level ridge that was blocking a northward motion of Hermine has weakened.  So, the tropical storm has begun to more toward the north-northeast.  An upper level trough is expected to steer Hermine a little faster toward the northeast on Thursday.  On its anticipated track Hermine could make landfall somewhere between Apalachicola and Tarpon Springs, Florida on Thursday night.  After it moves across northeast Florida, Hermine could move near the coast of Carolinas on Friday.

Hermine is likely to be a hurricane when it makes landfall on Thursday night.  The core of the circulation which will contain the highest winds is likely to be fairly small and Hermine is likely to cause localized minor wind damage.  There will undoubtedly be power outages.  The coastline around the northeastern Gulf of Mexico is vulnerable to storm surges and Hermine will also produce a storm surge which could range up to 7 to 8 feet (2 to 2.5 meters) near where the center crosses the coast.  The storm surge will be less farther away from where the center makes landfall.  In addition Hermine will generate locally heavy rain which could cause fresh water flooding.  Directional wind shear associated with rainbands moving inland could spin up tornadoes in the eastern half of Hermine.

Tropical Depression Nine Causes Hurricane Watch for Part of Florida

Although Tropical Depression Nine did not strengthen on Tuesday afternoon, guidance from numerical models suggested it could be stronger when it eventually reaches the coast of Florida.  As a result, the National Hurricane Center at 5:00 p.m. EDT issued a Hurricane Watch for the portion of the Florida coast from Anclote River to Indian Pass.  A Tropical Storm Watch was issued for the portion of the coast from Indian Pass to the Walton County/Bay County line.

At 5:00 p.m. EDT on Tuesday the center of Tropical Depression Nine was located at latitude 24.4°N and longitude 87.3°W which put it about 345 miles (555 km) west of Key West, Florida.  It 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 1004 mb.

The circulation of Tropical Depression Nine is not currently well organized.  The surface center is located northwest of an apparent mid-level center.  Upper level divergence is not well developed.  The development of thunderstorms has been cyclical during the past several days.  Clusters of thunderstorms developed south and east of the center and then they weaken.  A few hours later more thunderstorms would develop, persist for a few hours and weaken again.  It appears that new thunderstorms are developing northeast and southwest of the surface center which would be a change from the previous pattern.

The vertical structure of Tropical Depression Nine has been out of sync.  As mentioned above, the surface center was northwest of the mid-level center.  Both the surface and mid-level centers have been located on the western edge of a larger upper level high.  Clockwise flow around the upper high has been creating vertical wind shear, which has prevented the development of a vertically coherent structure in the depression.  Despite the effect of the wind shear and the lack of a coherent vertical structure, the surface center has managed to persist and become a little more organized each day.

Tropical Depression Nine is moving through an environment that is currently marginal for intensification.  It is moving over water where the Sea Surface Temperature is near 31°C.  So, there is plenty of energy in the upper ocean.  The vertical wind shear mentioned previously is the primary factor inhibiting intensification.  However, as Tropical Depression Nine moves north, if is forecast to move into an area where the upper level winds are not as strong.  If that happens, then the depression will strengthen.  As the depression becomes more organized, the rate of intensification could increase and the depression could become a hurricane over the northeastern Gulf of Mexico.

An upper level ridge over the southeastern U.S. has been blocking the northward movement of Tropical Depression Nine.  An upper level trough approaching from the west is expected to weaken the ridge.  As the ridge weakens, The depression will be able to move north.  Eventually in a couple of days, the upper level trough is expected to steer the depression more toward the northeast.  On its anticipated track the depression could be approaching the northeastern Gulf Coast by Thursday afternoon.

The northeastern Gulf Coast is very susceptible to storm surges and a surge is the greatest risk.  Locally heavy rain could cause some flooding, and there could be some minor wind damage.

Tropical Depressions Form South of Key West & Southeast of Cape Hatteras

Two tropical depressions formed near the U.S. on Sunday.  Tropical Depression Nine formed south of Key West, Florida and Tropical Depression Eight formed southeast of Cape Hatteras, North Carolina.  Both depressions could have an impact on the U.S., but Tropical Depression Nine could pose a greater risk to the southeastern U.S.

At 5:00 p.m. EDT on Sunday the center of Tropical Depression Nine was located at latitude 23.7°N and longitude 81.7°W which put it about 60 miles (95 km) south of Key West, Florida.  It was moving toward the west at 9 m.p.h. (15 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.

At 5:00 p.m. EDT on Sunday the center of Tropical Depression Eight was located at latitude 31.8°N and longitude 70.9°W which put it about 355 miles (570 km) southeast of Cape Hatteras, North Carolina.  It was moving toward the west at 9 m.p.h. (15 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 1010 mb.

The circulation of Tropical Depression Nine is still organizing.  A NOAA plane found a distinct center of circulation, but most of the stronger thunderstorms are south and east of the center.  There is a broader counterclockwise rotation with numerous showers and thunderstorms indicated by the National Weather Service radar in Key West.  An upper level low east of Florida is contributing to easterly winds that are blowing across the northern side of the depression.  The vertical wind shear is inhibiting the development of thunderstorms north and west of the center.

The circulation of Tropical Depression Eight was more well organized earlier today.  Strong easterly winds from the same upper level low that is affecting Tropical Depression Nine are creating significant vertical wind shear.  Those winds and the shear they caused blew the upper portion of the depression’s circulation west of the low level center of circulation.  The low level circulation is presently exposed as seen on visible satellite imagery and by an Air Force Reserve Hurricane Hunter aircraft.

The intensity forecast for Tropical Depression Nine is challenging because it is moving through a complex environment.  The depression is moving over water where the Sea Surface Temperature is near 31°C.  So, there is plenty of energy in the upper ocean.  However, as mentioned above, an upper low is causing vertical wind shear which will inhibit intensification.  Tropical Depression Nine could move into a region where there is less shear when it moves over the Gulf of Mexico.  Tropical Depression Nine has a good chance to intensify into a tropical storm, but it is unclear if it could become a hurricane before it reaches the coast.

There is also significant uncertainty in the track forecast for Tropical Depression Nine.  A ridge over the southeastern U.S. is steering the depression toward the west and that general motion should continue for several more days.  The ridge is forecast to weaken during the middle of the week and that should allow Tropical Depression Nine to turn toward the north.  The timing of that turn and how sharp it will be are still uncertain.

The upper low is expected to continue to generate wind shear over Tropical Depression Eight.  If the upper levels winds remain as strong as they are now, the depression will slowly weaken.  If the upper level winds weaken, then Tropical Depression Eight could strengthen into a minimal tropical storm.  The upper level low is steering the depression west and that general motion is expected to continue in the short term.  The depression could stall just off the coast of North Carolina.

Tropical Depression Nine could intensify and bring wind and rain to the Gulf Coast later this week.  The Gulf Coast is also vulnerable to storm surges.  Given the uncertainty in both the track and intensity, interests along the coast should monitor official sources of information for updates on Tropical Depression Nine.  The primary effects of Tropical Depression Eight are likely to be higher than normal surf, rip currents and some beach erosion along the North Carolina coast.  People along the Mid-Atlantic coast should pay attention to the depression in case the forecast changes.

Tropical Storm Colin Near Landfall in Florida

Tropical Storm Colin accelerated toward the northeast on Monday afternoon and the center of circulation is about to make landfall near Steinhatchee, Florida.  At 11:00 p.m. EDT on Monday the center of Tropical Storm Colin was located at latitude 29.8°N and longitude 83.8°W which put it about 65 miles (105 km) northwest of Cedar Key, Florida.  Colin was moving toward the northeast at 22 m.p.h. (35 km/h).  The maximum sustained wind speed was 50 m.p.h. (80 km/h) and there were wind gusts to 65 m.p.h. (105 km/h).  The minimum surface pressure was 1001 mb.

A Tropical Storm Warning is in effect for the portion of the coast from Indian Pass to Englewood, Florida.  A Tropical Storm Warning is also in effect for the East Coast from Sebastian Inlet, Florida to Oregon Inlet, North Carolina.

Although Tropical Storm Colin looked ragged on satellite and radar imagery, the pressure did drop to 1001 mb on Monday.  Colin is a very asymmetric tropical storm.  Almost all of the rain and stronger winds are in the eastern half of the circulation.  Most of the heavier rain is falling in bands southeast and northeast of the center.  An upper level trough over Mexico is producing strong southwesterly winds which are blowing over the western half of Colin.  Despite significant vertical wind shear, the center of circulation became more well defined on Monday.  There are few thunderstorms near the center and Colin is clearly a sheared tropical cyclone.

Tropical Storm Colin did produce minor storm surges along the west coast of Florida where the winds pushed the water toward the coast.  Local coastal flooding occurred, especially in the most surge prone areas.  In addition Tropical Storm Colin produced heavy rainfall over the peninsula of Florida.

Normally, a tropical storm weakens when it moves over land because there is more friction and it is removed from its energy source.  However, Tropical Storm Colin could move into a region where there is more upper level divergence.  If the upper level divergence pumps out more mass, the surface pressure could fall and the wind speeds could increase a little bit.  In addition, if Colin moves toward the northeast more quickly then the effect of vertical wind shear will be less.  The wind speed in Tropical Storm Colin is forecast to increase a little on Tuesday, even though it could start to lose its tropical characteristics.

The upper level trough should continue to steer Tropical Storm Colin toward the northeast on Tuesday.  It is expected to move rapidly across northeast Florida and the center of Colin could emerge over the Atlantic Ocean by Tuesday morning.  The center of Colin is expected to move close to the coast of the Carolinas and it could be east of Cape Hatteras by Tuesday night.

On its anticipated track, the strongest winds should occur over the Atlantic Ocean.  Tropical Storm Colin could contribute to locally heavy rainfall in northeast Florida, extreme southeast Georgia and coastal portions of South Carolina and North Carolina.  Wave action could cause some beach erosion.  Wind damage should be minimal, although some power outages could occur.

Tropical Storm Colin Forms Over Gulf of Mexico and Heads for Florida

A broad area of low pressure over the southern Gulf of Mexico became more organized on Sunday and a U.S. Air Force Reserve Hurricane Hunter reconnaissance aircraft found sustained winds of 40 m.p.h. (65 km/h).  As a result, the National Hurricane Center classified the system as Tropical Storm Colin.  At 11:00 p.m. EDT on Sunday the center of Tropical Storm Colin was located at latitude 23.6°N and longitude 87.8°W which put it about 450 miles (720 km) southwest of Tampa, Florida.  Colin was moving toward the north at 9 m.p.h. (15 km/h).  The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (80 km/h).  The minimum surface pressure was 1003 mb.

A Tropical Storm Warning has been issued for the portion of the coast from Indian Pass to Englewood, Florida.  A Tropical Storm Warning has also been issued for the East Coast from Sebastian Inlet, Florida to Altamaha Sound, Georgia.  A Tropical Storm Watch has been issued for the portion of the coast from Altamaha Sound, Georgia to South Santee River, South Carolina.

The circulation of Tropical Storm Colin is very asymmetrical.  The stronger winds and most of the thunderstorms are east of the center of circulation.  Some rotation in the middle levels in the primary band on the east side of Colin is apparent on satellite imagery.  Winds to tropical storm force are occurring up to 185 miles (295 km) from the center of circulation.  However, the winds are much weaker in the western half of the circulation.

The environment around Tropical Storm Colin is marginal for intensification.  Colin is moving over water where the Sea Surface Temperature is near 28°C to 29°C.  So, there is sufficient energy in the upper ocean to support intensification.  An upper level low near Texas and an upper level ridge east of Colin are combining to produce southwesterly winds that are blowing over the western half of the storm.  Those winds are causing strong vertical wind shear which is preventing the development of thunderstorms in that part of the storm.  Part of the upper level ridge is over the eastern half of the circulation.  The upper level winds are weaker there and there is less vertical wind shear, which is allowing strong thunderstorms to persist in that part of Colin.  The upper level ridge is also enhancing upper level divergence to the east of Tropical Storm Colin.  If a new center of circulation were to form closer to the upper level ridge, then more intensification would be possible.  Colin is likely to intensify somewhat on Monday.

The upper low and upper level ridge are also steering Tropical Storm Colin toward the north.  Those features are expected to turn Colin toward the northeast on Monday.  On its anticipated track Tropical Storm Colin will approach the coast of Florida between Tampa and Apalachicola on Monday evening.  However, if a new center of circulation develops farther east, Colin could make landfall farther south along the coast and earlier on Monday.

Heavy rainfall is the greatest risk with Tropical Storm Colin.  It is pulling very humid air from the Caribbean Sea northward over the eastern Gulf of Mexico.  Tropical Storm Colin could also generate a storm surge of 1-6 feet near where the center makes landfall.  The coast along the northeastern Gulf of Mexico is very susceptible to storm surges and water rises will occur in that area.  Wind damage is likely to be minimal, although power outages may occur.  Some tornadoes could be generated when Colin moves over land.  Locally heavy rain could also fall in portions of the Mid-Atlantic states as the circulation of Tropical Storm Colin interacts with a cold front.

Tropical Storm Colin was named on June 5, which is the earliest date on record on which the third Atlantic Tropical Storm has formed.  During the record setting year of 2005 Tropical Storm (later to become Hurricane) Cindy was named on July 5.

Disturbance Near Yucatan Could Develop Over Gulf of Mexico

A tropical disturbance over the northwestern Caribbean Sea near the Yucatan peninsula is moving northwest and it could develop into a tropical cyclone when it moves over the southern Gulf of Mexico.  The National Hurricane Center (NHC) has designated the disturbance as Invest 93L and NHC is putting the probability of development into a tropical cyclone during the next two days at 80%.  At 8:00 p.m. EDT the center of Invest 93L was located at latitude 18.5°N and longitude 87.5°W which put it about 170 miles (270 km) south of Cancun, Mexico.  Invest 93L was moving toward the northwest at 11 m.p.h. (17 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 1005 mb.

Invest 93L consists of a broad area of low pressure at the surface.  Several bands of thunderstorms are occurring in the eastern and northern parts of the circulation.  There is no well defined center of circulation and there are fewer thunderstorms in the inner portion of the circulation.  The strongest winds are occurring in the bands of thunderstorms north and east of the center.  There is some upper level divergence to the east of Invest 93L.

The environment around Invest 93L is not totally favorable for development.  The Sea Surface Temperature in northwest Caribbean Sea is near 30°C, which means there is plenty of energy in the upper ocean.  However, an upper level low near Texas and an upper level ridge east of Invest 93L are combining to generate strong southwesterly winds that are blowing over the top of the disturbance.  Those winds are creating significant vertical wind shear which is inhibiting the development of Invest 93L.  The upper level ridge is enhancing the upper level divergence to the east of the disturbance which allowed the pressure to fall several millibars on Saturday.  The upper winds are lighter near the axis of the ridge which is why the stronger bands of thunderstorms are persisting in that area.

Invest 93L is forecast to move toward the Yucatan peninsula on Sunday.  If the broad area over low pressure moves over land that will prevent it from developing until it moves back over water.  Numerical models are guiding that the disturbance will develop into a tropical cyclone when the area of low pressure moves over the southern Gulf of Mexico.  The upper level ridge is forecast to extend over the southeastern Gulf and if that happens the wind shear could decrease enough to allow development to occur.  Invest 93L could become a tropical depression or a tropical storm over the Gulf of Mexico.

The southwesterly flow over the Gulf of Mexico is forecast to turn Invest 93L toward the northeast.  On its anticipated track the system could reach the west coast of Florida near Cedar Key late Monday or early Tuesday.  The primary risk is likely to be locally heavy rain.  However, the coast in that area is very susceptible to storm surge and there could be some rise in the water level.  The National Hurricane Center has tentatively tasked a reconnaissance plane to investigate Invest 93L on Sunday, if necessary.

Bonnie Brings Heavy Rain and Flooding to South Carolina

Even though Bonnie weakened to a tropical depression before it made landfall near Charleston, it brought locally heavy rain and flooding to parts of South Carolina and eastern Georgia.  A portion of Interstate 95 was closed due to high water.  At 11:00 p.m. EDT on Sunday the center of Tropical Depression Bonnie was located at latitude 32.8°N and longitude 80.1°W which put it about 5 miles (10 km) west of Charleston, South Carolina.  Bonnie was slowly meandering near the coast.  The maximum sustained wind speed was 30 m.p.h. (50 km/h) and there were wind gusts to 40 m.p.h. (65 km/h).  The minimum surface pressure was 1012 mb.

Strong southeasterly winds in the upper levels generated significant vertical wind shear that weakened Tropical Storm Bonnie to a tropical depression on Sunday morning.  However, the lower level circulation remained relatively intact as Bonnie moved onto the coast near Charleston, South Carolina.  Thunderstorms in a band west of the center of circulation dropped heavy rain in parts of southwestern South Carolina and eastern Georgia.  The heavy rain produced some flooding.

Most of the rain has tapered off to a few narrow bands of showers, which is normal at night when weaker tropical cyclones move inland.  However, daytime heating could destabilize the atmosphere and new thunderstorms could redevelop over land on Monday.  Some of those storms could also produce locally heavy rainfall and cause additional flooding.

The center of Tropical Depression Bonnie has drifted back to near the Atlantic Ocean.  Strong southeasterly winds are still blowing in the upper levels and the vertical wind shear should prevent significant redevelopment even if the center moves back over water.  Proximity to the ocean will make it easier for the circulation to pull in more moisture, which could contribute to heavier rainfall.

A high pressure system over the Atlantic and an approaching cold front will combine to produce southwesterly winds in the lower levels of the atmosphere.  Those low level winds are forecast to steer Tropical Depression Bonnie slowly toward the northeast during the next several days.  On its anticipated track Tropical Depression Bonnie is expected to move slowly along the coast of South Carolina and North Carolina.  The primary risks will be locally heavy rain, flooding and rip currents.

TD 2 Intensifies Into Tropical Storm Bonnie

Tropical Depression 2 intensified into Tropical Storm Bonnie as it passed over the warm waters of the Gulf Stream on Saturday.  At 5:00 p.m. EDT on Saturday the center of Tropical Storm Bonnie was located at latitude 31.1°N and longitude 79.4°W which put it about 120 miles (195 km) south-southeast of Charleston, South Carolina.  Bonnie was moving toward the northwest at 10 m.p.h. (16 km/h).  The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (80 km/h).  The minimum surface pressure was 1008 mb.  A Tropical Storm Warning remains in effect for the coast of South Carolina from the Savannah River to Little River Inlet.

Although the convection in Tropical Depression 2 dissipated when it passed over a region of slightly cooler Sea Surface Temperatures (SSTs) on Friday night, thunderstorms redeveloped and persisted when the system crossed the warmer SSTs in the Gulf Stream on Saturday.  Persistent thunderstorms produced enough increase in the wind speed to intensify Tropical Depression 2 into Tropical Storm Bonnie.

The circulation around Tropical Storm Bonnie is very asymmetrical.  Almost all of the thunderstorms are occurring in the northwestern quadrant of the storm and the strongest winds are being generated in that part of the circulation.  There are mainly thin bands of showers in the rest of the storm.  Winds to tropical storm force extend out about 60 miles (95 km) from the center in the northwest quadrant of Bonnie.

An upper level low over Florida and an upper level ridge over the western Atlantic Ocean are combining to generate southeasterly winds which are blowing over the top of Tropical Storm Bonnie.  Moderate vertical wind shear is contributing to the asymmetrical structure by tilting the circulation toward the northwest.  The wind shear is strong enough to inhibit intensification, but Tropical Storm Bonnie is extracting more energy as it passes over the Gulf Stream.  Bonnie could possibly intensify a little more while it is over the Gulf Stream.

The ridge east of Bonnie is steering the tropical storm toward the northwest and that general motion is expected to continue for another 12 to 24 hours.  An upper level trough approaching the ridge from west and the trough is expected to cause the ridge to weaken.  When the ridge weakens, the steering currents will also weaken.  Tropical Storm Bonnie could stall or meander for several days when that happens.

On its anticipated track the center of Tropical Storm Bonnie will approach the coast of South Carolina on Sunday.  The primary threats are coastal erosion, rip currents and locally heavy rainfall.  Persistent rain could create the potential for fresh water flooding.  Wind damage is likely to be minimal.  However, where the winds blow onshore, they could push water toward the coast and contribute to some coastal flooding.

Tropical Depression 2 Forms, Warning Issued for South Carolina

A reconnaissance plane investigated the system that was formerly designated Invest 91L on Friday afternoon and the plane found that the system had enough tropical characteristics to be classified as Tropical Depression 2 by the National Hurricane Center (NHC).  At 5:00 p.m. EDT on Friday the center of Tropical Depression 2 (TD2) was located at latitude 28.5°N and longitude 74.7°W which put it about 435 miles (695 km) southeast of Charleston, South Carolina.  TD2 was moving toward the west-northwest at 13 m.p.h. (20 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.  A Tropical Storm Warning has been issued for the coast of South Carolina from the Savannah River to Little River Inlet.

The circulation in Tropical Depression 2 became better organized on Friday, but it would not yet be considered well organized.  More thunderstorms formed near the center of circulation and a primary rainband now curls around the the northern and western sides of the center.  However, there are only thin bands of showers in much of the eastern half of the circulation.  With persistent thunderstorms near the core of TD2, it possess enough tropical characteristics to be considered a tropical cyclone.

An upper level low near Cuba and an upper level ridge northeast of TD2 are combining to generate northerly winds over the top of the circulation.  Those winds are causing moderate vertical wind shear.  TD2 will also be moving over slightly cooler Sear Surface Temperatures (SSTs) during the next 12 to 18 hours.  The combination of the vertical wind shear and cooler SSTs could keep TD2 from intensifying much during that time period.  TD2 will move over the warmer SSTs of the Gulf Stream later on Saturday.  The vertical wind shear could also decrease somewhat.  Warmer SSTs and less wind shear could allow TD2 to intensify into Tropical Storm Bonnie later on Saturday.

A ridge northeast of TD2 is steering the tropical depression toward the west-northwest and a general motion in that direction is expected for another 36 to 48 hours.  After about two days the steering currents could weaken.  On its anticipated track TD2/Tropical Storm Bonnie is expected to approach the coast of South Carolina on Sunday.  Coastal erosion, rip currents and locally heavy rain are the primary risks.  Wind damage is likely to be minimal.

 

Invest 91L Slightly Stronger, Moving Toward U.S.

The circulation of the low pressure system designated as Invest 91L strengthened slightly on Thursday.  At 8:00 p.m. EDT on Thursday the center of Invest 91L was located at latitude 27.4°N and longitude 70.9°W which put it about 410 miles (660 km) east-northeast of Great Abaco Island, Bahamas and about 675 miles (1090 km) south-southeast of Charleston, South Carolina.  Invest 91L was moving toward the west-northwest at 10 m.p.h. (16 km/h).  The maximum sustained wind speed was 35 m.p.h. (55 km/h) and there were wind gusts to near 45 m.p.h. (70 km/h).  The minimum surface pressure was 1013 mb.  The center of Invest 91L was near NOAA buoy 41047 which reported observations consistent with those numbers.

The organization of Invest 91L improved slightly on Thursday.  A few thunderstorms formed northeast of the center of circulation and they persisted throughout the day.  However, there are few thunderstorms in other parts of Invest 91L.  The circulation became slightly more circular although it is still elongated.  The surface pressure decreased slowly, but steadily throughout the day.

The environment around Invest 91L is only marginal for intensification.  It is over water where the Sea Surface Temperature is near 26°C to 27°C.  However, an upper level low near Cuba and an upper level ridge near the east coast of the U.S. are combining to create southerly winds over the top of Invest 91L.  Those winds are causing moderate levels over vertical wind shear which is inhibiting the development of the system.  The magnitude of the wind shear decreased during the past 24 hours and it could decrease a little more on Friday as the upper level ridge moves farther east.

If more thunderstorms develop near the center of circulation, the system could be classified as a tropical depression or tropical storm.  The National Hurricane Center (NHC) is indicating that there is an 80% probability that the Invest 91L will become a tropical cyclone or subtropical cyclone within 48 hours.  NHC has tentatively tasked a reconnaissance plane to investigate the system on Friday.

The vertical wind shear is limiting the strongest part of the circulation of Invest 91L to the lower half of the troposphere.  Thus, the system is being steered toward the west-northwest by a surface pressure system over the western Atlantic Ocean.  That general motion is expected to continue with a slow northward turn.  On its anticipated track Invest 91L could approach the southeast coast of the U.S. in 48 to 72 hours.

The primary risks with Invest 91L remain coastal erosion, rip currents and locally heavy rainfall.  Some wind damage will be possible, but it is likely to be minimal.