Tag Archives: AL01

Tropical Depression One Forms East of Florida

Tropical Depression One formed east of Florida on Saturday.  At 5:00 p.m. EDT on Saturday the center of Tropical Depression One was located at latitude 28.4°N and longitude 78.6°W which put it about 125 miles (200 km) east of Melbourne, Florida.  The depression was moving toward the north-northeast 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. (75 km/h).  The minimum surface pressure was 1008 mb.

A Tropical Storm Watch was issued for the portion of the coast from Surf City to Duck, North Carolina including Pamlico and Albemarle Sounds.

Surface observations and data from aircraft reconnaissance indicated that a distinct low pressure system formed east of Florida on Saturday and the National Hurricane Center designated the system as Tropical Depression One.  More thunderstorms developed near the center of circulation.  Storms near the center began to generate upper level divergence which pumped mass away to the east of the depression.  The strongest winds were occurring in the inner part of the circulation, which was consistent with the typical structure of a tropical cyclone.  Bands of showers and thunderstorms were developing.  The strongest bands were in the eastern half of the circulation.

Tropical Depression One will move through an environment favorable for intensification during the next several days.  The depression will move over water where the Sea Surface Temperature is near 25°C.  An upper level trough over the eastern Gulf of Mexico and an upper level ridge east of Florida will interact to produce southerly winds which will blow toward the top of the circulation.  Those winds will cause some vertical wind shear but the shear will not be strong enough to prevent intensification.  Tropical Depression One will strengthen into a tropical storm.

The upper level trough and upper level ridge will steer Tropical Depression One toward the north-northeast during the next 36 to 48 hours.  On its anticipated track Tropical Depression One will approach the coast of North Carolina on Monday.  It will be a tropical storm by that time.  It will bring gusty winds and heavy rain to parts of the coast.  Wind blowing water toward the coast will cause the water level to rise and there will be erosion of the beaches.

Subtropical Storm Andrea Develops Southwest of Bermuda

Subtropical Storm Andrea developed southwest of Bermuda on Monday afternoon.  An Air Force Reserve Hurricane Hunter aircraft investigated an area of low pressure southwest of Bermuda on Monday afternoon.  The aircraft determined that there was a well defined center of circulation at the surface and the National Hurricane Center designated the system as Subtropical Storm Andrea.  At 11:00 p.m. EDT on Monday the center of Subtropical Storm Andrea was located at latitude 29.5°N and longitude 68.7°W which put it about 300 miles (485 km) southwest of Bermuda.  Andrea 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 wind gusts to 50 m.p.h. (80 km/h).  The minimum surface pressure was 1006 mb.

The circulation around Subtropical Storm Andrea was asymmetrical.  Most of the thunderstorms and the strongest winds were occurring northeast of the center of circulation.  Bands in other parts of the circulation consisted primarily of lower clouds and showers and the winds were weaker in those parts of Andrea.  An upper low northeast of the Bahamas was producing southerly winds which were blowing toward the top of the circulation.  Those winds were creating moderate vertical wind shear and the shear was the primary cause of the asymmetrical structure of Subtropical Storm Andrea.  The asymmetrical structure was the reason why Andrea was classified as a subtropical storm.  Winds to tropical storm force extended out about 65 miles (105 km) from the center of Andrea in the northeastern quadrant of the circulation.

Subtropical Storm Andrea will move through an environment marginally favorable for intensification on Tuesday.  Andrea will move over water where the Sea Surface Temperature is near 25°C.  The upper low will continue to cause moderate vertical wind shear, but the low could weaken slightly on Tuesday.  If the upper level winds weaken, then Andrea could get stronger.  Stronger upper level westerly winds could affect Subtropical Storm Andrea on Wednesday.  Those winds will cause stronger vertical wind shear which will weaken Andrea.

The upper level low northeast of the Bahamas will steer Subtropical Storm Andrea toward the north during the next 12-18 hours.  After that time the upper level westerly winds are likely to steer Andrea more toward the east.  On its anticipated track Subtropical Storm Andrea could be near Bermuda in about 36 hours.  Andrea could bring gusty winds and rain showers to Bermuda on Wednesday.

Unusual Tropical Depression Alberto Reaches Michigan

Unusual Tropical Depression Alberto reached southern Michigan on Wednesday as it continued its northward journey from the Gulf of Mexico.  At 11:00 p.m. EDT on Wednesday the center of Tropical Depression Alberto was located at latitude 42.4°N and longitude 85.3°W which put it about 45 miles southwest of Lansing, Michigan.  Alberto was moving toward the north-northeast at 26 m.p.h. (43 km/h).  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 996 mb.

The circulation of Tropical Depression Alberto remained intact even though it had been over land for more than two days.  There was a distinct low level center of circulation.  Several bands of showers and thunderstorms were revolving around the center of circulation.  Storms in the core of the circulation were generating upper level divergence.  Tropical Depression Alberto looked like a tropical cyclone on both satellite and radar imagery.

Gusty winds in some of the bands of showers and thunderstorms caused damage to trees and power lines in Indiana and Ohio.  Most of the damage was minor.  The peripheral parts of the circulation of Tropical Depression Alberto interacted with other weather system to produce bands of heavier rain over parts of the southeastern U.S.  The heavy rain contributed to flooding in several states.

Tropical Depression Alberto will move northeast across the Great Lakes and into Canada on Thursday.  The broader circulation around Alberto will again interact with other weather systems to produce bands of heavier rain.  The potential flooding will exist in several states in the southeastern U.S. and Great Lakes region.

Tropical Depression Alberto Drops Heavy Rain Over Southeast U.S.

Tropical Depression Alberto dropped heavy rain over portions of the southeastern U.S. on Tuesday.  At 11:00 p.m. EDT on Monday the center of Tropical Depression Alberto was located at latitude 36.3°N and longitude 87.5°W which put it about 45 miles (75 km) west-northwest of Nashville, Tennessee.  Alberto was moving toward the north at 16 m.p.h. (26 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. (75 km/h).  The minimum surface pressure was 999 mb.

The core of Tropical Depression Alberto moved northward across Alabama and into Tennessee on Tuesday.  The circulation remained well developed and there was a band of showers and thunderstorms that surrounded most of the center.  Upper air data from Nashville, Tennessee indicated that the system might have a warm core and the Weather Prediction Center called it a Tropical Depression in the 11:00 p.m. EDT advisory.  A large counterclockwise circulation extended all the way to eastern North Carolina.  Bands of showers and thunderstorms were rotating northward in the eastern half of the circulation.

Those bands of showers and thunderstorms were dropping heavy rain as they passed over some locations.  A weather station in Asheville , North Carolina received nearly two inches of rain on Tuesday.  Heavier rain likely fell over parts of the Appalachians where the wind forced the air to rise up the mountains.  There were reports of flooding in several locations and Flash Flood Warnings were in effect for a number of counties in western North Carolina.  The National Weather Service Forecast Office in Greenville-Spartanburg, South Carolina issued a Flash Flood Emergency for areas downstream of the Lake Tahoma Dam in central McDowell County, North Carolina due to imminent failure of the dam.  Flash Flood Watches remained in effect from Georgia to Virginia and westward to the Lower Ohio River Valley.

The core of Tropical Depression Alberto will move northward across Indiana on Wednesday.  Bands of showers and thunderstorms will continue to drop heavy rain in the eastern half of the circulation.  The greatest risk for flooding will be in locations where bands of heavier rain remain over those areas for several hours.  The ground is already very wet in parts of the eastern U.S.  Water levels in streams and rivers could rise quickly.  Saturated ground could also contribute to potential mudslides in steeper terrain.

Subtropical Storm Alberto Makes Landfall in Northwest Florida

Subtropical Storm Alberto made landfall in northwest Florida late on Monday afternoon.  According to the National Hurricane Center the center of Subtropical Storm Alberto officially made landfall near Laguna Beach, Florida.  At 5:00 p.m. the center of Subtropical Storm Alberto was located at latitude 30.3°N and longitude 85.9°W which put it about 15 miles (25 km) west-northwest of Panama City, Florida.  Alberto was moving toward the north at 9 m.p.h. (15 km/h).  The maximum sustained wind speed was 45 m.p.h. (75 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 994 mb.  A Tropical Storm Warning was in effect for the portion of the coast from Aucilla, River, Florida to the border between Florida and Alabama.

Subtropical Storm Alberto weakened slowly as it approached the coast of northwest Florida.  Several factors contributed to the weakening of Alberto.  Drier air spiraled into the core of the circulation.  The drier air inhibited the development of taller thunderstorms in the eastern and southern quadrants of the circulation.  Most of the stronger storms developed north and west of the center of circulation.  Daytime heating of the land made the atmosphere more unstable and the instability contributed to the development of thunderstorms in rainbands in those parts of Alberto.  Subtropical Storm Alberto also mixed cooler water to the surface as it moved slowly toward the coast of Florida.  The Sea Surface Temperature near the coast was about 26°C before Subtropical Storm Alberto arrived.  However, the layer of warmer water was very thin.  The winds caused by Alberto mixed the water in the upper levels of the Gulf of Mexico.  The mixing brought cooler water to the surface and the Sea Surface Temperature cooled to near 24°C.  The cooler water meant there was less energy to support the circulation around Subtropical Storm Alberto.

The circulation of Subtropical Storm Alberto will weaken slowly as it moves inland.  Winds blowing water toward the coast will continue to produce a storm surge of 3 to 4 feet (1 to 1.3 meters) east of the center of circulation for another 12 to 24 hours.  A large surface high pressure system over the Atlantic Ocean will steer Subtropical Storm Alberto slowly toward the north during the next several days.  Locally heavy rain could produce flooding as Alberto moves northward.  Flood Watches have been issued for areas between the Gulf Coast and the Lower Ohio River Valley.  Flood Watches have also been issued for places as far east as the Carolinas and Virginia.  The risk of flooding is even greater for locations that already received heavy rain from previous weather systems.

Subtropical Storm Alberto Strengthens on Its Way to Northwest Florida

Subtropical Storm Alberto strengthened on Sunday as it moved closer to northwest Florida.  At 11:00 p.m. EDT on Sunday the center of Subtropical Storm Alberto was located at latitude 28.5°N and longitude 85.8°W which put it about 95 miles (155 km) south-southwest of Apalachicola, Florida.  Alberto was moving toward the northwest at 9 m.p.h. (15 km/h).  The maximum sustained wind speed was 65 m.p.h. (105 km/h) and the were wind gusts to 80 m.p.h. (130 km/h).  The minimum surface pressure was 991 mb.  A Tropical Storm Warning was in effect for the portion of the coast from Suwannee River, Florida to the border between Alabama and Mississippi.

The circulation of Subtropical Storm Alberto became more organized on Sunday.  A band of showers and thunderstorms wrapped around the center of circulation.  A band of drier air wrapped around the circulation just outside the rainband.  The band of drier air kept the circulation from developing a completely tropical structure and the National Hurricane Center continued to classify Alberto as a subtropical storm.  Alberto moved closer to the center of an upper level low over the Gulf of Mexico.  The upper level winds were weaker near the center of the low and the vertical wind shear decreased.  An upper level ridge over the Florida peninsula enhanced upper level divergence to the east of Alberto and the surface pressure decreases on Sunday.

Subtropical Storm Alberto will move through an environment somewhat favorable for intensification on Monday.  Alberto will move over water where the Sea Surface Temperature is near 28°C.  The upper level low will continue to produce some vertical wind shear.  The band of drier air will limit the development of thunderstorms outside the primary rainband.  Some intensification is possible during the next 12 hours, but the wind shear and drier air should limit any strengthening.

The upper low and the ridge over Florida will steer Subtropical Storm Alberto slowly toward the northwest.  On its anticipated track the center of Subtropical Storm Alberto is expected to make landfall over northwest Florida on Monday.  Alberto will be capable of causing minor wind damage.  Wind blowing water toward the coast will produce a storm surge of up to 4 to 7 feet (1.3 to 2.3 meters).  Alberto will drop heavy rain over parts of the southeastern U.S. and flooding could occur in some locations.

Subtropical Storm Alberto Moves Into the Gulf of Mexico

Subtropical Storm Alberto moved over the southeastern Gulf of Mexico on Saturday.  At 11:00 p.m. EDT on Saturday the center of Subtropical Storm Alberto was located at latitude 23.9°N and longitude 84.6°W which put it about 120 miles (195 km) west-southwest of the Dry Tortugas.  Alberto was moving toward the north-northeast at 13 m.p.h. (20 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 1001 mb.

Tropical Storm Warnings were in effect for the Dry Tortugas and the portions of the coast from Bonita Beach to Anclote River and from the Aucilla River to the border between Alabama and Mississippi.  A Tropical Storm Watch was in effect from the border between Alabama and Mississippi to the Mouth of the Pearl River.

The circulation of Subtropical Storm Alberto remained poorly organized on Saturday.  Several low level centers dissipated and new low level centers of circulation developed on the southwestern edge of an area of thunderstorms northeast of the center.  Even though the center of circulation reorganized several times, the pressure did decrease slowly during the day.  The strongest wind speeds were occurring in the area of thunderstorms northeast of the center of circulation.  The winds were weaker south and west of the center.

Subtropical Storm Alberto will move through an environment that will become more favorable for intensification during the next 48 hours.  Alberto will move over water where the Sea Surface Temperature is near 28°C.  An upper level trough over the western Gulf of Mexico was producing southwesterly winds which were blowing across the top of the circulation.  Those winds were causing significant vertical wind shear which was inhibiting the intensification of Subtropical Storm Alberto.  The shear was also preventing thunderstorms from persisting near the center of circulation, which was keeping Alberto from making a transition to a tropical storm.  An upper level ridge was forming over Florida.  The ridge was starting to enhance upper level divergence to the east of Subtropical Storm Alberto.

The upper level trough will gradually evolve into a closed upper level low.  The vertical wind shear will slowly decrease during the next several days.  When the shear decreases, it will allow Subtropical Storm Alberto to strengthen.  Less vertical wind shear will also let thunderstorms persist closer to the center of circulation.  If thunderstorms persist near the center, then Alberto could exhibit the structure of a tropical cyclone and it could be designated as a tropical storm.  Subtropical Storm Alberto could intensify into a hurricane over the northern Gulf of Mexico.

The reformations of the low level center of circulation increase the uncertainty of track forecasts.  The upper level trough is likely to steer Subtropical Storm Alberto toward the north on Sunday.  Alberto could turn more toward the north-northwest when the trough changes into an upper level low.  On its anticipated track Subtropical Storm Alberto could approach the coast of the northern Gulf of Mexico within 48 hours.  Alberto could be a strong tropical storm or a hurricane at that time.

Subtropical Storm Alberto will be capable of causing minor wind damage when it makes landfall.  Alberto will drop locally heavy rain north and east of the center of circulation.  Flood Watches have been issued for several states in the southeastern U.S.  The Gulf Coast is very susceptible to storm surge.  There will be increases in the water level along the eastern and northern Gulf Coast where the winds blow water toward the shore.

Subtropical Storm Alberto Forms Over Northwest Caribbean Sea

Subtropical Storm Alberto formed over the northwestern Caribbean Sea on Friday morning.  The National Hurricane Center (NHC) designated an area of low pressure as Subtropical Storm Alberto on Friday morning based on data from buoys and ship reports.  At 5:00 p.m. EDT on Friday the center of Subtropical Storm Alberto was located at latitude 19.4°N and longitude 86.3°W which put it about 85 miles (135 km) south-southeast of Cozumel, Mexico.  Alberto was moving toward the east at 2 m.p.h. (3 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 1005 mb.

A Tropical Storm Watch has been issued for the portion of the U.S. coast from Indian Pass, Florida to Grand Isle, Louisiana including New Orleans.  The government of Mexico issued a Tropical Storm Watch for the portion of the coast from Tulum to Cabo Catoche.  The government of Cuba issued a Tropical Storm Watch for the province of Pinar del Rio.

The circulation around Subtropical Storm Alberto was asymmetrical.  The low level center of circulation was located just to east of the Yucatan Peninsula.  The strongest thunderstorms were occurring in a band located about 100 miles (160 km) east and north of the center.  Flow around an upper level trough over the Gulf of Mexico was producing westerly winds which were blowing toward the top of the circulation.  Those winds were causing strong vertical wind shear which was the reason why the thunderstorms were occurring well to the east of the center of circulation.

Subtropical Storm Alberto will move through an environment marginally favorable for intensification during the next 24 to 36 hours.  Alberto will move over water where  the Sea Surface Temperature is near 28°C.  So, there is sufficient energy in the upper ocean to support intensification.  However, the upper level trough will continue to cause moderate to strong vertical wind shear during the next day or so.  The wind shear will inhibit intensification.  Some gradual strengthening is possible.  The winds are weaker near the axis of the upper level trough.  If Alberto moves under the axis of the trough when it reaches the northern Gulf of Mexico, then the wind shear will decrease.  Alberto could strengthen more quickly if that happens.  There is a chance that Alberto could reach hurricane intensity.  If more thunderstorms form closer to the center of circulation, then NHC could change the designation of Alberto to a tropical storm.

Subtropical Storm Alberto is moving around the western end of a large high pressure system over the Atlantic Ocean.  The high is steering Alberto slowly toward the north-northeast.  A general motion toward the north is forecast during the next day or so.  When Alberto gets farther north, the upper level trough could steer it more toward the north-northwest.  There is a chance that the steering currents could weaken when Alberto nears the Gulf Coast.  Thus, there is much more uncertainty about the track forecast after that time.

The greatest risk with Subtropical Storm Alberto will be locally heavy rain and the potential for flooding.  Most of the heavy rain is likely to fall north and east of the center.  Much less rain is likely to fall from the western side of Alberto.  The coast of the Gulf of Mexico is very susceptible to storm surges.  The water level will rise along the eastern and northern coasts of the Gulf of Mexico where the winds blow the water toward the shoreline.

TD 01 Intensifies Into Rare April Tropical Storm Arlene

Tropical Depression 01 intensified into Tropical Storm Arlene on Thursday afternoon.  Tropical storms rarely form over the Atlantic Ocean in April and Arlene is only the second storm known to do so during the satellite era.  Of course, it would have been much harder to detect tropical storms like Arlene prior to the use of geostationary satellites for meteorological monitoring.  At 5:00 p.m. EDT on Thursday the center of Tropical Storm Arlene was located at latitude 37.7°N and longitude 42.0°W which put it about 815 miles (1315 km) west of the Azores.  Tropical Storm Arlene was moving toward the west-northwest at 25 m.p.h. (41 km/h).  The maximum sustained wind speed was 45 m.p.h. (75 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 936 mb.

A circular ring of showers and thunderstorms developed around the center of circulation of Subtropical Depression 01.  Additional narrow rainbands organized around the core of the circulation and the convection assumed a more circularly symmetrical shape.  In addition data from satellites indicated that a weak warm core had formed at the top of the circulation.  A more circular shape and a warm core are characteristics of a tropical cyclone and the National Hurricane Center changed the classification of Subtropical Depression 01 to Tropical Depression 01 in the 11:00 a.m. EDT advisory on Thursday.  Showers and thunderstorms continued to develop around the center of circulation and Tropical Depression 01 was upgraded to Tropical Storm Arlene in the 5:00 p.m. EDT advisory on Thursday.

Tropical Storm Arlene is in an environment that would not normally be considered favorable for a purely tropical weather system.  It is moving over water where the Sea Surface Temperature (SST) is near 19°C.  However, an upper low just to the west of Arlene contains colder air.  Colder air in the upper levels is providing sufficient instability to generate showers and thunderstorms even though the SST is relatively cool.  The cooler SST does mean that the showers and thunderstorms are not as tall as they would be if the water was warmer.  The upper low west of the system is producing southerly winds which are blowing over the top of Tropical Storm Arlene.  However, since the thunderstorms are not as tall, some of the stronger upper level winds are blowing over the top of Arlene’s circulation and the vertical wind shear is not having as much of an effect as might be expected.

The environment is marginal for further intensification, but the circulation looks fairly intact at the current time.  The cool SST is limiting the amount of energy that the tropical depression can extract from the ocean.  However, since the vertical wind shear is not having as much of a negative impact on the depression, some intensification may be possible during the next 24 hours.  Eventually, the wind shear is forecast to increase and Tropical Storm Arlene is forecast to weaken.

Tropical Storm Arlene is caught in the circulation of a large low pressure system to its west.  Arlene is forecast to make a counterclockwise loop as it moves around the circulation of the larger low pressure system.  It is possible that the larger low could absorb the circulation of Tropical Storm Arlene.

Subtropical Depression 01 Transitions to Tropical Depression 01

A low pressure system designated as Subtropical Depression 01 made a tropical transition to Tropical Depression 01 on Thursday morning.  At 11:00 a.m. EDT the center of Tropical Depression 01 was located at latitude 36.1°N and longitude 40.0°W which put it about 730 miles (1170 km) west of the Azores.  The tropical depression was moving toward the northwest at 14 m.p.h. (22 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. (75 km/h).  The minimum surface pressure was 996 mb.

A circular ring of showers and thunderstorms developed around the center of circulation of Subtropical Depression 01.  Additional narrow rainbands organized around the core of the circulation and the convection assumed a more circularly symmetrical shape.  In addition data from satellites indicated that a weak warm core had formed at the top of the circulation.  A more circular shape and a warm core are characteristics of a tropical cyclone and the National Hurricane Center changed the classification of Subtropical Depression 01 to Tropical Depression 01 in the 11:00 a.m. EDT advisory on Thursday.

Tropical Depression 01 is in an environment that would not normally be considered favorable for a purely tropical weather system.  It is moving over water where the Sea Surface Temperature (SST) is near 19°C.  However, an upper low just to the west of the depression contains colder air.  Colder air in the upper levels is providing sufficient instability to generate showers and thunderstorms even though the SST is relatively cool.  The cooler SST does mean that the showers and thunderstorms are not as tall as they would be if the water was warmer.  The upper low west of the system is producing southerly winds which are blowing over the top of the depression.  However, since the thunderstorms are not as tall, some of the stronger upper level winds are blowing over the top of the depression’s circulation and the vertical wind shear is not having as much of an effect as might be expected.

The environment is marginal for further intensification, but the circulation looks fairly intact at the current time.  The cool SST is limiting the amount of energy that the tropical depression can extract from the ocean.  However, since the vertical wind shear is not having as much of a negative impact on the depression, some intensification may be possible during the next 24 hours.  If the depression intensifies into a tropical storm, then it would be named Arlene.  Eventually, the wind shear is forecast to increase and the depression is forecast to weaken.

Tropical Depression 01 is caught in the circulation of a large low pressure system to its west.  Tropical Depression is forecast to make a slow counterclockwise loop as it moves around the circulation of the larger low pressure system.  It is possible that the larger low could absorb the circulation of Tropical Depression 01.