Monthly Archives: August 2019

Hurricane Dorian Rapidly Intensifies to Cat. 4

Hurricane Dorian rapidly intensified to Category 4 on the Saffir-Simpson Scale on Friday night and Hurricane Warnings were issued for the Northwestern Bahamas.  At 11:00 p.m. EDT on Friday the center of Hurricane Dorian was located at latitude 25.5°N and longitude 71.4°W which put it about 545 miles (880 km) east of West Palm Beach, Florida,  Dorian was moving toward the west-northwest at 10 m.p.h.  The maximum sustained wind speed was 140 m.p.h. (220 km/h) and there were wind gusts to 165 m.p.h. (270 km/h).  The minimum surface pressure was 948 mb.

Hurricane Warnings were issued for the Northwestern Bahamas including the Abacos, Berry Islands, Bimini, Eleuthera, Grand Bahama Island and New Providence.  A Hurricane Watch was in effect for Andros Island.

When reconnaissance aircraft reached the core of Hurricane Dorian on Friday night they discovered that Dorian has intensified rapidly since Friday afternoon.  The minimum surface pressure had decreased by more than 20 mb and the maximum sustained wind speed was 140 m.p.h. (220 km/h).  Dorian was a very symmetrical, if small hurricane.  There was a circular eye with a diameter to 14 miles (22 km) at the center of circulation.  The eye was surrounded by a ring of strong thunderstorms and the strongest winds were occurring in that ring of storms.  Bands of showers and thunderstorms were revolving around the core of Hurricane Dorian.  Storms around the core were generating upper level divergence which was pumping mass away from the hurricane.

The circulation around Hurricane Dorian was still relatively small.  Winds to hurricane force extended out about 25 miles (40 km) from the center of circulation.  Winds to tropical storm force extended out about 110 miles (170 km) from the center.  The Hurricane Intensity Index (HII) for Hurricane Dorian was 28.3.  The Hurricane Size Index (HSI) was 12.0 and the Hurricane Wind Intensity Size Index (HWISI) was 40.3.  Hurricane Dorian was capable of causing regional significant damage.

Hurricane Dorian will remain in an environment favorable for strong hurricanes for several more days.  Dorian will move over water where the Sea Surface Temperature is near 29°C.   It will move through a region where the upper level winds are weak and there will be little vertical wind shear.  Hurricane Dorian could intensify to Category 5 hurricane on the Saffir-Simpson Scale.  At some point a rainband will wrap around the existing eye and eyewall.  That will begin an eyewall replacement cycle that will weaken Hurricane Dorian, at least temporarily.

Hurricane Dorian will move south of a subtropical ridge of high pressure over the western Atlantic Ocean.  The high will steer Dorian toward the west during the next 48 to 72 hours.  Dorian will move much more slowly when it reaches the western end of the ridge.  On its anticipated track Hurricane Dorian could reach the Northwestern Bahamas on Sunday.  Dorian could approach the southeast coast of Florida on Tuesday.

Dorian Strengthens to Major Hurricane

Hurricane Dorian strengthened to a major hurricane on Friday afternoon.  Data from a reconnaissance plane indicated that Hurricane Dorian had strengthened to Category 3 on the Saffir-Simpson Scale on Friday afternoon, which meant it was a major hurricane.  At 2:00 p.m. EDT on Friday the center of Hurricane Dorian was located at latitude 24.8°N and longitude 70.3°W which put it about 625 miles (1005 km) east of West Palm Beach, Florida.  Dorian was moving toward the northwest at 10 m.p.h. (16 km/h).  The maximum sustained wind speed was 115 m.p.h. (185 km/h) and there were wind gusts to 140 m.p.h. (225 km/h).  The minimum surface pressure was 970 mb.

Hurricane Watches had been issued for the Northwestern Bahamas.

The circulation around Hurricane Dorian exhibited much more impressive organization on satellite images and radar products generated by reconnaissance aircraft.  Clouds cleared out of the eye and it became even more circular.  The diameter of the eye was 21 miles (34 km).  The eye was surround by a ring of strong thunderstorms and the strongest winds were occurring in that ring of storms.  The overall appearance of Hurricane Dorian was more symmetrical.  Bands of showers and thunderstorms were revolving around the core of the circulation.  Storms around the core generating upper level divergence which was pumping mass away from the hurricane.

The circulation around Hurricane Dorian was still small.  Winds to hurricane force extended out about 25 miles from the center of circulation.  Winds to tropical storm force extended out about 100 miles from the center.  The Hurricane Intensity Index (HII) for Dorian was 20.6.  The Hurricane Size Index (HSI) was 9.0 and the Hurricane Wind Intensity Index (HWISI) was 29.6.  Hurricane Dorian was already capable of causing major damage.

Hurricane Dorian will move through an environment that is favorable for intensification.  Dorian will move over water where the Sea Surface Temperature is near 29°C.  It will move through a region where the upper level winds are weak and there will be little vertical wind shear.  Hurricane Dorian could start a period of rapid intensification at any time.  Dorian will almost certainly intensify to Category 4 and there is the potential for it to strengthen to Category 5.  After Hurricane Dorian strengthens, eyewall replacement cycles could cause fluctuations in intensity.

A ridge of high pressure north of Hurricane Dorian is starting to turn Dorian more toward the west.  The high is forecast to steer Dorian toward the west during the next two to three days.  On its anticipated track Hurricane Dorian will be near the Northwestern Bahamas on Sunday and it will approach the southeast coast of Florida on Monday.  Dorian will reach the western end of the high when it gets close to the Florida coast.  Hurricane Dorian could slow down and turn northward on Tuesday.

Hurricane Dorian Strengthens East of the Bahamas

Hurricane Dorian resumed strengthening east of the Bahamas on Thursday night after exhibiting little change of intensity during much of the day.  At 11:00 p.m. EDT on Thursday the center of Hurricane Dorian was located at latitude 23.3°N and longitude 68.4°W which put it about 580 miles (930 km) east of the Northwestern Bahamas.  Dorian was moving toward the northwest at 12 m.p.h. (19 km/h).  The maximum sustained wind speed was 105 m.p.h. (165 km/h) and there were wind gusts to 125 m.p.h. (200 km/h).  The minimum surface pressure was 977 mb.

The structure of Hurricane Dorian exhibited little change for much of Thursday.  Storms around the core of Dorian grew stronger on Thursday evening.  An eye with a diameter of 10 miles (16 km) developed at the center of circulation.  A nearly complete ring of thunderstorms surrounded the eye and the strongest winds were occurring in that ring of storms.  Bands of showers and thunderstorms were revolving around the core of Hurricane Dorian.  Storms near the core were generating upper level divergence which was pumping mass away from the hurricane.  The removal of mass allowed the surface pressure to start decreasing again.  The circulation around Dorian was still relatively small.  Winds to hurricane force extended out about 25 miles (40 km) from the center of circulation.  Winds to tropical storm force extended out about 100 miles (160 km) from the center.

Hurricane Dorian will move through an environment favorable for intensification during the next 24 to 48 hours.  Dorian will move over water where the Sea Surface Temperature is near 29°C.  It will move through a region where the upper level winds are weak and there will be little vertical wind shear.  Hurricane Dorian is likely to intensify to major hurricane status on Friday.  There is the potential for Dorian to strengthen to Category 5 on the Saffir-Simpson Scale during the weekend.  When Hurricane Dorian becomes a major hurricane, eyewall replacement cycles could cause fluctuations in its intensity.

A ridge of high pressure will build north of Hurricane Dorian on Friday.  The high will block Dorian from moving toward the north and it will turn the hurricane toward the west.  On its anticipated track Hurricane Dorian could approach the Northwestern Bahamas on Sunday and the east coast of Florida on Monday.  Dorian is likely to be a small, but very dangerous hurricane.

Tropical Storm Podul Drops Heavy Rain on Vietnam

Tropical Storm Podul dropped heavy rain on Vietnam on Thursday.  At 2:00 p.m. EDT on Thursday the center of Tropical Storm Podul was located at latitude 17.5°N and longitude 106.5°E which put it about 10 miles (15 km) northwest of Dong Hoi, Vietnam.  Podul was moving toward the west at 21 m.p.h. (34 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.

Tropical Storm Podul made landfall near Dong Hoi, Vietnam on Thursday.  The structure of Podul was very asymmetrical.  Most of the thunderstorms were occurring in the western half of the circulation.  Tropical Storm Podul was moving south of an upper level ridge over eastern Asia.  The ridge was producing strong easterly winds which were blowing across the top of Podul.  Those winds were causing strong vertical wind shear and they were the reason why most of the thunderstorms were in the western half of the circulation.  As a result of the wind shear, heavy rain was already falling over Vietnam even before the center made landfall.

The upper level ridge was steering Tropical Storm Podul rapidly toward the west.  Podul will weaken quickly as it moves farther inland.  Even though Tropical Storm Podul will weaken quickly, heavy rain will fall over portions of Laos and northeastern Thailand on Friday.  Locally heavy rainfall could cause flash floods in parts of Vietnam, Laos and northeastern Thailand.

Hurricane Dorian Strengthens North of Puerto Rico

Hurricane Dorian strengthened north of Puerto Rico on Wednesday.  At 11:00 p.m. EDT on Wednesday the center of Hurricane Dorian was located at latitude 19.7°N and longitude 66.0°W which put it about 90 miles (145 km) north of San Juan, Puerto Rico.  Dorian was moving toward the northwest at 13 m.p.h. (20 km/h).  The maximum sustained wind speed was 85 m.p.h. (135 km/h) and there were wind gusts to 110 m.p.h. (170 km/h).  The minimum surface pressure was 986 mb.

The circulation around Hurricane Dorian strengthened steadily on Wednesday.  A circular eye with a diameter of 14 miles (22 km) formed at the center of circulation.  A closed ring of thunderstorms surrounded the eye and the strongest winds were occurring in the northeastern part of that ring.  Bands of showers and thunderstorms were revolving around the core of Hurricane Dorian.  Storms near the core were generating upper level divergence which was pumping mass away to the north and northeast of the hurricane.  The circulation around Hurricane Dorian remained fairly small.  Winds to hurricane force extended out about 20 miles (30 km) in the northeastern quadrant of Dorian.  Winds to tropical storm force extended out about 70 miles from the center of circulation.

Hurricane Dorian will move through an environment favorable for intensification during the next several days.  Dorian will move over water where the Sea Surface Temperature is near 29°C.  It will move into an area where the upper level winds are relatively weak and there will be little vertical wind shear.  Hurricane Dorian is very likely to intensify during the next 48 hours and it could intensify rapidly at times.  Dorian is likely to strengthen into a major hurricane.

An upper level low near the Bahamas will pull Hurricane Dorian toward the northwest during the next 24 to 36 hours.  A strong ridge of high pressure will build north of Dorian on Friday.  The high will block Dorian from moving north and it will turn it toward the west-northwest.  On its anticipated track Hurricane Dorian could be near the northern Bahamas on Saturday night.  Dorian could approach the east coast of Florida by later on Sunday.  Dorian is likely to be a major hurricane when it approaches Florida.

Tropical Storm Dorian Strengthens, Hurricane Warnings for Virgin Islands

Tropical Storm Dorian strengthened on Wednesday morning and it was on the verge of becoming a hurricane.  Hurricane Warnings were issued for Vieques, Culebra, the U.S. Virgin Islands and the British Virgin Islands. At 11:00 a.m. EDT on Wednesday the center of Tropical Storm Dorian was located at latitude 17.5°N and longitude 64.5°W which put it about 25 miles (40 km) south of St. Croix.  The maximum sustained wind speed was 70 m.p.h. (110 km/h) and there were wind gusts to 90 m.p.h. (145 km/h).  The minimum surface pressure was 999 mb.

Hurricane Warnings were in effect for Vieques, Culebra, the U.S. Virgin Islands, and the British Virgin Islands.  A Tropical Storm Warning and a Hurricane Watch was in effect for Puerto Rico.  A Tropical Storm Watch was in effect for the portion of the coast of the Dominican Republic from Isla Saona to Samana.

The circulation around Tropical Storm Dorian exhibited much greater organization on Wednesday morning.  A ring of strong thunderstorms wrapped almost completely around the center of circulation.  The strongest winds were occurring in the northeastern part of that ring of storms.  Bands of showers and thunderstorms were revolving around the core of Dorian.  Storms near near the core were generating upper level divergence which was pumping mass away to the north and northeast of the tropical storm.  The circulation also increased in size on Wednesday morning.  Winds to tropical storm force extended out about 70 miles (110 km) from the center of circulation.

Tropical Storm Dorian will move through an environment favorable for intensification during the next few days.  Dorian will move over water where the Sea Surface Temperature is near 29°C.  It will move northeast of an upper level low during the next 24 hours.  The low will produce some southerly winds which will blow toward the top of the circulation, but the winds will not be strong enough to prevent intensification.  The wind shear will decrease on Friday and Dorian could strengthen into a major hurricane near the Bahamas.

The upper level low will help to steer Tropical Storm Dorian toward the northwest during the next 24 to 36 hours.  A ridge of high pressure will build north of Dorian on Friday.  The ridge will block Dorian from moving north and it will steer Dorian toward the west-northwest.  On its anticipated track Tropical Storm Dorian will pass over the Virgin Islands near the eastern end of Puerto Rico today.  Dorian will be near the northern Bahamas on Saturday and it could approach the east coast of Florida by Sunday night.  Dorian could be a major hurricane when it approaches the east coast of the U.S.

Elsewhere over the Atlantic Ocean, former Tropical Storm Erin weakened to a tropical depression.  At 11:00 a.m. EDT on Wednesday the center of Tropical Depression Erin was located at latitude 33.6°N and longitude 72.8°W which put it about 190 miles (305 km) southeast of Cape Hatteras, North Carolina.  Erin was moving toward the 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. (75 km/h).  The minimum surface pressure was 1006 mb.

Tropical Storm Dorian Moves Toward Puerto Rico

Tropical Storm Dorian moved toward Puerto Rico on Tuesday.  At 11:00 p.m. EDT on Tuesday the center of Tropical Storm Dorian was located at latitude 16.0°N and longitude 63.0°W which put it about 275 miles (440 km) east-southeast of Ponce, Puerto Rico.  Dorian was moving toward the northwest at 13 m.p.h. (20 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 1006 mb.

A Hurricane Watch was issued for Puerto Rico.  Tropical Storm Warnings were in effect for Puerto Rico, Culebra, Vieques, the U.S. Virgin Islands and the British Virgin Islands.  A Tropical Storm Watch was issued for the coast of the Dominican Republic from Isla Saona to Puerto Plata.

The original low level center of Tropical Storm Dorian passed south of Barbados and St. Lucia on Tuesday morning.  Dorian dropped heavy rain and there were reports of flash floods on Martinique.  The original center weakened on Tuesday afternoon and a new low level center formed about 60 miles farther to the north.  The formation of a new center of circulation caused the forecast future track of Tropical Storm Dorian to be shifted northward as well.

Even with the formation of a new center of circulation, the overall circulation around Tropical Storm Dorian did not change much on Tuesday.  The circulation around Dorian remained small.  Winds to tropical storm force only extended out about 45 miles (75 km) from the center of circulation.  A broken ring of thunderstorms surrounded the new low level center.  Bands of showers and thunderstorms were revolving the center of Tropical Storm Dorian.  Storms near the center were producing upper level divergence which was pumping mass away to the north of the tropical storm.

Tropical Storm Dorian will move through an environment somewhat favorable for intensification on Wednesday.  Dorian will move over water where the Sea Surface Temperature is near 29°C.  An upper level low northwest of Puerto Rico will produce southerly winds which will blow toward the top of the circulation.  Those winds will cause some vertical wind shear, which will inhibit intensification.  A large mass of drier air is north of Tropical Storm Dorian and the drier air could also inhibit intensification if it gets pulled into the circulation around Dorian.  The small size of the circulation around Tropical Storm Dorian means that it could weaken or strengthen quickly if the environmental conditions change significantly.  Dorian is likely to weaken when it crosses Puerto Rico on Wednesday night.

The upper low northwest of Puerto Rico will help to steer Tropical Storm Dorian toward the northwest on Wednesday.  On its anticipated track Tropical Storm Dorian could reach Puerto Rico by Wednesday evening.  Dorian will bring gusty winds and it will drop locally heavy rain on Puerto Rico.  Locally heavy rain could cause flash floods in some locations.  A high pressure system will build north of Tropical Storm Dorian on Thursday and Friday.  The high will turn Dorian back toward the west-northwest.  Dorian could approach the east coast of Florida on Sunday.

Elsewhere over the Atlantic Ocean, Tropical Depression Six strengthened into Tropical Storm Erin southeast of Cape Hatteras on Tuesday night.  At 11:00 p.m. EDT on Tuesday the center of Tropical Storm Erin was located at latitude 31.9°N and longitude 72.1°W which put it about 300 miles (485 km) southeast of Cape Hatteras, North Carolina.  Erin was moving toward the west 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. (65 km/h).  The minimum surface pressure was 1005 mb.  Tropical Storm Erin is forecast to move northeast toward Nova Scotia.

Tropical Storm Dorian Brings Wind and Rain to Barbados

Tropical Storm Dorian brought wind and rain to Barbados on Monday night.  Observations made by a U.S. Air Force Reserve Hurricane Hunter aircraft indicated that the center of Tropical Storm Dorian passed just south of Barbados on Monday night.  Dorian brought winds to tropical storm force and locally heavy rain.  At 11:00 p.m. EDT on Monday the center of Tropical Storm Dorian was located at latitude 13.2°N and longitude 59.7°W which put it about 95 miles (155 km) east-southeast of St. Lucia.  Dorian was moving toward the west-northwest at 13 m.p.h. (20 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 1003 mb.

Tropical Storm Warnings were in effect for Barbados, St. Lucia, Martinique, St. Vincent and the Grenadines. Tropical Storm Watches have been issued for Puerto Rico, Grenada, Dominica, Saba and St. Eustatius.

The circulation around Tropical Storm Dorian remained fairly small on Monday.  Winds to tropical storm force only extended out about 45 miles (75 km) from the center of circulation.  Thunderstorms were occurring primarily in bands in the northern half of the circulation.  Bands in the southern half of the circulation consisted primarily of showers and lower clouds.  Storms near the center of Dorian were generating upper level divergence which was pumping mass away from the tropical storm.

Tropical Storm Dorian will move through an environment somewhat favorable for intensification.  Dorian will move over water where the Sea Surface Temperature is near 29°C.  Tropical Storm Dorian will move south of an upper level ridge.  The ridge will produce easterly winds which will cause some vertical wind shear, but the shear should not be strong enough to prevent intensification.  Dorian will move just south of a large mass of drier air.  It appears that some drier air will get pulled into circulation at times and the drier air will interrupt periods of intensification.  Since the circulation around Tropical Storm Dorian is very small, Dorian could strengthen or weaken very quickly if environmental conditions change.

Tropical Storm Dorian will move south of a subtropical high pressure system over the Atlantic Ocean.  The high will steer Dorian toward the west-northwest during the next several days.  On its anticipated track the center of Tropical Storm Dorian will pass near St. Lucia on Tuesday morning.  Dorian could approach Puerto Rico on Wednesday.

Elsewhere over the Atlantic Ocean, Tropical Depression Six formed off the southeast coast of the U.S.  At 11:00 p.m. EDT on Monday the center of Tropical Depression Six was located at latitude 31.5N and longitude 72.2W which put it about 320 miles southeast of Cape Hatteras, North Carolina. It was moving toward the east at 3 m.p.h. The maximum sustained wind speed was 35 m.p.h. and the minimum surface pressure was 1010 mb.

Tropical Storm Podul Forms East of Luzon

Tropical Storm Podul formed east of Luzon on Monday night.  At 11:00 p.m. EDT on Monday the center of Tropical Storm Podul was located at latitude 15.1°N and longitude 125.2°E which put it about 250 miles (400 km) east of Baler, Philippines.  Podul was moving a little to the north of due west at 25 m.p.h. (40 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 998 mb.

A low level center of circulation in an area of thunderstorms east of Luzon was visible in satellite imagery on Monday night and the Japan Meteorological Agency designated the system as Tropical Storm Podul.  The circulation around Tropical Storm Podul was not well organized.  Many of the thunderstorms were occurring in broken bands west of the center of circulation.  Bands in the eastern half of Podul consisted primarily showers and lower clouds.  Tropical Storm Podul was moving south of an upper level ridge over eastern Asia and the Western North Pacific Ocean.  The ridge was producing easterly winds which were causing moderate vertical wind shear.  The shear was contributing to the poorly organized circulation around Podul.

Tropical Storm Podul will move through an environment mostly unfavorable for intensification during the next 24 hours,  Podul will move over water where the Sea Surface Temperature is near 29°C.  However, the upper level ridge will continue to cause moderate vertical wind shear.  The center will move across northern Luzon and increased friction will weaken the circulation.  Tropical Storm Podul could weaken to a tropical depression when it crosses Luzon.  Podul could strengthen in the middle of the week when it moves west of Luzon and out over the South China Sea.

Tropical Storm Podul will move south of a subtropical ridge over the Western North Pacific Ocean.  The ridge will steer Podul a little to the north of due west during the next few days.  On its anticipated track Tropical Storm Podul will move across northern Luzon on Tuesday. Podul will cause gusty winds and locally heavy rain.  The rain could cause flash floods in some locations.  Tropical Storm Podul will move west of Luzon and over the South China Sea in about 24 hours.  Podul could approach Hainan Island in about 72 hours.

Stronger Tropical Storm Dorian Causes Warnings for Lesser Antilles

Tropical Storm Dorian strengthened on Sunday and the threat it posed caused warnings and watches to be issued for some of the Lesser Antilles.  Tropical Storm Warnings were in effect for Barbados, St. Lucia, and St. Vincent and the Grenadines.  Tropical Storm Watches were issued for Grenada and Martinique.

At 5:00 p.m. EDT on Sunday the center of Tropical Storm Dorian was located at latitude 11.5°N and longitude 54.2°W which put it about 375 miles (605 km) east-southeast of Barbados.  Dorian was moving a little to the north of due west at 14 m.p.h. (22 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 1003 mb.

The circulation around Tropical Storm Dorian exhibited greater organization on Sunday afternoon.  The inner end of a band of showers and thunderstorms wrapped tightly around the northern and western sides of the center of circulation.  The strongest winds were occurring in that band.  Several other bands of showers and storms were revolving around the small core of Dorian.  Storms near the center of circulation were generating upper level divergence which was pumping mass away to the north of the tropical storm.  The circulation around Tropical Storm Dorian was small.  Winds to tropical storm force extended out about 35 miles (55 km) from the center of circulation.

Tropical Storm Dorian will move through an environment mostly favorable for intensification.  Dorian will move over water where the Sea Surface Temperature is near 28.5°C.  It will move through a region where the upper level winds are relatively weak and there will be little vertical wind shear.  A large area of drier air is north of Tropical Storm Dorian.  If the circulation draws drier air into the tropical storm, it would interrupt intensification.  Tropical Storm Dorian is likely to strengthen during the next 24 to 48 hours.  Since Dorian has a small circulation, it could intensify or weaken quickly if the environmental conditions change.

Tropical Storm Dorian will move south of the subtropical high pressure system over the North Atlantic Ocean.  The high will steer Dorian toward the west-northwest during the next few days.  On its anticipated track Tropical Storm Dorian could approach Barbados late on Monday.  It could be a hurricane by that time.  Dorian could reach the southern and central Lesser Antilles on Tuesday.  Tropical Storm Dorian could bring strong winds and heavy rain to those islands.