Tag Archives: AL11

Hurricane Irma Strengthens to Cat. 4, Watch in effect for Puerto Rico

Hurricane Irma strengthened to Category 4 on the Saffir-Simpson Scale on Monday and a Hurricane Watch was issued for Puerto Rico and the U.S. Virgin Islands.  At 5:00 p.m. EDT on Monday the center of Hurricane Irma was located at latitude 16.7°N and longitude 54.4°W which put it about 490 miles (790 km) east of the Leeward Islands.  Irma was moving toward the west at 13 m.p.h. (20 km/h).  The maximum sustained wind speed was 130 m.p.h. (215 km/h) and there were wind gusts to 160 m.p.h. (260 km/h).  The minimum surface pressure was 944 mb.

Hurricane Warnings are in effect for Antigua, Barbuda, Anguilla, Montserrat, St. Kitts, Nevis, Saba, St. Eustatius, St. Maarten, St. Martin, and St. Barthelemy.  Hurricane Watches are in effect for Guadeloupe, the British Virgin Islands, the U.S. Virgin Islands, Puerto Rico, Vieques and Culebra.  A Tropical Storm Warning is in effect for Guadeloupe.  A Tropical Storm Watch is in effect for Dominica.

The circulation of Hurricane Irma has been going through a series of eyewall replacement cycles.  A plane flying through Irma reported concentric eyewalls earlier today.  The two eyewalls appear to have merged.  A small circular eye is at the center of circulation.  A ring of strong thunderstorms surrounds the eye and the strongest winds are occurring in that ring of storms.  Additional bands of showers and thunderstorms are revolving around the core of Hurricane Irma.  Storms around the center are generating strong upper level divergence which is pumping away mass in all directions from the hurricane.

Hurricane Irma has been increasing in size.  Winds to hurricane force extend out about 40 miles (65 km) from the center of circulation.  Winds to tropical storm force extend out about 140 miles (225 km) from the center.  The Hurricane Intensity Index (HII) for Hurricane Irma is 25.1.  The Hurricane Size Index (HSI) is 13.6.  The Hurricane Wind Intensity Size index (HWISI) is 38.7.

Hurricane Irma will move through an environment very favorable for tropical cyclones.  Irma will move over water where the Sea Surface Temperature is near 30°C.  The upper level winds are weak and there is little vertical wind shear.  Hurricane Irma could strengthen further and it has a chance to reach Category 5 on the Saffir-Simpson Scale.  Hurricane Irma is likely to go through additional eyewall replacement cycles, which will cause fluctuations in its intensity, but Irma should remain a strong hurricane as it nears the northern Leeward Islands.

The subtropical high pressure system over the Atlantic Ocean has been steering Hurricane Irma toward the west and that general motion is expected to continue for another 12 to 24 hours.  After that time Irma is expected to turn more toward the west-northwest.  On its anticipated track Hurricane Irma will approach the northern Leeward Islands late on Tuesday.  Hurricane Irma could approach Puerto Rico on Wednesday.

Hurricane Irma Moves Toward Leeward Islands, Watches Issued

Hurricane Irma moved toward the northern Leeward Islands on Sunday and Hurricane Watches were issued for a number of those islands.  At 11:00 p.m. EDT on Sunday the center of Hurricane Irma was located at latitude 17.2°N and longitude 51.0°W which put it about 710 miles (1145 km) east of the Leeward Islands.  Irma was moving toward the west-southwest at 14 m.p.h. (22 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 961 mb.

Hurricane Watches were in effect for Antigua, Barbuda, Anguilla, Montserrat, St. Kitts, Nevis, Saba, St. Eustatius, St. Maarten, St, Martin, and St. Barthelemy.

The circulation of Hurricane Irma is very well organized.  There is a nearly circular eye with a diameter of 30 miles (48 km) at the center of circulation.  The eye is surrounded by a ring of strong thunderstorms and the strongest winds are occurring in the northeastern part of the ring.  Bands of showers and thunderstorms are revolving around the core of Hurricane Irma.  Thunderstorms around the core are generating strong upper level divergence which is pumping mass away in all directions from the hurricane.  Winds to hurricane force extend out about 35 miles (55 km) from the center.  Winds to tropical storm force extend out about 140 miles (225 km) from the center.

The Hurricane Intensity Index (HII) for Hurricane Irma is 20.6.  The Hurricane Size Index (HSI) is 11.7 and the Hurricane Wind Intensity Size Index (HWISI) is 32.3.

Hurricane Irma will move through an environment favorable for intensification.  Irma will move over water where the Sea Surface Temperature is near 29°C and there is warmer water farther west.  The upper level winds are weak and there is little vertical wind shear.  Hurricane Irma could intensify into a Category 4 hurricane on the Saffir-Simpson Scale.  There is a possibility that Irma could strengthen to Category 5 when it passes near the northern Leeward Islands and moves toward the Bahamas.  Hurricane Irma has already completed several eyewall replacement cycles and there could be more.  Each eyewall replacement cycle could result in fluctuations in the intensity of Hurricane Irma.

A strong subtropical high pressure system over the Atlantic Ocean is steering Hurricane Irma toward the west-southwest.  The high is forecast to weaken just a bit during the next several days and Hurricane Irma is expected to move more toward the west-northwest.  On its anticipated track Hurricane Irma will approach the northward Leeward Islands on Tuesday night.  It will be a strong, dangerous hurricane at that time.

Hurricane Irma Completes Quick Eyewall Replacement Cycle and Strengthens

Hurricane Irma completed a quick eyewall replacement cycle on Friday and it strengthened after the cycle ended.  At 5:00 p.m. EDT on Friday the center of Hurricane Irma was located at latitude 18.8°N and longitude 39.1°W which put it about 1495 miles (2405 km) east of the Leeward Islands.  Irma was moving toward the west at 13 m.p.h. (20 km/h).  The maximum sustained wind speed was 120 m.p.h. (195 km/h) and there were wind gusts to 150 m.p.h. (240 km/h).  The minimum surface pressure was 964 mb.

Hurricane Irma is a small circular hurricane.  There is a small eye at the center of circulation. The eye is surrounded by a ring of strong thunderstorms.  Additional bands of showers and thunderstorms are revolving around the eye.  Winds to hurricane force only extend out about 25 miles (40 km) from the center of circulation.  Winds to tropical storm force only extend out about 100 miles (160 km) from the center.  The thunderstorms around the center are generating well developed upper level divergence which is pumping mass away in all directions.

The Hurricane Intensity Index (HII) for Irma is 22.1  The Hurricane Size Index (HSI) is 7.6 and the Hurricane Wind Intensity Size Index (HWISI) is 29.7.

Hurricane Irma will move through an environment favorable for intensification.  Irma will move over water where the Sea Surface Temperature is near 28°C.  The upper level winds are weak and there is little vertical wind shear.  Hurricane Irma is likely to intensify further, but there are also likely to be additional eyewall replacement cycles which will cause fluctuations in the intensity.

Hurricane Irma is located south of the subtropical high over the Atlantic Ocean.  The high is steering Irma toward the west.  The high is forecast to strengthen over the weekend and it is likely to steer Hurricane Irma more toward the west-southwest.  On its anticipated track Hurricane Irma could approach the Leeward Islands early next week.

Hurricane Irma Strengthens Rapidly Over Atlantic

Hurricane Irma strengthened rapidly as it moved over the tropical Atlantic Ocean.  At 11:00 a.m. EDT on Thursday the center of Hurricane Irma was located at latitude 16.9°N and longitude 33.8°W which put it about 1845 miles (2975 km) east of the Leeward Islands.  Irma was moving toward the west-northwest at 10 m.p.h. (16 km/h).  The maximum sustained wind speed was 100 m.p.h. (160 km/h) and there were wind gusts to 120 m.p.h. (195 km/h).  The minimum surface pressure was 979 mb.

Hurricane Irma intensified rapidly on Thursday morning.  A circular eye developed at the center of circulation and a ring of strong thunderstorms surrounded the eye.  Numerous bands of showers and thunderstorms developed outside the core of Irma.  Hurricane Irma has a very circular, symmetrical shape.  Thunderstorms in the core of Irma were generating strong upper level divergence which was pumping mass away in all directions from the hurricane.

Hurricane Irma will move through an environment favorable for intensification during the next few days.  Irma will move over water where the Sea Surface Temperature is near 28°C.  Irma is under the western end of an upper level ridge, but the upper level winds are weak and there is not much vertical wind shear.  Irma is likely to intensify during the next few days and it is forecast to become a major hurricane.  Hurricanes that intensify rapidly often develop concentric eyewalls, which cause fluctuations in their intensity.  It is highly likely that Hurricane Irma will go through one of more eyewall replacement cycles which will cause temporary fluctuations in the wind speed.  Eyewall replacement cycles often result in a larger hurricane and Hurricane Irma has the potential to develop into a big classic Cape Verde hurricane.

Hurricane Irma is nearing a weaker region in the subtropical ridge to its north.  The weakness is allowing Irma to move toward the west-northwest.  The ridge is expected to strengthen and steer Hurricane Irma more toward the west or west-southwest during the next few days.  On its anticipated track Hurricane Irma is forecast to be a major hurricane east of the Leeward Islands in five days.  The uncertainty about the future track of Hurricane Irma increases after that time.  People around the western Atlantic need to monitor the progress of Hurricane Irma.

Tropical Storm Harvey Moves Into Louisiana, Irma Strengthens Quickly

Tropical Storm Harvey finally moved into Louisiana on Wednesday after lingering for several days over the northwestern Gulf of Mexico.  Harvey weakened to a tropical depression after it moved inland.  At the same time a new tropical storm named Irma strengthened quickly over the eastern Atlantic Ocean.  At 11:00 p.m. EDT on Wednesday the center of Tropical Depression Harvey was located at latitude 31.7°N and longitude 92.3°W which put it about 30 miles (50 km) north-northeast of Alexandria, Louisiana.  Harvey was moving toward the north-northeast 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. (75 km/h).  The minimum surface pressure was 998 mb.

After dropping record rainfall and causing destructive floods of parts of southeastern Texas and western Louisiana, Tropical Depression Harvey finally started to move steadily toward the north-northeast on Wednesday.  Harvey was still producing heavy rain over parts of western Louisiana, but the fact that it was moving should limit the total rainfall at any location.  Bands of showers and thunderstorms on the far eastern periphery of Harvey’s circulation were also dropping heavy rain.  Some of those thunderstorms were strong enough to approach severe criteria.  Tropical Depression Harvey is forecast to move toward the Ohio River Valley during the next several days and it will bring windy, wet weather to the Middle Mississippi and Ohio River Valleys.  Rain associated with the circulation of Tropical Depression Harvey could also reach the Mid-Atlantic States later this week.

At 11:00 p.m. EDT on Wednesday the center of Tropical Storm Irma was located at latitude 16.4°N and longitude 32.2°W which put it about 545 miles (875 km) west of the Cabo Verde Islands.  Irma was moving toward the west at 12 m.p.h. (19 km/h).  The maximum sustained wind speed was 65 m.p.h. (105 km/h) and there were wind gusts to 80 m.p.h. (130 km/h).  The minimum surface pressure was 999 mb.

The circulation of Tropical Storm Irma organized quickly on Wednesday.  Numerous bands of showers and thunderstorms formed and began to revolve around a well organized center of circulation.  Thunderstorms in the core of Irma generated well developed upper level divergence which pumped away mass in all direction.  There were occasional satellite images which hinted that an eye could be forming at the center of Tropical Storm Irma.

Tropical Storm Irma will be moving through an environment that will be favorable for intensification.  Irma will move over water where the Sea Surface Temperature is near 28°C.  The upper level winds are weak and there is little vertical wind shear.  Irma is likely to become a hurricane on Thursday and it could intensify rapidly if an eye forms.  Tropical Storm Irma is forecast to become a major hurricane and it could become one of the big classic Cape Verde hurricanes.

A strong subtropical high to the north of Irma is steering the tropical storm toward the west and a general westerly motion is forecast to continue for the next few days.  There is more divergence in the model guidance after a few days and the future track of Irma when it nears the Lesser Antilles is more uncertain.  Tropical Storm Irma has the potential to become a big dangerous hurricane and it will need to be watched carefully.

Tropical Storm Julia Edges Farther from the Southeast U.S.

Tropical Storm Julia moved slowly eastward on Thursday which took it farther from the Southeastern coast of the U.S.  At 5:00 p.m. EDT on Thursday the center of Tropical Storm Julia was located at latitude 32.1°N and longitude 77.1°W which put it about 150 miles (245 km) south-southeast of Wilmington, North Carolina.  Julia was moving toward the east at 8 m.p.h. (13 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 1007 mb.

The circulation of Tropical Storm Julia is not well organized.  All of the stronger thunderstorms are well to the east of the center of circulation.  The broad low level circulation is elongated from the west-southwest of the east-northeast.  There are no thunderstorms close to the center of circulation.

Tropical Storm Julia is in an environment that is unfavorable for intensification.  It is moving over water where the Sea Surface Temperature is near 29°C.  So, there is sufficient energy in the upper ocean to support intensification.  However, upper level westerly winds are causing strong vertical wind shear.  The upper level winds have at least temporarily blown the upper part of the circulation east of the lower third of the circulation.  As long as the upper level winds are as strong as they are now, Tropical Storm Julia will slowly weaken.  If the upper level winds slow down, then more thunderstorms could develop near the center and Julia could get a little stronger.  With the current strong vertical wind shear Tropical Storm Julia should slowly weaken during the next few hours.

The vertical structure of Tropical Storm Julia maintained enough integrity that the westerly winds pushed the thunderstorms toward the east and they dragged the low level center with them.  However, it now appears that the vertical parts of the circulation have separated.  The low level circulation is being steered slowly back toward the southwest by a surface high pressure system to the north of Julia.  Tropical Storm Julia could move erratically during the next several days.  As long as no thunderstorms form near the center, it will drift slowly toward the southwest.  Any time thunderstorms form near the center of circulation, the taller storm will be pushed toward the east.

Tropical Storm Julia Forms over Northeast Florida

Although tropical storms normally form over an ocean, Tropical Storm Julia formed over northeast Florida on Tuesday.  The National Hurricane Center (NHC) had tracked a tropical disturbance from Africa across the Atlantic Ocean to Florida.  NHC had designated the system as Invest 93L for tracking purposes.  Although the disturbance moved over the Florida peninsula on Monday, a distinct center of circulation developed at the surface on Tuesday while the disturbance moved north over the northeastern part of Florida.  An area of stronger thunderstorms formed over the Atlantic Ocean east of the center of circulation on Tuesday afternoon and persisted into Tuesday evening.  Because the system had a distinct surface center, persistent thunderstorms and winds to tropical storm force, the National Hurricane Center named it Tropical Storm Julia at 11:00 p.m. EDT on Tuesday and initiated advisories on the Julia.

At 11:00 p.m. EDT on Tuesday the center of Tropical Storm Julia was located at latitude 30.3°N and longitude 81.6°W which put it about 5 miles (10 km) west of Jacksonville, Florida.  Julia was moving toward the north-northwest 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 1009 mb.

A Tropical Storm Warning has been issued for the portion of the coast from Ponte Vedra Beach, Florida to Altamaha Sound, Georgia.

The circulation of Tropical Storm Julia is very asymmetrical.  Most of the thunderstorms and rain are north and east of the of circulation.  There are few storms or rain west and south of the center.  One primary rainband extends part of the way around the southeastern portion of the circulation.  The thunderstorms to the east of the center are generating upper level divergence which is pumping out mass to the northeast of the circulation.

Since the center of Tropical Storm Julia is over land, intensification would normally be unlikely.  However, about half of the circulation is over water where the Sea Surface Temperature is near 28.5°C.  In addition, the atmospheric environment is favorable for strengthening.  The upper level winds are not too strong and the vertical wind shear is moderate.  It is possible that the wind speeds could increase in the thunderstorms in the part of the circulation that is over the Atlantic Ocean on Wednesday.

The steering currents around Tropical Storm Julia are quite complicated.  There is an upper low over the Gulf of Mexico, a ridge over the western Atlantic Ocean and an upper level trough moving toward the Great Lakes and East Coast of the U.S.  The upper low and ridge over the western Atlantic combined to steer Julia mainly toward the north-northwest on Tuesday.  At times the asymmetric circulation and the upper level divergence to the east of the circulation caused the center to move east as well.  It is likely that this motion will continue on Wednesday.  The center of Julia could move very close to the coast of Georgia.  If the center remains inland, then Tropical Storm Julia will start to weaken slowly.  If the center moves over the water, then it could intensify and persist longer.

The primary risk posed by Tropical Storm Julia will be locally heavy rain and the potential for flash flooding.  Winds and waves along the coast will cause rip currents and some beach erosion.  Water rises of several feet (one meter) will be possible.

Hurricane Joaquin Passing Northwest of Bermuda

Hurricane Joaquin is bringing tropical storm force winds to Bermuda as the core of the hurricane moves northwest of that island.  Wind gusts to 64 m.p.h. have been reported in recent hours in Bermuda.  At 11:00 p.m. EDT on Sunday the center of Hurricane Joaquin was located at latitude 33.1°N and longitude 65.5°W which put it about 70 miles (110 km) northwest of Bermuda.  Joaquin was moving toward the north-northeast at 13 m.p.h. (20 km/h).  The maximum sustained wind speed was 85 m.p.h. (140 km/h) and there were wind gusts to 100 m.p.h. (160 km/h).  The minimum surface pressure was 961 mb.  A Hurricane Warning remains in effect for Bermuda.

Hurricane Joaquin is gradually moving over cooler water, but it is still over water where the Sea Surface Temperature is around 28°C.  It appears that a combination of drier air and vertical wind shear caused Joaquin to weaken on Sunday.  Thunderstorms are not rising as far up into the atmosphere and gaps have appeared in the eyewall.  Southwesterly winds in the upper levels are inhibiting upper level divergence in that portion of the hurricane and the pressure rose 17 mb on Sunday.  The wind shear could lessen for a time on Monday and the rate of weakening could slow.

Hurricane Joaquin is moving toward the north-northeast.  When it moves farther north, it will encounter the upper level westerlies in the middle latitudes.  Those westerly winds will carry Joaquin toward the east.  Joaquin could make a transition to a strong extratropical storm and affect western Europe in a few days.

Hurricane Joaquin Heading Toward Bermuda

After intensifying to almost Category 5 on the Saffir-Simpson Scale on Saturday, Hurricane Joaquin headed toward Bermuda.  The Bermuda Weather Service has issued a Hurricane Warning for Bermuda.  At 11:00 p.m. EDT on Saturday the center of Hurricane Joaquin was located at latitude 28.0°N and longitude 68.9°W which put it about 385 miles (620 km) southwest of Bermuda.  Joaquin was moving toward the northeast at 20 m.p.h. (32 km/h).  The maximum sustained wind speed was 130 m.p.h. (215 km/h) and there were wind gusts to 160 m.p.h. (260 km/h).  The minimum surface pressure was 944 mb.  Joaquin was a Category 4 hurricane on the Saffir-Simpson Scale.  The Hurricane Intensity Index (HII) was 25.1.  The Hurricane Size Index (HSI) was 20.0 and the Hurricane Wind Intensity Size Index (HWISI) was 45.1.

Joaquin is moving over water where the Sea Surface Temperature is near 29°C.  However, a large upper level trough over the southeastern U.S. and an upper level low northwest of Joaquin are combining to generate westerly winds over the hurricane.  The vertical wind shear is causing the circulation to become more asymmetrical and the strongest convection is occurring in the eastern half of the circulation.  The flow of air is also pushing drier air toward the core of Hurricane Joaquin.  If Joaquin can move fast enough to outrun the drier air, it could weaken slowly.  However, if the drier air gets into the core of the circulation, then Joaquin will weaken faster.

The trough and upper level low are steering Hurricane Joaquin quickly toward the northeast and that motion is expected to continue on Sunday.  On its anticipated track Joaquin will pass near Bermuda on Sunday night.  It could bring strong winds and a storm surge as it moves past the island.

Hurricane Joaquin Moving Slowly Away from the Bahamas

Hurricane Joaquin turned northward on Friday and it is starting to move slowly away from the Central Bahamas.  However, it is still producing strong winds, heavy rain and storm surges on San Salvador and nearby islands.  At 5:00 p.m. EDT on Friday the center of Hurricane Joaquin was located at latitude 24.1°N and longitude 74.7°W which put it about 15 miles (25 km) west-northwest of San Salvador in the Central Bahamas and about 745 miles (1200 km) south of Cape Hatteras, North Carolina.  Joaquin was moving toward the north at 7 m.p.h. (11 km/h).  The maximum sustained wind speed was 125 m.p.h. (205 km/h)  which made Joaquin a Category 3 hurricane on the Saffir-Simpson Scale.  There were wind gusts to 155 m.p.h. (250 km/h) and the minimum surface pressure was 942 mb.  The Hurricane Intensity Index (HII) was 23.6.  The Hurricane Size Index (HSI) was 20.3 and the Hurricane Wind Intensity Size Index (HWISI) was 43.9.

A Hurricane Warning is in effect for the Central Bahamas including Cat Island, the Exumas, Rum Cay, Long Island and San Salvador.  A Hurricane Warning is in effect for the Northwestern Bahamas including the Abacos, Berry Island, Eleuthera, Grand Bahama Island and New Providence.  A Hurricane Watch has been issued for Bimini and Andros Island.  A Tropical Storm Warning is in effect for Andros Island and the Southeastern Bahamas including the Acklins, Crooked Island, Long Cay, the Inaguas, Mayaguana, the Ragged Islands and the Turks and Caicos.  A Tropical Storm Watch has been issued for Bermuda.

Hurricane Joaquin did not change a lot on Friday, although there were some indications that vertical wind shear may be starting to affect it.  Microwave satellite imagery and aerial reconnaissance indicate that there is still and eye, although the eyewall is thinner on the north side.  Most of the stronger thunderstorms are on the southern side of the circulation.  An upper level trough over the eastern U.S. may be creating stronger winds that are hitting Joaquin from the southwest.  Those southwesterly winds may be limiting upper level divergence on that side of the hurricane.  The hurricane is still over water where the Sea Surface Temperature is near 30°C.  So, vertical wind shear is the only factor inhibiting intensification.  The trough is expected to produce more vertical wind shear on Saturday, which could start to weaken Joaquin.

The upper level trough is starting to steer Joaquin slowly toward the north.  The trough is expected to steer Joaquin toward the northeast at a faster rate during the next several days.  Guidance from all of the numerical models has come into agreement that Joaquin will stay east of the U.S.  Conditions in the Central Bahamas should improve on Saturday as Hurricane Joaquin moves farther away.  The possibility that Joaquin could be near to Bermuda on Sunday prompted the issuance of a Tropical Storm Watch for that island.