Barbara Weakens to a Tropical Storm

Former Hurricane Barbara weakened to a tropical storm on Friday.  At 5:00 p.m. EDT on Friday the center of Tropical Storm Barbara was located at latitude 18.6°N and longitude 134.7°W which put it about 1330 miles (2145 km) east of Hilo, Hawaii.  Barbara was moving toward the west-northwest at 13 m.p.h. (20 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 997 mb.

The effects of vertical wind shear and cooler Sea Surface Temperatures caused former Hurricane Barbara to weaken quickly to a tropical storm on Friday.  An upper level trough northeast of Hawaii produced strong southwesterly winds which blew the upper portion of the circulation north of the remainder of the tropical storm.  In addition, Tropical Storm Barbara moved over water where the Sea Surface Temperature was near 25°C which meant there was less energy to support the development of taller thunderstorms.  Tropical Storm Barbara still had a well formed circulation in the lower levels of the atmosphere.  However, as a result of the strong shear and cooler water, bands consisted primarily of showers and lower clouds.  Winds to tropical storm force extended out about 140 miles (220 km) from the center of circulation.

Tropical Storm Barbara will continue to move over cooler water and through a region of strong vertical wind shear during the next several days.  Barbara will continue to weaken and it could be a tropical depression on Saturday.

Since Tropical Storm Barbara contains few tall thunderstorms, it is being steered by winds closer to the surface.  A subtropical high pressure system north of Barbara will steer the tropical storm toward the west.  On its anticipated track Tropical Storm Barbara will move toward Hawaii.

Hurricane Barbara Starts to Weaken

Hurricane Barbara started to weaken on Wednesday when it moved over cooler water well to the east of Hawaii.  At 5:00 p.m. EDT on Wednesday the center of Hurricane Barbara was located at latitude 14.3°N and longitude 127.5°W which put it about 1860 miles (2990 km) east of Hilo, Hawaii.  Barbara was moving toward the west-northwest at 12 m.p.h. (19 km/h).  The maximum sustained wind speed was 140 m.p.h. (220 km/h) and there were wind gusts to 170 m.p.h. (275 km/h).  The minimum surface pressure was 941 mb.

The circulation around Hurricane Barbara remained very well organized.  There was a circular eye 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.  Several bands of showers and thunderstorms were revolving around the core of Hurricane Barbara.  Storms near the core of the circulation were generating strong upper level divergence which was pumping mass away from the hurricane.  Winds to hurricane force extended out about 45 miles (75 km) from the center of circulation.  Winds to tropical storm force extended out about 185 miles (295 km) from the center.

Hurricane Barbara still rated at Category 4 on the Saffir-Simpson Scale.  The Hurricane Intensity Index (HII) for Barbara was 28.3.  The Hurricane Size Index (HSI) was 16.5 and the Hurricane Wind Intensity Size Index (HWISI) was 44.8.

Hurricane Barbara will gradually move into an environment less capable of supporting a strong hurricane during the next few days.  Barbara will move over water where the Sea Surface Temperature is near 26°C.  As a result, Hurricane Barbara will extract less energy from the upper ocean and it will gradually weaken.  Barbara will move closer to an upper level trough located northeast of Hawaii.  When Hurricane Barbara gets closer to the trough later this week, stronger upper level southwesterly winds will create more vertical wind shear and the hurricane will weaken more quickly.

Hurricane Barbara will move south of a subtropical ridge over the Eastern North Pacific Ocean.  The ridge will steer Barbara toward the west-northwest during the next 24 to 36 hours.  The ridge is forecast to strengthen on Friday and it will steer Hurricane Barbara more toward the west when that happens.  On its anticipated track Barbara could approach Hawaii in about five days.  It will be much weaker by that time.

Tropical Storm Mun Develops Near Hainan Island

Tropical Storm Mun developed near Hainan Island on Tuesday when the Japan Meteorological Agency designated an area of low pressure as a tropical storm.  At 5:00 p.m. EDT on Tuesday the center of Tropical Storm Mun was located at latitude 19.4°N and longitude 109.8°E which put the center over Hainan Island and it was about 225 miles (365 km) east-southeast of Hai Phong, Vietnam.  Mun was moving toward the west 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 994 mb.

The circulation around Tropical Storm Mun was very large but it did not have a well developed inner core.  Winds to tropical storm force extended out several hundred miles from the center of circulation.  However, there were few thunderstorms near the center.  The strongest thunderstorms were in two bands in the western periphery of the circulation.  Other bands around Tropical Storm Mun consisted primarily of showers and lower clouds.

Tropical Storm Mun will move through an environment that is not favorable for intensification.  After Mun moves west of Hainan Island the tropical storm will move over water where the Sea Surface Temperature is near 30°C.  So, there is plenty of energy in the upper ocean to support intensification.  However, Tropical Storm Mun will move south of an upper level ridge over eastern Asia.  The ridge will produce strong northeasterly winds which will cause strong vertical wind shear.  The wind shear will prevent significant intensification of Tropical Storm Mun.

Since Tropical Storm Mun does not have a well developed inner core with tall thunderstorms, it will be steered by the winds at lower levels in the atmosphere.  Southeasterly winds blowing as part of the monsoonal circulation will push Mun toward the border between Vietnam and China.  On its anticipated track the center of Tropical Storm Mun will move inland within 24 hours.  Mun will bring some gusty winds and locally heavy rain to portions of northeastern Vietnam and southeastern China.  Heavy rain could cause flash floods in some locations.

Barbara Rapidly Intensifies Into a Major Hurricane

Hurricane Barbara rapidly intensified into a major hurricane on Tuesday as it moved over the Eastern North Pacific Ocean between Baja California and Hawaii.  At 11:00 a.m. EDT on Tuesday the center of Hurricane Barbara was located at latitude 12.5°N and longitude 122.2°W which put it about 1080 miles (1740 km) southwest of the southern tip of Baja California.  Barbara was moving toward the west-northwest at 14 m.p.h. (22 km/h).  The maximum sustained wind speed was 130 m.p.h. (215 km/h) and there were wind gusts to 150 m.p.h. (240 km/h).  The minimum surface pressure was 948 mb.

Hurricane Barbara continued to intensify rapidly on Tuesday.  A circular eye became more evident on satellite imagery.  The eye was surrounded by a ring of strong thunderstorms and the strongest winds were occurring in that ring of storms.  Storms near the core of Barbara were generating strong upper level divergence which was pumping mass away from the hurricane in all directions.  Multiple bands of showers and thunderstorms were revolving around the core of Hurricane Barbara.  Winds to hurricane force extended out about 25 miles (40 km) from the center of circulation.  Winds to tropical storm force extended out about 200 miles (320 km) in the southeastern quadrant of the circulation.  Tropical storm force winds extended out about 120 miles (195 km) from the center in the other three quadrants.

Hurricane Barbara was at Category 4 on the Saffir-Simpson Scale.  The Hurricane Intensity Index (HII) for Barbara was 25.1.  The Hurricane Size Index (HSI) was 11.0 and the Hurricane Wind Intensity Size Index (HWISI) was 36.1.

Hurricane Barbara will move through an environment very favorable for strong hurricanes for another 12 to 24 hours.  Barbara will move over water where the Sea Surface Temperature is near 28°C.  It will move through an area where the upper level winds are weak and there will be little vertical wind shear.  Hurricane Barbara is likely to intensify further during the next 12 hours.  If a rainband wraps around the existing eye and eyewall, then an eyewall replacement cycle could cause Barbara to weaken.  Hurricane Barbara will approach cooler water on Wednesday and it is likely to start to weaken by that time.  Barbara will move into an area where the upper level winds are stronger later this week and it could weaken more quickly when the wind shear increases.

Hurricane Barbara will move south of a subtropical ridge over the Eastern North Pacific Ocean.  The ridge will steer Barbara in a west-northwesterly direction during the next several days.  On its anticipated track Hurricane Barbara will move in the general direction of Hawaii.

Barbara Rapidly Intensifies Into a Hurricane

Former Tropical Storm Barbara rapidly intensified into a hurricane over the Eastern North Pacific Ocean on Monday.  At 5:00 p.m. EDT on Monday the center of Hurricane Barbara was located at latitude 11.5°N and longitude 118.5°W which put it about 970 miles (1560 km) southwest of the southern tip of Baja California.  Barbara was moving toward the west at 16 m.p.h. (26 km/h).  The maximum sustained wind speed was 85 m.p.h. (135 km/h) and there were wind gusts to 100 m.p.h. (160 km/h).  The minimum surface pressure  was 983 mb.

Hurricane Barbara intensified rapidly on Monday.  An eye formed at the center of circulation and a ring of strong thunderstorms surrounded the eye.  The strongest winds were occurring in that ring of storms.  Bands of showers and thunderstorms were revolving around the core of the circulation.  Storm near the core of Barbara were generating strong upper level divergence which was pumping mass away from the hurricane.  Winds to hurricane force extended out about 25 miles (40 km) from the center of circulation.  Winds to tropical storm force extended out about 160 miles (260 km) from the center.

Hurricane Barbara will move through an environment very favorable for intensification during the next 36 to 48 hours.  Barbara 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 Barbara will continue to intensify rapidly and it is expected to strengthen into a major hurricane on Tuesday.

Hurricane Barbara will move south of a subtropical ridge over the Eastern North Pacific Ocean during the next few days.  The ridge will steer Barbara toward the west-northwest.  On its anticipated track Hurricane Barbara will move farther away from Baja California and the rest of Mexico.

Tropical Storm Barbara Forms South of Baja California

Tropical Storm Barbara formed south of Baja California on Sunday as the remnants of former Hurricane Alvin were dissipating over the Eastern North Pacific Ocean.  At 11:00 a.m. EDT on Sunday the center of Tropical Storm Barbara was located at latitude 10.6°N and longitude 110.4°W which put it about 850 miles (1370 km) south of the southern tip of Baja California.  Barbara was moving toward the west-northwest at 16 m.p.h. (26 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.

More thunderstorms developed near the center of a low pressure system south of Baja California on Sunday and the National Hurricane Center designated the system as Tropical Storm Barbara.  Bands of showers and thunderstorms were revolving around the center of circulation.  Storms near the center were generating upper level divergence which was pumping mass away from the tropical storm.  Tropical Storm Barbara was larger than former Hurricane Alvin.  Winds to tropical storms force extended out about 80 miles (130 km) from the center of circulation.

Tropical Storm Barbara will move through an environment favorable for intensification during the next several days.  Barbara will move over water where the Sea Surface Temperature is near 29°C.  It will move through an area where the upper level winds are weak and there will be little vertical wind shear.  Tropical Storm Barbara will continue to intensify and it is likely to strengthen into a hurricane by the middle of the week.  Barbara could intensify rapidly when the inner core is more developed.

Tropical Storm Barbara will move south of a subtropical ridge over the Eastern North Pacific Ocean.  The ridge will steer Barbara toward the west-northwest.  On its anticipated track Tropical Storm Barbara will move away from Baja California and the rest of Mexico.

Alvin Strengthens Into a Hurricane Southwest of Baja California

Former Tropical Storm Alvin strengthened into a hurricane southwest of Baja California on Thursday evening.  At 11:00 p.m. EDT on Thursday the center of Hurricane Alvin was located at latitude 17.4°N and longitude 115.4°W which put it about 520 miles (840 km) southwest of the southern tip of Baja California.  Alvin was moving toward the northwest at 16 m.p.h. (26 km/h).  The maximum sustained wind speed was 75 m.p.h. (120 km/h) and there were wind gusts to 90 m.p.h. (145 km/h).  The minimum surface pressure was 992 mb.

The circulation around Hurricane Alvin exhibited much greater organization on Wednesday.  A small circular eye with a diameter of 10 miles (15 km) appeared 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.  The circulation around Hurricane Alvin was very small.  Winds to hurricane force extended out only 10 miles (15 km) from the center of circulation.  Winds to tropical storm force extended out about 50 miles (80 km) from the center.

Hurricane Alvin may be near its maximum intensity.  Alvin was moving over water where the Sea Surface Temperature was near 27°C.  However, it will move over cooler water on Friday.  The small size of the circulation around Hurricane Alvin could allow it to weaken quickly once it moves over the cooler water.

Hurricane Alvin will move near the western end of a subtropical ridge over Eastern North Pacific Ocean.  The ridge will steer Alvin toward the west-northwest during the next several days.  On its anticipated track Hurricane Alvin is forecast to weaken when it moves over colder water between Baja California and Hawaii.

Tropical Storm Sepat Forms Near Honshu

Tropical Storm Sepat formed near Honshu on Thursday.  More thunderstorms formed near the center of a low pressure system near the southeast coast of Honshu on Thursday and the Japan Meteorological Agency designated the system as Tropical Storm Sepat.  At 8:00 a.m. EDT on Thursday the center of Tropical Storm Sepat was located at latitude 32.6°N and longitude 134.7°E which put it about 100 miles (160 km) southwest of Susami, Japan.  Sepat was moving toward the northeast at 32 m.p.h. (50 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.

The distribution of thunderstorms around Tropical Storm Sepat was asymmetrical.  The strongest thunderstorms were in several bands south and east of the center of circulation.  Bands in the other parts of the circulation consisted primarily of showers and lower clouds.  Storms southeast of the center of Sepat were generating upper level divergence which was pumping mass away to the northeast of the tropical storm.  Winds to tropical storm force extended out about 150 miles (240 km) to the east of the center of circulation.

Tropical Storm Sepat will move through an environment marginally favorable for intensification during the next 12 to 24 hours.  Sepat will move over water where the Sea Surface Temperature is near 24°C.  An upper level trough west of Japan will produce strong southwesterly winds which will blow toward the top of the circulation.  Those winds will cause moderate vertical wind shear, which is the primary reason for the asymmetrical distribution of thunderstorms.  Moderate vertical wind shear and cooler water will cause the structure of Tropical Storm Sepat to change to that of an extratropical cyclone.  Sepat could strengthen during the extratropical transition because upper level divergence will cause the surface pressure to decrease.

The upper level trough will steer Tropical Storm Sepat rapidly toward the northeast.  On its anticipated track the center of Tropical Storm Sepat will pass near the coast of Honshu.  Sepat will bring gusty winds and it could drop locally heavy rain.

Tropical Storm Alvin Develops South of Baja California

Tropical Storm Alvin developed south of Baja California on Wednesday morning, when former Tropical Depression One-E strengthened to a tropical storm.  At 11:00 a.m. EDT on Wednesday the center of Tropical Storm Alvin was located at latitude 14.7°N and longitude 109.4°W which put it about 565 miles (915 km) south of the southern tip of Baja California.  Alvin was moving toward the west at 14 m.p.h. (22 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.

The circulation around Tropical Storm Alvin exhibited greater organization on Wednesday morning.  A band of thunderstorms wrapped around the eastern side of the center of circulation.  Other bands of showers and thunderstorms were organizing in the eastern half of the circulation.  Winds to tropical storm force extended out about 35 miles (55 km) from the center on the eastern side of the circulation.  Bands in the western half of the circulation consisted primarily of showers and lower clouds.  Storms near the center were generating upper level divergence which was pumping mass away from the tropical storm.

Tropical Storm Alvin will move through an environment favorable for intensification during the next 24 to 36 hours.  Alvin will move over water where the Sea Surface Temperature is near 28°C.  Tropical Storm Alvin will move south of an upper level ridge.  The ridge will produce northeasterly 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 Storm Alvin will intensify during the next day or two and it could strengthen into a hurricane.

The upper level ridge will steer Tropical Storm Alvin toward the west during the next several days.  Alvin could move a little to the south of due west during the next 24 hours.  On its anticipated track Tropical Storm Alvin will move steadily farther away from Mexico.

Tropical Depression One-E Forms West of Mexico

Tropical Depression One-E formed west of Mexico on Tuesday afternoon.  More thunderstorms developed close to the center of a low pressure system over the Eastern North Pacific Ocean and the National Hurricane Center designated the system as Tropical Depression One-E.  At 5:00 p.m. EDT on Tuesday the center of Tropical Depression One-E was located at latitude 15.2°N and longitude 105.7°W which put it about 280 miles (450 km) south-southwest of Manzanillo, Mexico.  The depression was moving toward the west-northwest at 15 m.p.h. (24 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 1007 mb.

The circulation around Tropical Depression One-E exhibited greater organization on Tuesday afternoon.  Several short bands of showers and thunderstorms were developing near the center of circulation.  One band was north of the center, another was west of the center and a third band was south of the center of circulation.  Bands east of the center consisted primarily of showers and lower clouds.  Thunderstorms near the center of circulation were beginning to generate upper level divergence which was pumping mass away from the tropical depression.

Tropical Depression One-E will move through an environment favorable for intensification during the next day or two.  The depression will move over water where the Sea Surface Temperature is near 28°C.  It will move south of an upper level ridge over Mexico and the Eastern North Pacific Ocean.  The ridge will produce northeasterly winds which will blow toward the top of the circulation.  Those winds will cause some vertical wind shear which will slow the rate of intensification, but the shear will not be strong enough to prevent intensification.  Tropical Depression One-E is likely to intensify into a tropical storm during the next 24 to 36 hours.

A subtropical ridge north of Tropical Depression One-E will steer the depression toward the west-northwest.  On its anticipated track Tropical Depression One-E will move away from Mexico.  It is forecast to pass south of Baja California.