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Tropical Storm Leepi Forms Southeast of Iwo To

Tropical Storm Leepi formed southeast of Iwo To on Saturday.  At 5:00 p.m. EDT on Saturday the center of Tropical Storm Leepi was located at latitude 21.5°N and longitude 142.7°W which put it about 285 miles (465 km) south-southeast of Iwo To.  Leepi was moving toward the north-northwest at 12 m.p.h. (19 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 995 mb.

A distinct center of circulation developed within an area of thunderstorms between the Northern Marianas and Iwo To and the Japan Meteorological Agency designated the system as Tropical Storm Leepi.  The distribution of thunderstorms around Tropical Storm Leepi was very asymmetrical.  The stronger thunderstorms were all occurring in bands in the eastern half of the circulation.  The bands in the western half of the circulation consisted of showers and low clouds.  Storms near the center of Leepi were generating upper level divergence which was pumping mass away to the northeast of the tropical storm.

Tropical Storm Leepi will move through an environment somewhat favorable for intensification during the next 12 to 24 hours.  Leepi will move over water where the Sea Surface Temperature is near 29°C.  An upper level trough northeast of the tropical storm was producing southwesterly winds which were causing moderate vertical wind shear.  The wind shear was inhibiting the divergence to the west of Tropical Storm Leepi.  The tropical storm also appeared to be drawing drier air into the western side of the circulation.  Leepi could intensify on Sunday, but it will move into an area of stronger upper level winds in a day or so.  Increased vertical wind shear will likely start to weaken Tropical Storm Leepi after that occurrs.

Tropical Storm Leepi will move near the western end of a ridge in the middle troposphere.  The ridge will Leepi in a general motion toward the northwest.  On its anticipated track Tropical Storm Leepi will move near Iwo To in about 24 hours.  Leepi could approach the northern Ryukyu Islands and Kyushu in about three days.

Elsewhere over the Western North Pacific, Tropical Storm Yagi passed over the southern Ryukyu Islands on Saturday.  At 5:00 p.m. EDT on Saturday the center of Tropical Storm Yagi was located at latitude 25.6°N and longitude 124.8°E which put it about 250 miles (400 km) east of Taipei, Taiwan.  Yagi 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 993 mb.

Hurricane Hector Passes South of Hawaii

Powerful Hurricane Hector passed south of Hawaii on Wednesday.  At 11:00 p.m. EDT on Wednesday the center of Hurricane Hector was located at latitude 16.7°N and longitude 156.8°W which put it about 325 miles (525 km) south-southeast of Honolulu, Hawaii.  Hector was moving toward the west at 16 m.p.h. (26 km/h).  The maximum sustained wind speed was 115 m.p.h. (185 km/h) and there were wind gusts to 135 m.p.h. (220 km/h).  The minimum surface pressure was 959 mb.

The circulation of Hurricane Hector remained circular and symmetrical.  Information from radar and satellites indicated that Hurricane Hector had a double eyewall structure.  There was a small inner eye surrounded by an inner eyewall.  The inner eyewall was thin and it appeared to be weakening.  A clear area, sometimes called a moat, surrounded the inner eyewall.  A second thicker eyewall surrounded the moat.  Several shorter bands of of showers and thunderstorms were revolving around the core of Hector.  The circulation of Hurricane Hector was relatively small.  Winds to hurricane force extended out about 35 miles (55 km) from the center of circulation.  Winds to tropical storm force only extended out about 95 miles (155 km) from the center.

Hurricane Hector exhibited a structure that is sometimes called an annular hurricane.  Annular hurricanes often achieve an equilibrium with their environment which can persist for days if there is not much wind shear.  Hector will move over water where the Sea Surface Temperature is between 27°C and 28°C.  It will move through a region where there is little vertical wind shear.  Hurricane Hector will remain a strong hurricane and it could strengthen during the next 24 to 48 hours, if the inner eyewall dissipates completely.

Hurricane Hector will move south of the subtropical high pressure system over the Central Pacific.  The high will steer Hector toward the west for several more days.  On its anticipated track Hurricane Hector will remain south of Hawaii.

Elsewhere over the Eastern North Pacific Ocean, Hurricane John weakened west of Baja California and Tropical Storm Kristy exhibited little change on Wednesday.  At 11:00 p.m. EDT on Wednesday the center of Hurricane John was located at latitude 23.1°N and longitude 114.4°W which put it about 285 miles (460 km) west of the southern tip of Baja California.  John was moving toward the northwest at 16 m.p.h. (26 km/h).  The maximum sustained wind speed was 80 m.p.h. (130 km/h) and there were wind gusts to 95 m.p.h. (155 km/h).  The minimum surface pressure was 983 mb.

At 11:00 p.m. EDT on Wednesday the center of Tropical Storm Kristy was located at latitude 15.3°N and longitude 130.0°W which put it about 1410 miles (2220 km) west-southwest of the southern tip of Baja California.  Kristy was moving toward the northwest at 7 m.p.h. (11 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 1002 mb.

Typhoon Shanshan Brushes East Coast of Honshu

Typhoon Shanshan brushed the east coast of Honshu late on Wednesday.  At 11:00 p.m. EDT on Wednesday the center of Typhoon Shanshan was located at latitude 36.8°N and longitude 141.5°E which put it about 40 miles (65 km) east of Iwaki, Japan.  Shanshan was moving toward the north at 12 m.p.h. (19 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 975 mb.

The center of Typhoon Shanshan moved very close to the east coast of Honshu near Choshi on Wednesday and then it moved nearly parallel to the coast.  The stronger winds and heavier rain were occurring on the eastern side of Shanshan, and they passed east of Honshu.  The winds were weaker and the rain was lighter in the western side of Typhoon Shanshan.  Winds to tropical storm force were occurring near the east coast of Honshu.  The typhoon had little effect on the weather near Tokyo.  Some locations near the coast did have a period of heavier rain after the center of Typhoon Shanshan passed and the winds blew from the southwest toward the coast.

Typhoon Shanshan will affect the coast of Honshu for another six to twelve hours, while the center moves nearly parallel to the coast.  Shanshan will reach an area where stronger westerly winds are blowing in the middle and upper troposphere.  Those winds will turn Typhoon Shanshan toward the east and they will push it away from Japan.  The stronger winds will also cause significant vertical wind shear.  Shanshan will move over cooler water when it turns eastward.  The combination of vertical wind shear and cooler water will cause Typhoon Shanshan to weaken and it could make a transition to an extratropical cyclone in a day or two.

Elsewhere over the Western North Pacific, Tropical Storm Yagi formed southeast of Okinawa on Wednesday.  At 11:00 p.m. EDT the center of Tropical Storm Yagi was located at latitude 21.3°N and longitude 133.6°E which put it about 530 miles (855 km) southeast of Okinawa.  Yagi was moving toward the northwest at 7 m.p.h. (11 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 993 mb.

Debby Makes a Transition to a Tropical Storm

Former Subtropical Storm Debby made a transition to a tropical storm on Wednesday.  At 11:00 a.m. EDT on Wednesday the center of Tropical Storm Debby was located at latitude 41.2°N and longitude 48.3°W which put it about 1150 miles (1855 km) west-northwest of the Azores.  Debby was moving toward the northeast at 12 m.p.h. (19 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 1003 mb.

The structure of former Subtropical Storm Debby changed on Wednesday and it exhibited the characteristics of a tropical storm.  More thunderstorms formed around the center of circulation and those thunderstorms rose higher into the atmosphere.  Additional bands of showers and thunderstorms developed and revolved around the core of the circulation.  Storms near the core began to generate upper level divergence.  The strongest winds occurred closer to the center of circulation.  The National Hurricane Center designated Debby as a tropical storm based on information from satellites.

Tropical Storm Debby will move into an environment unfavorable for a tropical storm during the next 24 to 48 hours.   Debby was over water where the Sea Surface Temperature was near 26°C, but it will soon move over much cooler water.  It will start to weaken when it moves over the cooler water.  It could take several days for the circulation around Tropical Storm Debby to spin down.

Tropical Storm Debby will be steered toward the northeast as it moves between an upper level trough to the west and an upper level ridge to the east.  On its anticipated track Tropical Storm Debby will move between the Azores and Greenland.

Hurricane Hector Prompts Tropical Storm Warning for Hawaii

The imminent approach of Hurricane Hector prompted the issuance of a Tropical Storm Warning for Hawaii County.  At 11:00 p.m. EDT on Tuesday the center of Hurricane Hector was located at latitude 16.6°N and longitude 150.7°W which put it about 370 miles (590 km) east-southeast of South Point, Hawaii.  Hector was moving toward the west at 16 m.p.h. (26 km/h).  The maximum sustained wind speed was 130 m.p.h. (215 km/h) and there were wind gusts to 155 m.p.h. (250 km/h).  The minimum surface pressure was 952 mb.

The circulation of Hurricane Hector remains very well organized and it seems to have reached an equilibrium with its environment.  There is a circular eye at the center of circulation.  The eye is surrounded by a ring of strong thunderstorms and the strongest winds are occurring in that rings of storms.  Several bands of showers and thunderstorms are revolving around the core of Hurricane Hector.  Storms around the core were generating well developed upper level divergence was pumping mass away from the hurricane.  Winds to hurricane force extended out about 40 miles (65 km) from the center of circulation.  Winds to tropical storm force extended out about 115 miles (185 km) from the center.

Hurricane Hector will remain in a favorable environment for several more days.  Hector will move over water where the Sea Surface Temperature is near 27°C.  It will move through a region where the upper level winds are weak and there will be little vertical wind shear.  Hurricane Hector will remain a strong hurricane for the next few days.

Hurricane Hector will move south of the subtropical ridge over the Central Pacific Ocean.  The ridge will steer Hector in a general westerly direction for several more days.  On its anticipated track the center of Hurricane Hector will pass south of Hawaii.  However, rainbands on the north side of Hector could bring winds to tropical storm force to the Big Island of Hawaii, which is why the Tropical Storm Warning was issued for Hawaii County.

Typhoon Shanshan Moves Closer to Honshu

Typhoon Shanshan moved steadily closer to Honshu on Tuesday.  At 11:00 p.m. EDT on Tuesday the center of Typhoon Shanshan was located at latitude 33.7°N and longitude 141.6°E which put it about 190 miles (305 km) southeast of Tokyo.  Shanshan was moving toward the north-northwest at 12 m.p.h. (19 km/h).  The maximum sustained wind speed was 90 m.p.h. (145 km/h) and there were wind gusts to 115 m.p.h. (185 km/h).  The minimum surface pressure was 965 mb.

Typhoon Shanshan intensified earlier on Tuesday and it started to weaken on Tuesday night.  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 Typhoon Shanshan.  The rainbands south and east of the center were stronger and the rainbands north and west of the center were weaker.  Storms near the core of Shanshan were generating upper level divergence which was pumping mass away from typhoon.  Winds to typhoon force extended out about 45 miles (75 km) from the center of circulation.  Winds to tropical storm force extended out about 220 miles (350 km) from the center.

Typhoon Shanshan will move through an environment on Wednesday that should allow it to remain a typhoon until it reaches Japan.  Shanshan will move over water where the Sea Surface Temperature is near 28°C.  It will move through a region where the upper level winds are weaker and there will be little vertical wind shear.  Typhoon Shanshan will move into a region in a day or so where stronger upper level winds will blow from the west.  Vertical wind shear will increase at that time and Typhoon Shanshan will start to weaken more quickly.

Typhoon Shanshan will move around the western end of a ridge over the North Pacific Ocean and the ridge will steer the typhoon toward the north on Wednesday.  When Shanshan gets close to the coast of Honshu, the westerly winds will turn the typhoon toward the east.  On its anticipated track Typhoon Shanshan could make landfall on the coast of Honshu east of Tokyo in 18 to 24 hours.  Shanshan will bring gusty winds and it could drop heavy rain over coastal regions of eastern Honshu.

Hurricane John Absorbs Ileana, Tropical Storm Kristy Forms

The much stronger and larger circulation of Hurricane John absorbed the smaller and weaker Tropical Storm Ileana south of Baja California on Tuesday morning, while Tropical Storm Kristy formed farther west over the Eastern North Pacific Ocean.  At 5:00 p.m. EDT on Tuesday the center of Hurricane John was located at latitude 18.7°N and longitude 110.5°W which put it about 295 miles (470 km) south of the southern tip of Baja California.  John was moving toward the northwest at 10 m.p.h. (17 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 969 mb.

The circulation of Hurricane John is well organized.  A circular eye is at the center of circulation.  A ring of stronger thunderstorms wraps around the eye.  The strongest storms are in the eastern half of the ring and that is where the strongest winds are occurring.  Several bands of showers and thunderstorms are revolving around the core of Hurricane John.  The strongest bands are south and east of the center of circulation.  The bands north and west of the center are weaker and there is cooler water in that area.  Storms around the core of the circulation are generating strong upper level divergence which is pumping mass away from the hurricane.

Hurricane John will move through an environment favorable for intensification on Wednesday.  John 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.  Hurricane John could intensify on lWednesday and it has a chance to strengthen into a major hurricane.  John will start to move over cooler water in 24 to 36 hours and it will start to weaken when that happens.

Hurricane John will move around the western side of a ridge in the middle troposphere.  The ridge will steer John toward the northwest during the next day or two.  On its anticipated track the core of Hurricane John will pass west of Baja California.  Rainbands north of the center of Hurricane John could drop locally heavy rain over parts of Baja California and there will be a risk of flash floods.  Hurricane John could push higher surf along the west coast of Baja California toward southern California.

Elsewhere over the Eastern North Pacific, Tropical Storm Kristy formed southwest of Hurricane John on Tuesday morning.  At 5:00 p.m. EDT on Tuesday the center of Tropical Storm Kristy was located at latitude 13.7°N and longitude 127.1°W which put it about 1290 miles (2080 km) west-southwest of the southern tip of Baja California.  Kristy was moving toward the west 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 1000 mb.  There is much uncertainty about whether or not the circulation of Tropical Storm Kristy will be affected by the circulation of Hurricane John.

Subtropical Storm Debby Forms West of the Azores

Subtropical Storm Debby formed over the North Atlantic Ocean west of the Azores on Tuesday morning.  At 11:00 a.m. EDT on Tuesday the center of Subtropical Storm Debby was located at latitude 38.9°N and longitude 48.5°W which put it about 1160 miles (1870 km) west of the Azores.  Debby was moving toward the north 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 1008 mb.

A surface low pressure system revolved around the western side of an upper level low over the North Atlantic Ocean during the past few days.  More bands of showers and thunderstorms developed around the surface low on Tuesday morning and its circulation become more circular.  The National Hurricane Center designated the low pressure system as Subtropical Storm Debby based on satellite imagery.  The strongest winds were occurring in a rainband that wrapped around the northern side of the circulation.  Bands south of the center of circulation consisted primarily of showers and lower clouds.

Subtropical Storm Debby will move through an environment somewhat favorable for intensification during the next 24 hours.  Debby will move over water where the Sea Surface Temperature is between 26°C and 27°C.  Subtropical Storm Debby will move between an upper level trough to its west and an upper level ridge to its east.  The trough and ridge will produce southeasterly winds which will cause moderate vertical wind shear.  Subtropical Storm Debby could strengthen during the next 24 hours.  Debby will move over much colder water in about 36 hours and then it will weaken.

The upper level ridge and trough will steer Subtropical Storm Debby in a mainly northerly direction.  On its anticipated track Subtropical Storm Debby will remain west of the Azores.

Recon Finds Hurricane Hector Nearly at Category 5

An Air Force Reserve Hurricane Hunter reconnaissance aircraft found on Monday that Hurricane Hector had strengthened to nearly Category 5 on the Saffir-Simpson Scale.  At 5:00 p.m. EDT on Monday the center of Hurricane Hector was located at latitude 15.2°N and longitude 143.1°W which put it about 870 miles (1405 km) east-southeast of South Point, Hawaii.  Hector was moving toward the west at 16 m.p.h. (26 km/h).  The maximum sustained wind speed was 155 m.p.h. (250 km/h) and there were wind gusts to 190 m.p.h. (305 km/h).  The minimum surface pressure was 936 mb.  A Tropical Storm Watch is in effect for Hawaii County.

Hurricane Hector has a very symmetrical, well formed circulation.  There is a circular eye with a diameter of 19 miles (31 km) at the center of circulation.  The eye is 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 Hector.  Storms near the core were generating well developed upper level divergence which was pumping mass away from the hurricane in all directions.

The circulation of Hurricane Hector is compact.  Winds to hurricane force extend out about 35 miles (55 km) from the center of circulation.  Winds to tropical storm force extend out about 105 miles (170 km) from the center.  The Hurricane Intensity Index (HII) for Hurricane Hector is 33.3.  The Hurricane Size Index (HSI) is 12.1 and the Hurricane Wind Intensity Size Index (HWISI) is 45.4.

Hurricane Hector will remain in its current environment for several more days.  Hector will move over water where the Sea Surface Temperature is near 27°C.  It will move through a region where the upper level winds are weak and there will be little vertical wind shear.  If a rainband wraps around the eye and eyewall, then an eyewall replacement cycle could occur.  Eyewall replacement cycles cause weakening at first while the inner eyewall dissipates.  Hurricanes can restrengthen if the outer eyewall starts for move closer to the center of circulation.  Most very powerful hurricanes only stay very intense for 12 to 24 hours before they start to weaken.  If takes a lot of energy to drive an intense hurricane and if Hector moves into an environment that is a little less favorable, then it could weaken.

Hurricane Hector will move south of the subtropical high pressure system over the Eastern and Central North Pacific Ocean.  The subtropical high will steer Hector in a general westerly direction during the next few days.  On its anticipated track Hurricane Hector will be southeast of Hawaii by Wednesday morning.  The core of Hurricane Hector is forecast to pass south of Hawaii, but it could come close enough to cause tropical storm force winds which is the reason for the Tropical Storm Watch.

Typhoon Shanshan Moves Toward Japan

Typhoon Shanshan moved toward Japan on Monday.  At 11:00 a.m. EDT on Monday the center of Typhoon Shanshan was located at latitude 29.2°N and longitude 145.3°E which put it about 585 miles (940 km) southeast of Tokyo, Japan.  Shanshan was moving toward the north-northwest at 17 m.p.h. (28 km/h).  The maximum sustained wind speed was 80 m.p.h. (130 km/h) and there were wind gusts to 95 m.p.h. (155 km/h).  The minimum surface pressure was 971 mb.

Typhoon Shanshan weakened slightly during the past 24 hours.  It appeared that some drier air may have been pulled into the western half of the circulation.  There was still a circular eye at the center of circulation, but there were breaks in the ring of thunderstorms around the eye.  There were several bands of stronger storms in the eastern and southern parts of the circulation.  Bands north and west of the center of Shanshan consisted primarily of showers and lower clouds.  Storms in the core were generating strong upper level divergence which was pumping mass away from the typhoon.

Typhoon Shanshan will move through an environment that should allow it to remain a typhoon for several more days.  Shanshan 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.  Drier air north and west of Typhoon Shanshan will inhibit the formation of taller thunderstorms in that part of the typhoon and the drier air will limit the potential for intensification.

Typhoon Shanshan will move around the western side of a subtropical ridge over the North Pacific Ocean.  The ridge will steer Shanshan in a general north-northwesterly direction for another two or three days.  When Typhoon Shanshan nears Honshu, an southwesterly winds on the east side of an upper level trough will start to steer the typhoon toward the northeast.  There is still uncertainty about when and where the turn toward then northeast will occur and Typhoon Shanshan could be close to Tokyo in about three days.