Monthly Archives: September 2018

Typhoon Mangkhut Strengthens to Equivalent of a Major Hurricane

Typhoon Mangkhut strengthened into the equivalent of a major hurricane as it moved west of Guam on Monday.  At 11:00 p.m. EDT on Monday the center of Typhoon Mangkhut was located at latitude 14.0°N and longitude 140.6°E which put it about 230 miles (375 km) west of Guam.  Mangkhut was moving toward the west at 16 m.p.h. (26 km/h).  The maximum sustained wind speed was 140 m.p.h. (225 km/h) and there were wind gusts to 165 m.p.h. (270 km/h).  The minimum surface pressure was 939 mb.  Typhoon Mangkhut was the equivalent of a Category 4 hurricane on the Saffir-Simpson Scale.

Typhoon Mangkhut intensified rapidly on Monday.  A circular eye was at the center of circulation.  A ring of strong thunderstorms surrounded the eye and the strongest winds were occurring in that ring of storms.  Several bands of showers and thunderstorms were revolving around the core of Typhoon Mangkhut.  Storms around the core were generating upper level divergence which was pumping mass away from the typhoon.

Winds to typhoon force extended out about 50 miles (80 km) from the center of circulation.  Winds to tropical storm force extended out about 210 miles (335 km) from the center.  The Hurricane Intensity Index (HII) for Typhoon Mangkhut was 28.2.  The Hurricane Size Index (HSI) was 18.9 and the Hurricane Wind Intensity Size Index (HWISI) was 47.1.

Typhoon Mangkhut will move through an environment capable of supporting very strong typhoons during the next two or three days.  Mangkhut will move over water where the Sea Surface Temperature is near 30°C.  It will move through a region where the upper level winds are weak and there will be little vertical wind shear.  Typhoon Mangkhut is likely to remain very strong for the next few days.  Eyewall replacement cycles could cause fluctuations in intensity.

Typhoon Mangkhut will move south of a ridge over the Western North Pacific Ocean.  The ridge will steer Mangkhut to the west during the next day or two.  Typhoon Mangkhut will move more toward the west-northwest later this week.  On its anticipated track Typhoon Mangkhut could be near northern Luzon in about four days.

Typhoon Mangkhut Brings Wind and Rain to the Marianas

Typhoon Mangkhut brought wind and rain to the Marianas on Sunday night.  At 11:00 p.m. EDT on Sunday the center of Typhoon Mangkhut was located at latitude 14.4°N and longitude 146.6°E which put it about 175 miles (285 km) east-northeast of Guam.  Mangkhut was moving toward the west at 19 m.p.h. (31 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 955 mb.  Typhoon Warnings were in effect for Saipan, Tinian, Rota and Guam.  The airport on Saipan was reporting sustained winds of 41 m.p.h. (66 km/h) and wind gusts to 61 m.p.h. (98 km/h).

Typhoon Mangkhut had a well organized circulation.  There was a circular eye at the center of Mangkhut.  A ring of strong thunderstorms surrounded the eye and the strongest winds were occurring in that ring of storms.  Several bands of showers and thunderstorms were revolving around the core of Typhoon Mangkhut.  Storms near the core were generating upper level divergence which was pumping mass away from the typhoon.

Winds to typhoon force extended out about 40 miles (65 km) from the center of circulation.  Winds to tropical storm force extended out about 150 miles (240 km) from the center.  The Hurricane Intensity Index (HII) for Typhoon Mangkhut was 13.9.  The Hurricane Size Index (HSI) was 13.5 and the Hurricane Wind Intensity Size Index was 27.4.  Typhoon Mangkhut was capable of causing regional significant damage.

Typhoon Mangkhut will move through an environment favorable for intensification.  Mangkhut will move over water where the Sea Surface Temperature is near 30°C.  An upper level ridge north of Mangkhut will cause easterly 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.  Typhoon Mangkhut could intensify into the equivalent of a major hurricane later this week.

The ridge north of Typhoon Mangkhut will steer the typhoon in a westerly direction.  The core of Typhoon Mangkhut will move over the Marianas during the next few hours.  It will bring strong winds and it will drop locally heavy rain.  On its anticipated track Typhoon Mangkhut could be east of Luzon later this week.

Hurricane Olivia Causes Tropical Storm Watches for Hawaii

The potential impacts of Hurricane Olivia caused the issuance of Tropical Storm Watches for Hawaii on Sunday night.  Tropical Storm Watches were issued for Oahu, Maui County including Maui, Molokai, Lanai, and Kahoolawe, and Hawaii County.  At 11:00 p.m. EDT on Sunday the center of Hurricane Olivia was located at latitude 21.4°N and longitude 146.1°W which put it about 595 miles (960 km) east-northeast of Hilo, Hawaii.  Olivia was moving toward the west 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 988 mb.

Hurricane Olivia maintained its intensity and structure on Sunday.  A circular eye persisted at the center of circulation and a ring of thunderstorms surrounded the eye.  The strongest winds were occurring in that ring of storms.  Several bands of showers and thunderstorms were revolving around the core of Hurricane Olivia.  Winds to hurricane force extended out about 25 miles (40 km) from the center of circulation.  Winds to tropical storm force extended out about 125 miles (200 km) from the center.

Hurricane Olivia will move through a less favorable environment during the next several days.  Olivia will move over water where the Sea Surface Temperature is near 26°C.  So, there will be enough energy in the upper ocean to support a hurricane.  However, an upper level trough north of Hawaii will produce southwesterly winds which will blow toward the top of Hurricane Olivia.  Those winds will cause more vertical wind shear and Hurricane Olivia could weaken to a tropical storm as it approaches Hawaii.

Hurricane Olivia will move south of a subtropical high pressure system over the Central Pacific Ocean.  The high is forecast to strengthen and it will steer Olivia on a west-southwesterly track.  On its anticipated track Olivia could approach Hawaii late on Tuesday.  Olivia will bring gusty winds and it could cause power outages.  Locally heavy rain and the potential for flash floods are greater risks.

Florence Strengthens Back Into a Hurricane

Florence strengthened back into a hurricane on Sunday morning.  At 11:00 a.m. EDT on Sunday the center of Hurricane Florence was located at latitude 24.4°N and longitude 56.3°W which put it about 750 miles (1210 km) southeast of Bermuda.  Florence was moving toward the west at 6 m.p.h. (10 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 984 mb.

Hurricane Florence was better organized on Sunday morning.  A NOAA research aircraft reported a circular eye with a diameter of 24 miles (39 km).  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 Florence.  Storms near the core were generating upper level divergence which was pumping mass away from the hurricane.  Winds to hurricane force extended out about 20 miles (35 km) to the east of the center of circulation.  Winds to tropical storm force extended out about 115 miles (185 km) to the north of the center and about 50 miles (80 km) to the south of the center.

Hurricane Florence will be moving through an environment favorable for intensification.  Florence 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 Florence will strengthen and it could intensify rapidly at times.  Florence is likely to be a major hurricane on Monday.

Hurricane Florence will move around the western end of a subtropical high pressure system over the western Atlantic Ocean.  The high will steer Florence in a general west-northwesterly direction.  On its anticipated track the center of Hurricane Florence will approach the southeast coast of the U.S. on Thursday.  It is likely to be a major hurricane at that time.

Elsewhere, Tropical Storm Helene and Tropical Storm Isaac moved westward over the tropical Atlantic Ocean.  At 11:00 a.m. EDT on Sunday the center of Tropical Storm Helene was located at latitude 13.2°N and longitude 25.0°W which put it about 120 miles (195 km) south-southwest of the Cabo Verde Islands.  Helene was moving toward the west at 13 m.p.h. (20 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 997 mb.  Tropical Storm Warnings were in effect for Santiago, Fogo and Brava.

At 11:00 a.m. EDT on Sunday the center of Tropical Storm Isaac was located at latitude 14.3°N and longitude 39.1°W which put it about 1470 miles (2370 km) east of the Windward Islands.  Isaac was moving toward the west at 9 m.p.h. (15 km/h).  The maximum sustained wind speed was 65 m.p.h. (105km/h) and there were wind gusts to 80 m.p.h. (130 km/h).  The minimum surface pressure was 999 mb.

Tropical Storm Florence Reorganizes Southeast of Bermuda

Tropical Storm Florence reorganized southeast of Bermuda on Saturday.  At 11:00 p.m. EDT on Saturday the center of Tropical Storm Florence was located at latitude 24.6°N and longitude 55.2°W which put it about 790 miles (1270 km) southeast of Bermuda.  Florence was moving toward the west at 6 m.p.h. (10 km/h).  The maximum sustained wind speed was 70 m.p.h. (110 km/h) and there were wind gusts to 85 m.p.h. (135 km/h).  The minimum surface pressure was 989 mb.

Vertical wind shear decreased around Tropical Storm Florence and the circulation showed evidence of better organization.  Stronger thunderstorms developed near the center of circulation and a primary rainband wrapped about three quarters of the way around the center.  An eye appeared to be forming.  Thunderstorms near the center generated more upper level divergence which pumped away mass and the surface pressure decreased on Saturday.  More thunderstorms also developed in other rainbands that were revolving around the core of the circulation.  Tropical Storm Florence appeared to be on the threshold of regaining hurricane intensity.

Tropical Storm Florence will be moving through an environment favorable for intensification during the next two or three days.  Florence will move over water where the Sea Surface Temperature is near 29°C.  It will move into a region where the upper level winds are weaker and there will be less vertical wind shear.  Tropical Storm Florence will intensify back into a hurricane on Sunday.  It could intensify rapidly once a eye and complete eyewall form.  Florence is likely to become a major hurricane by early next week.

Tropical Storm Florence will move near the western end of a subtropical high pressure system over the western Atlantic Ocean.  The high will steer Florence in a general west-northwesterly direction during the next few days.  On its anticipated track Florence could approach the southeast coast of the U.S. by Thursday.  It is likely to be a major hurricane at that time.  The steering currents could weaken when Florence approaches the U.S. and it is too early to make a precise forecast of landfall.

Elsewhere, Tropical Storms Helene and Isaac strengthened over the eastern tropical Atlantic Ocean.  At 11:00 p.m. EDT on Saturday the center of Tropical Storm Helene was located at latitude 13.2°N and longitude 22.8°W which put it about 155 miles (250 km) southeast of the Cabo Verde Islands.  Helene was moving toward the west 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. (120km/h).  The minimum surface pressure was 999 mb.  Tropical Storm Warnings were in effect for Santiago, Fogo and Brava.

At 11:00 p.m. EDT the center of Tropical Storm Isaac was located at latitude 14.4°N and longitude 37.5°W which put it about 1580 miles (2540 km) east of the Windward Islands.  Isaac was moving toward the west at 8 m.p.h. (13 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 1002 mb.

Tropical Storm Mangkhut Causes Typhoon Watch for Marianas

Tropical Storm Mangkhut caused a Typhoon Watch to be issued for the Marianas on Saturday.  A Typhoon Watch was in effect for Guam, Rota, Saipan and Tinian.  At 5:00 p.m. EDT on Saturday the center of Tropical Storm Mangkhut was located at latitude 14.9°N and longitude 156.0°E which put it about 760 miles (1225 km) east of Guam.  Mangkhut was moving toward the west at 24 m.p.h. (39 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 983 mb.

The circulation of Tropical Storm Mangkhut became much better organized on Saturday despite its rapid westward movement.  A primary band of thunderstorms wrapped around the southern side of the center of circulation and an eye appeared to be forming.  Winds near the core of Mangkhut were generating upper level divergence which was pumping mass away from the tropical storm.  Several other bands of showers and thunderstorms were revolving around the core of Tropical Storm Mangkhut.  The strongest rainbands were in the western half of the circulation.  Bands in the eastern half of the tropical storm consisted primarily of showers and lower clouds.  An upper level ridge north of Mangkhut was producing easterly winds which were blowing toward the top of the circulation.  Those winds were causing vertical wind shear and they were probably the reason why the strongest rainbands were west of the center of circulation.

Tropical Storm Mangkhut will move through an environment favorable for intensification.  Mangkhut will move over water where the Sea Surface Temperature is near 30°C.  It will move into an area where the upper level winds are weaker and there will be less vertical wind shear.  Tropical Storm Mangkhut will intensify into a typhoon on Sunday and it could intensify rapidly once the inner core and eye are fully formed.

Tropical Storm Mangkhut will move south of a ridge over the Western North Pacific Ocean.  The ridge will steer Mangkhut in a general westerly direction during the next few days.  On its anticipated track Tropical Storm Mangkhut could reach the Marianas in about 36 hours.  It is likely to be a typhoon at that time.  Mangkhut could bring strong winds and locally heavy rain to Guam, Rota, Saipan and Tinian.

Hurricane Olivia Churns Toward Hawaii

Hurricane Olivia churned toward Hawaii on Saturday.  At 11:00 a.m. EDT on Saturday the center of Hurricane Olivia was located at latitude 21.4°N and longitude 138.0°W which put it about 1110 miles (1790 km) east of Hilo, Hawaii.  Olivia was moving toward the west at 15 m.p.h. (24 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 Olivia weakened slowly on Saturday, but it still had a well organized circulation.  There was a circular eye at the center of circulation.  Several bands of showers and thunderstorms were revolving around the core of Hurricane Olivia.  The rainbands in the eastern half of the circulation were stronger than the bands in the western half of the circulation.  Storms near the core of Olivia were generating upper level divergence.

Hurricane Olivia will move through an environment that could allow it to remain a hurricane for several more days.  Olivia is currently over water where the Sea Surface Temperature is near 25°C, but it will move over slightly warmer water during the next several days.  An upper level trough north of Hawaii will produce southwesterly winds which will blow toward the top of the circulation.  Those winds will cause moderate vertical wind shear and they could cause Hurricane Olivia to weaken to a tropical storm early next week.

Hurricane Olivia will move south of a subtropical high over the Eastern North Pacific Ocean.  The high will steer Olivia toward the west during the next day or two.  The ridge is forecast to strengthen early next week and it will steer Olivia more toward the west-southwest.  On its anticipated track Hurricane Olivia could approach Hawaii on Tuesday night.

Elsewhere, Tropical Storm Norman moved north of Hawaii and weakened, while Tropical Depression Eighteen-E developed southwest of Baja California.  At 11:00 a.m. EDT on Saturday the center of Tropical Storm Norman was located at latitude 26.0°N and longitude 154.4°W which put it about 395 miles (630 km) northeast of Honolulu, Hawaii. Norman was moving toward the northwest at 9 m.p.h. (15 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 998 mb.

At 11:00 a.m. EDT on Saturday the center of Tropical Depression Eighteen-E was located at latitude 16.1°N and longitude 115.9°W which put it about 610 miles (980 km) southwest of the southern tip of Baja California.  It was moving toward the west-northwest at 12 m.p.h. (19 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 Mangkhut Develops Eastof the Marianas

Tropical Storm Mangkhut developed east of the Marianas on Friday.  At 5:00 p.m. EDT on Friday the center of Tropical Storm Mangkhut was located at latitude 13.1°N and longitude 163.2°E which put it about 1275 miles (2060 km) east of Guam.  Mangkhut was moving toward the west at 17 m.p.h. (28 km/h).  The maximum sustained wind speed was 40 m.p.h. (65 km/h) and three were wind gusts to 50 m.p.h. (80 km/h).  The minimum surface pressure was 998 mb.

A distinct center of circulation formed in a cluster of thunderstorms east of the Marianas and the Japan Meteorological Agency designated the system as Tropical Storm Mangkhut.  The circulation of Mangkhut was still organizing.  Bands of showers and thunderstorms were developing around Tropical Storm Mangkhut.  There were more thunderstorms on the western side of the circulation.  An upper level ridge north of Mangkhut was producing easterly winds which were blowing toward the top of the circulation.  Those winds were probably the reason why more of the thunderstorms were west of the center of circulation.

Tropical Storm Mangkhut will be moving through an environment favorable for intensification.  Mangkhut will move over water where the Sea Surface Temperature is near 30°C.  It will move south of the upper level ridge, which will cause some vertical wind shear.  However, the shear is not likely to be strong enough to prevent intensification.  Tropical Storm Mangkhut could strengthen into a typhoon by the end of the weekend.

Tropical Storm Mangkhut will move south of a subtropical ridge over the Western North Pacific Ocean.  The ridge will steer Mangkhut in a general westerly direction.  On its anticipated track Mangkhut could approach the Marianas in about 72 hours.  It is likely to be a typhoon at that time.

Florence Weakens to a Tropical Storm

Former Hurricane Florence weakened to a tropical storm on Thursday.  At 11:00 p.m. EDT on Thursday the center of Tropical Storm Florence was located at latitude 25.1°N and longitude 49.8°W which put it about 1035 miles (1665 km) east-southeast of Bermuda.  Florence was moving toward the west-northwest at 7 m.p.h. (11 km/h).  The maximum sustained wind speed was 70 m.p.h. (110 km/h) and there were wind gusts to 85 m.p.h. (135 km/h).  The minimum surface pressure was 993 mb.

An upper level trough west of former Hurricane Florence produced strong southwesterly winds which blew across the top of the circulation.  Those winds caused strong vertical wind shear and Florence weakened into a tropical storm.  Thunderstorms dissipated in rainbands in the western half of the tropical storm.  The ring of thunderstorms around the eye weakened and the western side of the eyewall was disrupted.  However, a distinct low level center of circulation persisted.  Thunderstorms northeast of the center still generated upper level divergence which pumped mass away to the northeast.

Tropical Storm Florence could weaken further on Friday because it will still be in the area of strong vertical wind shear.  However, as long as the lower part of the circulation remains intact, Tropical Storm Florence will be likely to strengthen during the weekend.  Florence is currently over water where the Sea Surface Temperature is near 28°C.  It will move over even warmer water during the weekend.  When Florence moves farther west, it will move into an area where the upper level winds are weaker and the wind shear will decrease.  Tropical Storm Florence is likely to intensify back into a hurricane during the weekend.

Tropical Storm Florence will move south of the subtropical high over the Atlantic Ocean.  The high will steer Florence in a generally west-northwesterly direction.  On its anticipated track, Florence could be southeast of Bermuda by Monday.  Florence could approach the east coast of the U.S. later next week.

Hurricanes Norma and Olivia Continue Westward

Hurricanes Norman and Olivia continued to move westward across the Pacific Ocean on Wednesday.  At 5:00 p.m. EDT on Wednesday the center of Hurricane Norman was located at latitude 19.9°N and 148.4°W which put it about 435 miles (700 km) east of Hilo, Hawaii. Norman was moving toward the west at 8 m.p.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 962 mb.

At 5:00 p.m. EDT on Wednesday the center of Hurricane Olivia was located at latitude 17.3°N and longitude 123.5°W which put it about 960 miles (1550 km) west-southwest of the southern tip of Baja California.  Olivia was moving toward the west-northwest at 13 m.p.h. (20 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 974 mb.

Although Hurricane Norman was in seemingly a less favorable environment, it intensified on Wednesday while Hurricane Olivia weakened.  The eye of Hurricane Norman became more distinct and it strengthened back to major hurricane status.  Hurricane Olivia weakened to Category 2 on the Saffir-Simpson Scale.  Both hurricanes were similar in size.  Winds to hurricane force extended out about 30 miles (50 km) from the center of Hurricane Norman and about 25 miles (40 km) from the center of Hurricane Olivia.  Winds to tropical storm force extended out about 115 miles (185 km) from the centers of both Hurricane Norman and Hurricane Olivia.

Both hurricanes are forecast to weaken gradually during the next several days.  Hurricane Norman will move over water cooler than 26.5°C.  An upper level trough will produce westerly winds which will blow toward the top of the circulation and cause more vertical wind shear.  The combination of cooler water and more shear will cause Hurricane Norman to weaken. Hurricane Olivia is currently over water where the Sea Surface Temperature is near 28°C, but it too will move over cooler water.  An upper level ridge north of Olivia will produce northwesterly winds which will cause more vertical wind shear.  Hurricane Olivia is also forecast to weaken during the next several days.

The upper level trough is forecast to turn Hurricane Norman toward the northwest on Thursday.  On its anticipated track Hurricane Norman will pass north of the Hawaiian Islands.  The ridge north of Hurricane Olivia is forecast to steer Olivia in a general westerly direction for another four or five days.  On its anticipated track Hurricane Olivia could be east of Hawaii by the end of the weekend.