Monthly Archives: August 2015

Guillermo Weakens, Tropical Storm Watch Issued for Hawaii

Guillermo weakened below hurricane intensity on Monday and the Central Pacific Hurricane Center issued a Tropical Storm Watch for some of the Hawaiian Islands.  At 11:00 p.m. EDT on Monday the center of Tropical Storm Guillermo was located at latitude 18.1°N and longitude 147.4°W which put it about 515 miles (830 km) east of Hilo, Hawaii.  Guillermo was moving toward the northwest at 10 m.p.h. (16 km/h).  The maximum sustained wind speed was 65 m.p.h. (100 km/h) and there were gusts to 75 m.p.h. (120 km/h).  The minimum surface pressure was 991 mb.  A Tropical Storm Watch has been issued for Hawaii County and Maui County including the islands of Maui, Molokai, Lanai and Kahoolawe.

An upper level trough north of Guillermo is causing strong southwesterly winds over the top of the circulation.  Significant vertical wind shear is affecting the tropical storm and is weakening it.  The southwesterly winds are also inhibiting upper level divergence on the western side of the storm.  Most of the thunderstorms are occurring in rainbands east of the center of circulation.  The vertical wind shear is expected to increase later this week and Guillermo will be moving over cooler Sea Surface Temperatures.  The weakening trend is expected to continue.

A subtropical ridge is pushing Guillermo toward the west-northwest and the southwesterly winds in the upper levels are turning it more toward the northwest.  That general motion is expected to continue for the next day or two.  On its anticipated track Guillermo is expected to pass north of Hawaii.  However, if it weakens a little faster than expected and the circulation is not as tall, then it could be steered by winds lower in the atmosphere.  Those winds could steer it more toward the west which would bring it nearer to Hawaii.  That possibility prompted the issuance of a Tropical Storm Watch for some of the Hawaiian Islands.

Typhoon Soudelor Becomes Equivalent of a Category 5 Hurricane

Typhoon Soudelor continued to intensify rapidly on Monday and it reached the equivalent of a Category 5 Hurricane on the Saffir-Simpson Scale.  At 5:00 p.m. EDT on Monday the center of Typhoon Soudelor was located at latitude 18.0°N and longitude 140.1°E which put it about 1020 miles (1640 km) east-southeast of Okinawa.  Soudelor was moving toward the west-northwest at 13 m.p.h. (21 km/h).  The maximum sustained wind speed was 175 m.p.h. (280 km/h) and there were wind gusts to 215 m.p.h. (350 km/h).  The minimum surface pressure was 907 mb.  The Hurricane Intensity Index (HII) for Soudelor was 40.4, the Hurricane Size Index was 13.6 and the Hurricane Wind Intensity Size Index was 54.0.  These indices mean that Soudelor is capable of producing regional catastrophic damage.

The upper level winds around Soudelor are very light and there is almost no vertical wind shear.  The typhoon has strong upper level divergence in all directions which is pumping out mass and causing the surface pressure to decrease rapidly.  It is over water where the Sea Surface Temperature is near 31°C and the circulation is extracting plenty of energy from the upper ocean.  The environment would support further intensification, but Soudelor is already a very powerful typhoon.  Soudelor rapidly completed an eyewall replacement cycle earlier today and future cycles could produce fluctuations in intensity.  Soudelor could remain a very intense typhoon for several more days.

A strong subtropical ridge is steering Typhoon Soudelor toward the west-northwest and that general steering pattern is expected to continue for the next few days.  On its anticipated track Soudelor could be near the southernmost islands of Japan in three days, near northern Taiwan in four days and near the coast of China in less than five days.  Although it is likely to weaken before it reaches any of those locations, it could still be a powerful typhoon at that time.

Hurricane Guillermo Weakening As It Moves Toward Hawaii

A reconnaissance aircraft confirmed a weakening trend in Hurricane Guillermo that had been suggested by satellite imagery.  At 11:00 p.m. EDT on Sunday the center of Hurricane Guillermo was located at latitude 15.5°N and longitude 145.0°W which put it about 725 miles (1165 km) east-southeast of Hilo, Hawaii.  Guillermo was moving toward the west-northwest at 10 m.p.h. (16 km/h).  The maximum sustained wind speed was 85 m.p.h. (145 km/h) and there were wind gusts to 100 m.p.h. (160 km/h).  The minimum surface pressure was 981 mb.

An upper level trough north of Guillermo is producing southwesterly winds over the top of the circulation.  Those winds are causing vertical wind shear and are inhibiting the upper level divergence on the western side of the circulation.  In addition Guillermo is gradually moving over cooler Sea Surface Temperatures (SSTs).  A combination of wind shear and cooler SSTs will continue to weaken the hurricane.

A subtropical ridge is steering Guillermo toward the west-northwest and that general motion is expected to continue.  On its anticipated track Guillermo would approach the Big Island of Hawaii in about 72 hours.  It will likely be a tropical storm at that time.

Typhoon Soudelor Intensifies Rapidly and Moves Over Saipan

Typhoon Soudelor intensified rapidly during the 12 hours before it moved directly over Saipan.  At 11:00 a.m. EDT on Sunday the center of Typhoon Soudelor was located at latitude 15.3°N and longitude 145.3°E which put it about 25 miles (40 km) west-northwest of Saipan.  It was moving toward the west-northwest at 11 m.p.h. (18 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. (205 km/h).  The minimum surface pressure was 956 mb.  The airport on Saipan measured sustained wind to 54 m.p.h. (87 km/h) and wind gusts to 91 m.p.h. (147 km/h).  However, there were several observations when no wind speed was reported.  The minimum surface pressure reported was 958 mb.

Typhoon Soudelor organized quickly after the primary band wrapped completely around the center of circulation.  A tiny (4 mile wide) pinhole eye developed at the center of circulation and there are multiple bands of thunderstorms rotating around the center.   Soudelor is over warm Sea Surface Temperatures and there is little vertical wind shear.  Further intensification is likely and Soudelor could reach Super Typhoon status.

A subtropical ridge is steering Soudelor toward the west-northwest and that general motion is expected to continue for the next few days.  On its anticipated track Soudelor could approach the southernmost islands of Japan or Taiwan in four or five days.

Hurricane Guillermo Crosses Into the Central Pacific

Hurricane Guillermo moved west of longitude 140°W on Saturday, which means it officially crossed into the Central Pacific Ocean.  The responsibility for issuing advisories on Guillermo shifted from the National Hurricane Center in Miami, Florida to the Central Pacific Hurricane Center in Honolulu, Hawaii when Guillermo moved west of 140°W.  At 11:00 p.m. EDT on Saturday the center of Hurricane Guillermo was located at latitude 14.0°N and longitude 141.0°W which put it about 1010 miles (1625 km) east-southeast Hilo, Hawaii.  Guillermo was moving toward the west-northwest at 12 m.p.h. (19 km/h).  The maximum sustained wind speed was 105 m.p.h. (165 km/h) and there were gusts to 125 m.p.h. (205 km/h).  The minimum surface pressure was 970 mb.

The structure of Hurricane Guillermo appeared to become less organized on Saturday.  There are fewer thunderstorms and the spiral bands appear to be weaker.  Guillermo is nearing water where the Sea Surface Temperature is near 27°C, and it will gradually move over even cooler water.  Westerly winds in the upper levels appear to be generating some vertical wind shear over the northern portion of the circulation.  Guillermo is still producing upper level divergence near the center of circulation, but the divergence appears to less over the western half of the hurricane.  The circulation may be pulling some drier more stable air into the western part of the circulation.  Guillermo will be moving into a less favorable environment and weakening is likely.

A subtropical ridge is steering Guillermo toward the west-northwest and that general motion is expected to continue during the next several days.  On its anticipated track Guillermo could approach the Big Island of Hawaii in about four days.  It is likely to be a tropical storm at that time.

Soudelor Almost a Typhoon as It Nears the Marianas

Tropical Storm Soudelor intensified on Saturday and it has almost reached typhoon status.  At 11:00 p.m. EDT on Saturday the center of Tropical Storm Soudelor was located at latitude 14.8°N and longitude 147.7°E which put it about 170 miles (275 km) east-southeast of Saipan.  Soudelor was moving toward the west-northwest at 18 m.p.h. (29 km/h).  The maximum sustained wind speed was 70 m.p.h. (115 km/h) and there were gusts to 85 m.p.h. (135 km/h).  The minimum surface pressure was 978 mb.  A Typhoon Warning has been issued for Saipan and Tinian.  A Tropical Storm Warning has been issued for Rota.  A Typhoon Watch has been issued for Agrihan, Pagan and Alamagan.

The structure of Tropical Storm Soudelor improved on Saturday.  A long spiral band wrapped almost entirely around the center of circulation and numerous other spiral bands were apparent on satellite imagery.  There are more thunderstorms on the western side of the circulation.  Soudelor is moving over water where the Sea Surface Temperature is near 30°C.  An upper level ridge north of the tropical storm is causing light easterly winds over the circulation.  However, the vertical wind shear is modest and upper level divergence is increasing.  Soudelor is in a favorable environment.  Further intensification is likely and rapid intensification is possible.  Soudelor will very likely be a typhoon when it moves through Marianas.

A subtropical ridge is steering Soudelor toward the west-northwest and that pattern is expected to continue during the next few days.  On its anticipated track Soudelor will be near Saipan and Tinian in about 12 hours.  It could bring strong winds to those locations and other nearby islands.