Monthly Archives: September 2017

Tropical Storm Mawar Nears Landfall in China

Tropical Storm Mawar moved closer to a landfall in China on Saturday.  At 11:00 p.m. EDT on Saturday the center of Tropical Storm Mawar was located at latitude 22.2°N and longitude 116.4°E which put it about 150 miles (240 km) east of Hong Kong.  Mawar was moving toward the west-northwest at 5 m.p.h. (8 km/h).  The maximum sustained wind speed was 55 m.p.h. (90 km/h) and there were wind gusts to 70 m.p.h. (110 km/h).  The minimum surface pressure was 989 mb.

The circulation of Tropical Storm Mawar is very asymmetrical.  Most of the thunderstorms are located south of the center of circulation.  A primary rainband is just south of the center of circulation and there are several other bands farther south of the center.  Recent visible satellite images suggest that the eastern end of the primary rainband could be trying to wrap around the center.  Thunderstorms in the primary rainband were generating some upper level divergence which was pumping mass away to the southwest of the tropical storm.

Tropical Storm Mawar will move through an environment that is somewhat favorable for intensification during the next 12 to 18 hours.  Mawar will move over water where the Sea Surface Temperature is near 29°C.  An upper level ridge centered over China is producing northeasterly winds which are blowing toward the top of the circulation.  Those winds are generating moderate vertical wind shear.  Those winds may also be the reason for the asymmetrical distribution of thunderstorms.  Mawar could intensify before it makes landfall in China.

Tropical Storm Mawar is being steered slowly toward the west-northwest by a ridge near Japan.  That general motion is expected to continue for the next several days.  On its anticipated track Tropical Storm Mawar will make landfall in China east of Hong Kong in 12 to 18 hours.  Mawar will bring gusty winds and locally heavy rain to parts of Guangdong province.  The rain could contribute to flooding in some locations.  Mawar is likely to weaken steadily after it makes landfall.

Tropical Storm Lidia Weakens, Still Raining on Baja California

Tropical Storm Lidia has weakened but it is producing rain over Baja California.  At 2:00 p.m. EDT on Saturday the center of Tropical Storm Lidia was located at latitude 28.3°N and longitude 114.6°W which put it about 40 miles (65 km) northeast of Punta Eugenia, Mexico.  Lidia was moving toward the northwest 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 999 mb.

A Tropical Storm Warning is in effect for the portion of the coast from Punta Abreojos to San Jose de Las Palomas, from Mulege to Isla San Luis and from Guaymas to Puerto Libertad, Mexico.

Tropical Storm Lidia weakened during the past 24 hours as it slowly moved northwest over Baja California.  There are some indications that the upper portion of the circulation may have decoupled from the lower half of Tropical Storm Lidia.  The upper portion of the circulation appears to be over the Gulf of California.  There are stronger thunderstorms over the Gulf of California because the Sea Surface Temperature is near 32°C in that body of water.  Those thunderstorms are producing heavy rain over parts of the eastern side of Baja California and the western part of Mexico adjacent to the Gulf of California.  The lower level center appears to be located northeast of Punta Eugenia over the Pacific Ocean just west of Baja California.  There are showers and thunderstorms near the low level center and they are dropping heavy rain in that area.  The potential for flash floods still exists in the areas where heavy rain is falling.

The low level center of Tropical Storm Lidia is forecast to continue to move toward the northwest.  Lidia will continue to weaken because the low level center is moving over water where the Sea Surface Temperature is near 23°C.  It will take several more days for the low level center to spin down and it could still produce locally heavy rain over the northern part of Baja California during that time.  The upper level portion of the circulation will likely be absorbed by the larger scale environmental flow in those levels.  Some clouds and moisture in the upper levels could flow over the southwestern U.S.

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.

Tropical Storm Lidia Brings Wind and Heavy Rain to Baja California

Tropical Storm Lidia brought gusty winds and very heavy rain to Baja California on Thursday night.  At 11:00 p.m. EDT on Thursday the center of Tropical Storm Lidia was located at latitude 23.3°N and longitude 110.4°W which put it about 40 miles (65 km) northwest of Cabo San Lucas, Mexico.  Lidia was moving toward the north-northwest at 4 m.p.h. (6 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 991 mb.

A Hurricane Watch was in effect for the portion of the coast from Puerto Cortes to La Paz, Mexico including Cabo San Lucas.  A Tropical Storm Warning was in effect for the portion of the coast from Punta Eugenia to Bahia San Juan Bautista including Cabo San Lucas and from Bahia Tempehuaya to Bahia Kino.  A Tropical Storm Watch was in effect for the portion of the coast from Punta Eugenia to San Juan de Las Palomas and from Bahia San Juan Bautista to Isla San Luis and from Bahia Kino to Puerto Libertad.

Tropical Storm Lidia intensified as it approached the southern tip of Baja California on Thursday.  Several bands of showers and thunderstorms wrapped around the center of circulation and a partial eyewall appeared to form.  The airport at Cabo San Lucas reported sustained winds of 58 m.p.h. (83 km/h) and a Mexican automated station reported a sustained wind of 70 m.p.h. (113 km/h) and gusts to 90 m.p.h. (145 km/h) at a height of 735 feet (244 meters).  Tropical Storm Lidia has a large circulation.  Winds to tropical storm force extend out about 185 miles (295 km) from the center of circulation.

The large size of Tropical Storm Lidia meant that it was bringing tropical storm winds to the southern part of Baja California and parts of the west coast of Mexico.  Lidia was also producing very heavy rain over Baja California.  Flash floods are likely in places where steep terrain causes water to run off quickly.

Tropical Storm Lidia is forecast to move slowly north-northwest over Baja California.  The slow motion will prolong the period of gusty winds.  It will also cause the rain totals to be higher and increase the risk for floods.  Much of the circulation will remain over water and the large size of Lidia will mean that the tropical storm will weaken slowly.