Santa Ana winds fan damaging Califonia fire; Bahamas disturbance 95L fizzles

A small area of surface low pressure (95L) is about 200 miles north of Puerto Rico, and is headed west at 10-15 mph. The disturbance has lost most of its heavy thunderstorm activity over the past 12 hours, thanks to an intrusion of dry air. There is a moderate level of wind shear (15-20 knots) over 95L, but this morning's QuikSCAT pass showed no evidence of a surface circulation, and only a slight wind shift.

Wind shear is forecast to remain in the moderate range, 15-20 knots, over the next two days, as the disturbance heads west. Since water temperatures are a warm 28°C, this may allow some slow development, if the disturbance can avoid ingesting more dry air. Dry air is plentiful on 95L's west side. The disturbance may bring heavy rain to the Bahamas Friday night through Saturday night, but this is not guaranteed, due to the large amount of dry air the storm must overcome. By Saturday afternoon, as 95L approaches the central Bahamas, an approaching trough of low pressure should turn the disturbance sharply northward and northeastward. I'm not expecting 95L to affect Florida's weather this weekend. The National Hurricane Center is giving 95L a low (<20% chance) of developing into a tropical depression by Sunday morning. High wind shear should tear the disturbance apart on Sunday.


Figure 1.Latest satellite image of disturbance 95L.

Southern California Santa Ana winds fan damaging fire
A moderate to strong Santa Ana wind event began last night in Southern California, and will continue through Saturday night. Wind gusts up to 72 mph were clocked this morning in Montecito Hills in Santa Barbara County, fanning a fire that destroyed 80 homes and injured four people. A Fire Weather Warning has been posted for the Los Angeles area, and high wind warnings for winds of 25 to 45 mph with gusts to 65 mph have been posted for surrounding mountain areas. A strong high pressure system has built in to the north and east, and the clockwise flow of air around this high pressure system will drive strong east-to-west offshore winds from the mountains to the ocean over the Los Angeles and San Diego metropolitan areas through Saturday. As air drops out of the mountains, it will warm due to compression as its pressure increases, leading to very warm temperatures 10-20 degrees above average. Adding to the fire danger will be the very low humidities of this desert air, in the 15-25% range. Fire conditions will ease on Sunday as high pressure weakens, allowing winds to slow down and eventually shift so that they blow moisture from the ocean over Southern California.

I'll have an update this weekend if conditions warrant. Upcoming blogs for next week include a quick summary of this year's hurricane season, a look at the 212 mph wind gust recorded on Cuba during Hurricane Gustav, and the forecast for the upcoming winter.

Jeff Masters