New disturbance affecting Lesser Antilles; Typhoon Xangsane batters the Philippines

A tropical wave moving through the northernmost Lesser Antilles Islands this morning has been declared "Invest 97L" by the National Hurricane Center. Although small, the wave has developed enough heavy thunderstorm activity to be of concern. The wave is moving west-northwest at 15 mph, and will bring heavy rains and gusty winds to Antigua, St. Maarten, and surrounding islands today, and Puerto Rico on Friday. Martinique radar shows a moderate area of heavy rain moving through the islands. Antigua has seen some heavy rain this morning and gusty winds. Winds shifted to southwesterly at 11am EDT this morning, indicating that a closed surface circulation may exist. QuikSCAT winds at 6:22am EDT this morning showed a large area of 20-25 mph winds under these thunderstorms, and a strong wind shift, but not a closed surface circulation. The wave is under about 10 knots of wind shear, and this shear is expected to remain below 15 knots the next two days. The low shear and warm waters the system is over may allow some continued development. The computer models are not tracking this system very well because it is so small, but it appears likely that the storm will pass just north of the Bahamas and then turn north. The storm will probably not hit the U.S. East Coast. The earliest this could become a tropical depression is Sunday.


Figure 1. Preliminary models tracks for Invest 97L.

Typhoon Xangsane
Typhoon Xangsane roared over the main Philippine Island of Luzon yesterday, passing directly over the capital city of Manila, home to 12 million people. Xangsane was rated as a Category 3 storm when it hit Manila, but winds of only Category 1 strength affected the city. The Manila airport recorded maximum sustained winds of 60 mph, gusting to 89 mph as the northern eyewall of Xangsane battered the city about noon local time. Manila passed into the calm of the eye, recording a pressure of 954 mb. Eleven deaths have been blamed on the typhoon so far, five of them from a mudslide in a mountainous area. Thirty people are missing in a dam collapse south of Manila. Xangsane's death toll is likely to go much higher when the area southeast of Manila where Xangsane made landfall as a Category 4 typhoon is heard from. Damage so far has been heavy, particularly to agriculture, and losses will likely reach several hundred million dollars. Xangsane did extensive damage to the power grid of Luzon, and the entire island experienced a blackout. Only 5% of the island has seen power restored thus far.

The last significant typhoon to affect Manila was 1995's Supertyphoon Angela, which killed 740, left 650,000 homeless, and caused severe damage to the agricultural areas surrounding the capital. Angela was one of 14 tropical storms or typhoons to affect the Philippines that year. So far this year, four typhoons have affected the Philippines. Interaction with land has weakened Xangsane on its passage over the Philippine Islands, but the typhoon should intensify once more this weekend into a major typhoon before hitting Vietnam on Sunday.


Figure 1. Typhoon Xangsane at landfall in the Philippines. Image credit: NASA.

Isaac is born
Tropical Storm Isaac formed over the waters southeast of Bermuda this morning. QuikSCAT wind data from 4:43am EDT this morning showed numerous wind barbs of tropical storm strength, which was given as the justification ofr upgrading the storm at 11am today. However, satellite imagery this morning shows a decrease in the amount and intensity of the thunderstorm activity near the center. Isaac is not a classic tropical storm, and may be more properly called a subtropical storm--one that is a hybrid between a true tropical storm and an extratropical storm. An upper level low is bringing about 10 knots of shear over the storm and some dry air into the center from the southwest. These negative influences are expected to decrease over the next 48 hours, which should allow slow intensification. All of the models predict that Isaac will turn north and recurve out to sea, and will not be a threat to any land areas.

Elsewhere in the tropics
The Western Caribbean near the Yucatan Peninsula could see some development early next week, when a strong cold front is expected to push off the East Coast of the U.S. and stall out over this region. The NOGAPS model continues to forecast tropical storm development here next week.

An area of heavy thunderstorms associated with a tropical wave near 9N 50W, about 500 miles east of the South American coast, is moving west at 15 mph. This wave is under about 10 knots of shear, but is disorganized, and I don't expect it to develop.

I'll have an update Friday morning.
Jeff Masters