Nadine goes extratropical; the Atlantic is quiet

For the first day since August 20, the National Hurricane Center is not issuing advisories on an active tropical cyclone in the Atlantic. On Friday, Tropical Storm Nadine finally transitioned to an extratropical storm, due to cool waters and the influence of an upper-level low. The final fate of Nadine is very uncertain; the extratropical version of Nadine is expected to meander between the Azores Islands and Europe for at least a week, and could potentially become a tropical storm again. In their 8 am EDT Tropical Weather Outlook, NHC gave the ex-Nadine a 40% chance of becoming a subtropical or tropical cyclone by Monday morning.

We've been in a relatively quiet period in the Atlantic for over a week now, and the computer models predict that this quiet period will last at least another week. The quiet period is primarily due to the fact that the African Monsoon has been less active, and there are fewer tropical waves coming off the coast of Africa. Even the busiest hurricane season has quiet periods like this, and we should not assume that hurricane season is over. The first two weeks of October are typically a busy period for tropical cyclones in the Atlantic, and I expect that we'll see one or two more names storms in the Atlantic before October 15.


Figure 1. True-color MODIS satellite image of Ex-Tropical Storm Nadine, taken at 9:05 am EDT Saturday, September 22, 2012. Image credit: NASA.

Tropical Storm Jelawat a threat to the Philippine Islands
In the Western Pacific, Tropical Storm Jelawat threatens to become the most dangerous typhoon of the year for the Philippine Islands. Jelawat is located about 200 miles to the east of the islands, and is expected to move slowly to the northwest, roughly parallel to the Philippines, through Tuesday. Wind shear is moderate 5 - 15 knots, and Jelawat is over very warm ocean waters of 29°C. These warm waters extend to great depth, resulting in a total ocean heat content of over 100 KJ/cm^2, which is exceptionally high. These favorable conditions for intensification have prompted the Joint Typhoon Warning Center to predict that Jelawat will become a Category 4 typhoon by Tuesday. Satellite loops show that Jelawat is becoming more organized, with a large symmetric area of heavy thunderstorms with cold cloud tops. The long-range path of Jelawat is very uncertain; the 00Z ECMWF model takes the storm over the northern end of Luzon Island in the Philippines on Wednesday, while the latest 12Z run of the GFS model keep the storm several hundred miles east of the Philippines through Wednesday.


Figure 2. IR satellite image of Jelawat taken at 12:30 pm EDT Saturday, September 22, 2012.

I'll have a new post on Monday at the latest. Happy first day of fall!

Jeff Masters