Quiet tropics; the globe experiences its 4th warmest September on record

It's a quiet Wednesday in the tropics. A weak low pressure system near Puerto Rico is kicking up some showers, but this system is under 30 knots of wind shear and is not expected to develop. Wind shear is expected to be relatively light across the Caribbean and southern Gulf of Mexico most of the coming week, and the NOGAPS model is forecasting that a tropical storm will form in the southern Caribbean on Saturday. The storm is forecast to move northwards, threatening Jamaica, the Cayman Islands, and Cuba early next week. None of the other models are picking up on this, and the NOGAPS has been wrong once before this month on a similar type of forecast. Residents of the Caribbean, south Florida, and the Bahamas should keep an eye on possible development later this week, but I doubt that we'll see a tropical storm in the Caribbean like the NOGAPS model is forecasting.

An unusually cool September in the U.S.
The U.S. experienced its first month with below normal temperatures in over two years last month, according to the National Climatic Data Center September summary. September 2006 was the 31st coolest September dating back to 1895, and the first month with below-normal temperatures since August 2004. Still, January to September was the warmest such year-to-date period on record in the U.S. The nationally averaged year-to-date temperature was 58.3�F (14.6�C), a full 1�F above the record set just last year in 2005. Interestingly, the United States was the only region of the globe that saw significantly cooler than normal temperatures in September (Figure 1). September 2006 was the 37th wettest September on record in the U.S., and Kentucky had its wettest September ever. The cool weather in the U.S. was due to a southward dip of the jet stream over the nation; this jet stream pattern also acted to steer September's hurricanes away from the U.S. and out to sea.


Figure 1. Temperature departure from normal for September 2006.

Globally, the 4th warmest September on record
While the U.S. cooled off in September, the rest of the globe stayed hot. September 2006 was the 4th warmest September globally since records began in 1880 (1.0�F/0.56�C above the 20th century mean). January to September 2006 was the 4th warmest such period on record. Global ocean temperatures for September were the 3rd warmest on record, thanks in part to an El Ni�o episode that began in September. Sea ice extent in the Arctic was the second lowest on record this September. The record low was set in 2005.

Jeff Masters