September the globe's 8th warmest on record; heavy rains hit Florida

September 2011 was the globe's 8th warmest September on record, according to the National Oceanic and Atmospheric Administration (NOAA) National Climatic Data Center (NCDC). NASA's Goddard Institute for Space Studies rated September the 9th warmest on record. NASA rates the top ten warmest Septembers since 1880 as having all occurred in the past ten years. September 2011 global land temperatures were the 4th warmest on record, and ocean temperatures were the 14th warmest on record for the month of September. Global satellite-measured temperatures for the lowest 8 km of the atmosphere were above average, the 8th or 5th warmest in the 34-year record, according to Remote Sensing Systems and the University of Alabama Huntsville (UAH).


Figure 1. Departure of temperature from average for September 2011. Image credit: National Climatic Data Center (NCDC).

21st warmest September for the U.S.
September 2011 in the U.S. was the 21st warmest in the 117-year period of record, according to the National Climatic Data Center. Thirteen states in the West and Northeast had top-ten warmest Septembers on record, and one state, Mississippi, had a top-ten coolest September. On September 4th, Tropical Storm Lee made landfall on the Gulf Coast, and brought torrential rain to most of the eastern United States. While Lee brought drought relief for the Gulf Coast, it caused major flooding in the already-saturated Northeast. Rainfall totals of at least 10 inches were common along Lee's path. Eleven states from Louisiana to New York experienced a top-ten wettest September, and it was the wettest September in Pennsylvania's history. In Binghamton, New York, Lee aided in breaking three all-time precipitation records: most rainfall in a year (57.85 inches to date), most rainfall in any month (16.58 inches), and most rainfall on any calendar day (7.49 inches on September 7th). Dayton, Ohio and Allentown, Pennsylvania both had their wettest September on record. In contrast, five states had a top-ten driest September. Ten percent of the United States was in an exceptional drought--the most extreme classification--in September. Austin, Texas saw its driest September on record, receiving only 0.01 inches of rain during the month.

Weak La Niña conditions continue
La Niña continues in the equatorial Pacific, where sea surface temperatures remain 0.5°C to 1.0°C below average, qualifying this as a weak La Niña event. During the coming winter, La Niña is likely to bring drought in the South, especially to Texas. Above average temperatures can also be expected in the South. The Pacific Northwest can expect cooler than average temperatures, as well as the potential for another record-breaking winter of snowpack across the western United States. La Niña also tends to bring wetter than average conditions to the Ohio Valley.

Arctic sea ice extent second lowest on record
Arctic sea ice extent was at its second lowest on record in September, behind 2007, according to the National Snow and Ice Data Center. The center said that on September 9th, the Arctic reached its annual minimum extent, which was also the second-smallest minimum extent on record. Sea ice records date back to 1979.

Wunderground's weather historian Christopher C. Burt has an in-depth analysis of some of the more notable September global extremes in h is latest post.


Figure 2. Radar-estimated rainfall for the 24 hours ending at 9:20 am EDT over South Florida. Heavy rains of up to 5 inches affected the coast near Naples and portions of the Keys.

Heavy rains continue over South Florida
Heavy rains continue over South Florida due to the lingering remnants of Invest 95L. Key West Naval Air Facility has picked up an additional 4.61" of rain as of 9 am EDT this morning, bringing their 5-day total to 17.42" of rain. Yesterday, 95L spawned three tornadoes over Southeast Florida. One twister damaged 40 homes near Lakeport, and roofs were torn off homes in Sunrise. No injuries were reported from the tornadoes. The severe threat shifts to coastal North Carolina today, and NOAA's Storm Prediction Center has placed much of coastal North Carolina and Virginia in their "slight risk" area for severe weather.

None of the computer models predicts tropical storm formation in the Atlantic during the coming seven days. The Western Caribbean is expected to see an increase in moisture late next week and the possible formation of a strong tropical disturbance capable of bringing heavy rains.

My next post will be early Thursday afternoon, after NOAA issues their winter outlook at 11 am EDT that day.

Jeff Masters and Angela Fritz