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Second warmest September on record for the globe

By: Dr. Jeff Masters, 12:49 PM GMT on October 16, 2009

The globe recorded its second warmest September since record keeping began in 1880, according to NOAA's National Climatic Data Center. The combined global land and ocean temperature anomaly was 0.62°C (1.12°F), falling only 0.04°C (0.07°F) short of tying the record set in 2005. NASA's Goddard Institute for Space Studies also rated September 2009 as the 2nd warmest September on record, falling 0.02°C short of the record set in 2005. It was the 33rd consecutive September with a global temperature above the 20th century average. NOAA rated the year-to-date period, January - September 2009, as the sixth warmest such period on record. The September satellite-measured temperatures for the lowest 8 km of the atmosphere were the 2nd warmest on record, behind 1998. Global ocean Sea Surface Temperature (SST) anomalies, however, cooled a bit, and were the 5th warmest on record. Global SSTs were the warmest on record during the Northern Hemisphere summer, June - August.

Figure 1. Departure of temperature from average for September 2009. Image credit: National Climatic Data Center.

A warm September for the U.S., and record heat in the West
For the contiguous U.S., the average September temperature was 1.0°F above average, making it the 32nd warmest September in the 115-year record, according to the National Climatic Data Center. The West had is warmest September on record, with Nevada and California recording their warmest September, and six other western states observing a top-ten warmest September--Montana (3rd warmest), North Dakota (3rd), Idaho (4th), Utah (5th), Minnesota (6th), and Oregon (8th). However, a combination a slow-moving storm system during the beginning of the month and two surface cold fronts during the last week resulted in much below normal temperature averages in Kansas (10th coolest) and Oklahoma (11th coolest). The year-to-date (January - September) period was the 29th warmest such period for the contiguous U.S.

U.S. precipitation near average
U.S. precipitation in September was exactly average. Statewide-averaged rainfall was among the ten wettest for four southern states (Arkansas, 2nd wettest; Tennessee (5th), Mississippi (6th), and Alabama (6th)). Maine and Wisconsin each experienced their fourth driest September and both New Hampshire and Michigan had their seventh driest such periods.

U.S. drought
At the end of September, 15% of the contiguous United States was in moderate-to-exceptional drought. This is a drop from the 19% figure observed at the beginning of the year. Exceptional drought (the worst category of drought) was seen in South to Central Texas, though the area covered by exceptional drought shrank by 50% over the past month, thanks to much-needed rains over the region.

U.S. fire activity
During September, 5,535 fires burned approximately 378,523 acres, each of which was below the 2000 - 2009 average for the month. The acreage lost to wildfire was roughly half of the 2000 - 2009 average. For the year to date (January.September), 70,217 fires was slightly above the 10-year average, while acreage burned was slightly less than average.

Weak El Niño conditions continue
El Niño conditions continue over the tropical Eastern Pacific. Ocean temperatures in the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region", were 0.3°C above the threshold for a weak El Niño, according to the Australian Bureau of Meteorology. NOAA's Climate Prediction Center is maintaining an El Niño Advisory. Current conditions and model forecasts favor the continued development of a weak-to-moderate strength El Niño event into the Northern Hemisphere Fall 2009, with the likelihood of at least a moderate strength El Niño (3-month Niño-3.4 SST index of +1.0°C or greater) during the Northern Hemisphere Winter 2009-10.

September sea ice extent in the Arctic 3rd lowest on record
September 2009 Northern Hemisphere sea ice extent was the 3rd lowest since satellite measurements began in 1979, according to the National Snow and Ice Data Center (NSIDC). Only 2007 and 2008 saw lower Arctic sea ice extent. Both the Northwest Passage and Northeast Passage melted free, according to the National Snow and Ice Data Center. This marks the second consecutive year--and the second time in recorded history--both of these Arctic shipping routes have melted free. The past five years have had the five lowest Arctic ice extents on record. In their 2009 report on this year's Arctic sea ice minimum, NSIDC Director and Senior Scientist Mark Serreze said, "It's nice to see a little recovery over the past couple years, but there's no reason to think that we're headed back to conditions seen back in the 1970s. We still expect to see ice-free summers sometime in the next few decades". Only 19% of the ice cover this summer in the Arctic was over 2 years old, the least in the satellite record, and far below the 1981 - 2000 average of 52%. NSIDC Scientist Walt Meier said, "We've preserved a fair amount of first-year ice and second-year ice after this summer compared to the past couple of years. If this ice remains in the Arctic through the winter, it will thicken, which gives some hope of stabilizing the ice cover over the next few years. However, the ice is still much younger and thinner than it was in the 1980s, leaving it vulnerable to melt during the summer". Earlier this summer, NASA researcher Ron Kwok and colleagues from the University of Washington in Seattle published satellite data showing that Arctic ice thickness declined by 0.68 meters (2.2 feet) between 2004 and 2008. The overall mean winter thickness was 3.64 meters in 1980, and 1.89 meters during the winter of 2007 - 2008, a massive decrease of 48%.

Kwok, R., and D. A. Rothrock. 2009. Decline in Arctic sea ice thickness from submarine and ICESat records: 1958.2008, Geophys. Res. Lett., 36, L15501, doi:10.1029/2009GL039035.

Figure 2. Category 1 Typhoon Lupit in the Philippine Sea at 04:45 UTC October 16, 2009. Image credit: NASA MODIS Rapid Response System.

Tropical update
In the Atlantic, there are no threat areas to discuss, and none of the computer models is calling for tropical storm formation over the next week.

There are two potential serious threats in the Pacific. Tropical Storm Rick off the Pacific coast of Mexico is expected to recurve to the north and threaten Baja late next week. While Rick is expected to become a major hurricane early next week, the storm should weaken significantly before any potential landfall in Mexico, due to high wind shear and cooler ocean temperatures the storm will find as it approaches Baja.

More seriously, Typhoon Lupit in the Western Pacific is expected to intensify into a Category 4 typhoon and threaten the northern Philippines by Tuesday. Last week, Super Typhoon Parma crossed over the northern Philippines three times, dumping over twenty inches of rain in many locations. Over 300 people died in the resulting flash floods and landslides. A visit by Typhoon Lupit could create a major catastrophe in the northern Philippines as the storm dumps another 1 - 2 feet of rain on the already saturated soils.

My next post will be Sunday or Monday.

Jeff Masters

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The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.