September 2010: 4th or 8th warmest on record for the globe

September 2010 was the globe's eighth 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 2010 the fourth warmest September on record. Both NOAA and NASA rated the year-to-date period, January - September, as the warmest such period on record. September 2010 global ocean temperatures were the ninth warmest on record, and land temperatures were also the ninth warmest on record. Global satellite-measured temperatures for the lowest 8 km of the atmosphere were the warmest on record, according to both Remote Sensing Systems data and University of Alabama Huntsville data. The year-to-date period January-September is the 2nd warmest such period in the satellite data, behind 1998.

For those interested, NCDC has a page of notable weather highlights from September 2010.


Figure 1. Departure of temperature from average for September 2010. Image credit: National Climatic Data Center (NCDC).

Fourteenth warmest September on record for the U.S.
For the contiguous U.S., it was the 14th warmest September in the 116-year record, according to the National Climatic Data Center. The year-to-date period, January to September, was the 24th warmest such period on record. Ten states had a top-ten warmest September on record--Rhode Island, Maine, New Hampshire, Connecticut, Massachusetts, New Jersey, Florida, Colorado, New Mexico, and Arizona. No states recorded a top-ten coldest September.

U.S. precipitation near average
For the contiguous U.S., September 2010 ranked near average. However, there were large regional variations in precipitation. Wyoming had its driest September in the 116-year record, and three other states had top-ten driest Septembers--Louisiana, Mississippi, and Florida. Minnesota had its wettest September on record, and five other states had a top-ten wettest September--North Dakota, South Dakota, Washington, Wisconsin, and Missouri.

La Niña intensifies to the "strong" category
The equatorial Eastern Pacific Ocean is now experiencing strong La Niña conditions. Sea surface temperatures (SSTs) over the tropical Eastern Pacific in the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region", dropped to 1.8°C below average during the first two weeks of October, according to NOAA. The Australian Bureau of Meteorology put this number at 1.53°C below average (as of October 10.) Moderate La Niña conditions are defined as occurring when this number is 1.0°C - 1.5°C below average. Temperatures colder than 1.5°C below average qualify as strong La Niña conditions. NOAA is maintaining its La Niña advisory, and expects La Niña conditions to last through the coming winter into spring.

Both El Niño and La Niña events have major impacts on regional and global weather patterns. For the remainder of October, we can expect La Niña to bring cloudier and wetter than average conditions to the Caribbean, but weather patterns over North America should not see much impact. La Niña typically causes warm, dry winters over the southern portion of the U.S., with cooler and wetter than average conditions over the Pacific Northwest. The Ohio and Mississippi Valleys states typically have wetter winters than usual.

September 2010 Arctic sea ice extent 3rd lowest on record
Northern Hemisphere sea ice extent in September 2010 was the third lowest in the 31-year satellite record behind 2007 and 2008, according to the National Snow and Ice Data Center. Ice volume in September was the lowest on record, according to University of Washington Polar Ice Center. The reported volume of 1,000 cubic miles (4,000 cubic kilometers) was 70 percent below the 1979 - 2009 September average of 3,200 cubic miles (13,400 cubic kilometers). Sea ice volume accounts for sea ice extent as well as the thickness of ice beneath the ocean's surface. The Northwest Passage through the normally ice-choked waters of Canada, as well as the Northeast Passage along the coast of northern Russia, remained open for ice-free navigation for most of September, but are now frozen shut again. This is the third consecutive year--and third time in recorded history--that both passages have melted open. Mariners have been attempting to sail these passages since 1497, and 2005 was the first year either of these passages reported ice-free conditions; 2008 was the first year both passages melted free. The 2010 Arctic melt season allowed for two sailing expeditions--one Russian and one Norwegian--to successfully navigate both the Northeast Passage and the Northwest Passage in a single season, the first time this feat has occurred in modern history.

New Caribbean disturbance
Heavy thunderstorm activity is currently limited over the southern Caribbean waters just north of Panama, but the latest 2am EDT (6Z) NOGAPS and GFS model runs continue to predict the formation of a tropical depression in the region 3 - 5 days from now. The NOGAPS model predicts that the storm will move northwest towards the Cayman Islands, while the GFS model takes the storm west-northwest over Nicaragua and Honduras. NHC is giving the disturbance a 10% chance of developing into a tropical depression by Monday. Northeastern Nicaragua and Honduras can expect a period of very heavy rains from the disturbance Saturday night through Tuesday.


Figure 2. Visible satellite image of Megi at 3:30am EDT 10/16/10. Image credit: Navy Research Lab, Monterey.

Typhoon Megi
In the Western Pacific, Typhoon Megi has attained Category 3 strength, and is predicted to intensify into a 150 mph supertyphoon that will strike the northern Philippine Island of Luzon on Monday morning. If this forecast verifies, Megi would be the strongest tropical cyclone to strike land globally in 2010. The globe has had an unusually low number of landfalling major hurricanes this year. Only one Category 4 or stronger storm has hit land--Tropical Cyclone Tomas, which hit Fiji on March 15 as a Category 4 storm with 135 mph winds. Tomas killed 3 people and did $45 million in damage to Fiji, and was the strongest storm to hit Fiji since Cyclone Bebe in 1972. The only other major tropical cyclones in 2010 to make landfall were Tropical Cyclone Oli, which passed through French Polynesia on February 5 as a Category 3 storm; Tropical Cyclone Rene, which hit Tonga in the South Pacific as a Category 3 storm on February 15; Typhoon Fanapi, which hit Taiwan on September 19 as a Category 3 storm; and Hurricane Karl, which hit Mexico near Veracruz on September 17 as a Category 3 hurricane.

Next update
I'll have an update Sunday or Monday morning.

Jeff Masters