Florida's soaking continues; 5th warmest April for the globe

The large extratropical storm that has been drenching Florida over the past few days continues to pour rain on the state as it treks slowly westward over the Gulf of Mexico. Rainfall amounts as high as 13.3 inches have been measured in Northern Florida in Flagler County over the past three days, with another 2 - 4 inches expected from the storm. The storm is bringing beach erosion, 7 - 10 foot waves, and tides 2 - 3 feet above normal to the Northeast Florida coast, along with damaging thunderstorm winds. While the storm's center is located just offshore Southwest Florida, a large band of precipitation arcs to the north and east, extending over northern Florida. This type of structure is typical of subtropical storms, though the storm does not have enough heavy thunderstorm activity or warm core air to qualify as a subtropical storm. The storm is under about 30 knots of wind shear, and shows no signs of developing more tropical characteristics. The computer models generally predict the storm should weaken this week as it moves towards Louisiana or Texas. As the center moves farther north over the next few days, it will be moving into a region of lower wind shear, and I still give the storm a 20% chance of becoming a subtropical depression 2 - 7 days from now.


Figure 1. Latest satellite image of the Gulf of Mexico storm.

Fifth warmest April on record
The globe recorded its 5th warmest April on record, according to the National Climatic Data Center. The period January - April was tied for the sixth warmest such period on record. April marked the first time since October 2008 that the planet has recorded a monthly temperature anomaly in the top five warmest months. The warming may be due to the fact that a La Niña event ended in the Eastern Pacific in April. Global temperature records go back to 1880.

A cool, wet April for the U.S.
For the contiguous U.S., April temperatures were the 36th coolest in the 115-year record, according to the National Climatic Data Center. The month was also quite wet, ranking as the 35th wettest April. The warmest state was New Hampshire, which recorded its 8th warmest April. The coldest state was South Dakota, which wad its 25th coldest April. Through April, U.S. tornado activity was very close to the mean observed during the past five years, according to NOAA's Storm Prediction Center. However, there were just 15 tornado deaths through April, compared to 70 deaths through April of 2008, and the 3-year average of 60 deaths.

On May 12, 2009, 17% 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. However, The amount of the U.S. in the highest levels of drought, extreme to exceptional, had increased from 1.2% at the beginning of the year to 2.6% by May 12. These extreme drought regions were in South Texas and South Florida.

La Niña officially over
The La Niña event of September 2008 - March 2009 is officially over, according to NOAA's Climate Prediction Center. They define La Niña conditions as occurring when the 1-month mean temperature anomaly in the equatorial Eastern Pacific (the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region") cools below -0.5°C and is expected to persist for three consecutive months. Temperatures warmed significantly in the Equatorial Eastern Pacific during April, and are now near average in the Niña 3.4 region. Most of the model forecasts for the Niño 3.4 region predict neutral conditions for the August - October peak of hurricane season. Three out of 16 El Niño models are predicting an El Niño event for hurricane season. Columbia University's International Research Institute for Climate and Society (IRI) is predicting a 30% chance of an El Niño event during the coming hurricane season. The number of Atlantic hurricanes is typically reduced in an El Niño year, due to increased wind shear from strong high-level winds.

Sea ice in the Arctic below average, but not greatly so
April 2009 Northern Hemisphere sea ice extent was the 10th lowest since 1979, according to the National Snow and Ice Data Center. The record April low was set in 2007. The rate of ice decline in April was the third slowest on record, thanks to cooler than usual temperatures over the Arctic. Nevertheless, the Arctic remains vulnerable to near-record melting this summer if much warmer than average temperatures return to the region. Strong winter winds pushed a considerable amount of multi-year-old ice out of the Arctic this year, leaving the Arctic with the lowest amount of old sea ice on record in March. The amount of ice more than two years old fell below 10% for the first time since satellites began observing the ice in 1979.

Jeff Masters