Pacific Equatorial sea surface temperatures cooled dramatically during the past three months and La Nina conditions are now firmly established, according to a University of Nebraska report. The extent of the cold pool now encompasses the region from South America westward through the dateline with the depth of the cold pool extending over 200 meters in the central Pacific. Numerical models indicate further strengthening of this event through the end of the year.

Drought conditions have gradually increased across portions of the southern and southeastern United States during the past two months, with significant dryness now spreading north into the eastern Corn Belt. It is expected that much of the southern Plains and southeastern U.S. will continue the trend of below normal moisture and above normal temperatures through much of the fall and winter. It is possible that one or more tropical systems could impact the region through early November and bring a temporary respite from the persistently dry weather.

The weather in October will determine how widespread a drought will be for the next growing season, says Indiana climatologist Dev Niyogi. La Niña conditions -- cooler-than-normal Pacific Ocean surface temperatures -- have been shifting temperatures and rainfall across the country.

Most parts of Indiana now are experiencing at least abnormally dry conditions, according to the U.S. Drought Monitor released Thursday (Sept. 30). Southern Indiana could move into extreme drought without rain soon, Niyogi said. That could result in mandated water restrictions in the affected counties.

"During La Niña, we are particularly prone to drought in March, but we will watch the conditions, including land-falling tropical systems, snow and precipitation, in the winter to see what sort of deficit we end up with, " he said.

The significant increase in hurricane activity during September within the Atlantic basin can be directly attributed to this unfolding event as waves exiting western Africa and moving into the eastern Atlantic are encountering reduced wind shear aloft. During the past three weeks, virtually every wave exiting the African coast has formed into a tropical system.

Hurricane climatology would suggest that tropical storm and hurricane formation will shift from the eastern Atlantic to the western Atlantic, Caribbean Sea, and Gulf of Mexico. Any systems moving into the eastern Gulf of Mexico will encounter above normal sea surface temperatures and hurricane strengthening could be explosive, similar to what was experienced five years ago when Katrina and Rita obtained major hurricane status.

Source: University of Nebraska, Purdue University