This week, a deep layer of tropical moisture is moving northwards from the Gulf of Mexico, producing conditions that are ideal for severe thunderstorms and flash flooding in the Southeast as the effects of El Niño become stronger.
Marginal Risk for Severe Weather
A marginal risk (that is, level 1 out of 5) of severe weather has been issued by the Storm Prediction Center for parts of Alabama, Georgia, and the Florida Panhandle today, with some severe storms possibly causing damaging wind gusts, large hail, and short-lived tornadoes; the most significant threat will occur between 2 PM and 8 PM local time, especially in the area along and in front of a slowly moving cold front.
Several of the communities classified as being under the highest concern include Panama City, Mexico Beach, and Apalachicola, since over the last two weeks they have experienced repeated tropical downpours which have completely saturated the soil. Further heavy rain could soon cause flash flooding, in particular in low-lying areas and in places near creeks and rivers that are already at a high level.
El Niño Pattern Strengthens
The weather activity this week is part of a wider pattern which is expected to control the Southeast throughout the fall and winter as El Niño conditions become stronger in the Pacific. The Southeast has the greatest chance of any area in the United States for an October that is wetter than average, precipitation amounts possibly reaching 2 to 4 inches above normal in Alabama, Georgia and northern Florida.
According to David DeWitt, a forecaster with the CPC, the El Niño signal is becoming increasingly clear, since the typical pattern of increased storminess over the Gulf Coast and the Southeast is being observed and this is expected to persist for the next few months.
Temperature Roller Coaster
Although precipitation is the main feature of the forecast, temperatures are expected to vary greatly this week. Before the cold front arrives today, temperatures will be in the 80s over most of the Southeast and the heat index will make it feel more like mid-summer. On the other hand, behind the front the temperatures will fall by 15 to 20 degrees, so that on Thursday and Friday the highs will have difficulty reaching the upper 60s in certain areas.
The tendency for warm and humid air to clash with cold fronts at intervals is what causes the Southeast to have its most vigorous severe weather season, and people should stay alert, particularly in the late afternoon and evening when atmospheric instability reaches its peak.
Flood Danger Persists
The main worry is the increasing risk of flooding due to several instances of heavy rain. Places which have already seen between 6 and 10 inches of precipitation in the last two weeks do not have much more capacity to take in additional moisture. Flood watches have been issued by the National Weather Service for many rivers and streams in the area, and minor to moderate flooding is expected to persist throughout the weekend.
Cities are especially susceptible since the storm drains and retention ponds are already at or close to full capacity. People who commute should anticipate delays and possible road closures during the periods of heaviest rainfall.
