Alberto exits, hotter air moves our way

Published 7:00 am Wednesday, May 30, 2018

By Skip Rigney 

The remainder of the work week we will see fairly typical summer weather, but by the weekend there is a chance of warmer-than-normal temperatures overspreading south Mississippi and the surrounding Gulf Coast region.

The remnant low pressure system that was once Subtropical Storm Alberto is drifting northward across Tennessee  toward the Ohio River Valley and the Great Lakes where it will bring rain to cities such as Louisville, Indianapolis, and Chicago.

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As of Monday morning, Subtropical Storm Alberto was poised to become only the fifth tropical or subtropical storm or hurricane to make landfall in the Gulf of Mexico in the month of May. The Atlantic tropical storm season officially begins on June 1st, but sometimes nature does not adhere to the calendar put out by the National Hurricane Center in Miami.

You may have noticed that Alberto was referred to as a subtropical rather than tropical storm.

Tropical storms and hurricanes derive the vast majority of their energy from the evaporation of warm ocean waters and the subsequent release of heat energy into the air that occurs when the water vapor condenses into clouds in the storm’s core.

Subtropical storms get some of their energy from this same process of heat transfer through water evaporation and condensation.

However, subtropical systems also gain some of their strength through a different process, which is similar to the way winter storms gain strength. This non-tropical process depends on horizontal temperature differences.

Storms that gain energy from both of these processes are referred to as “subtropical” because of their hybrid or dual nature.

Subtropical storms are most likely to occur when both energy processes are at play. Not surprisingly that most often occurs very early or very late in the tropical season.

Alberto fit that description. Not only did it gain energy from the warm waters of the Gulf of Mexico, Alberto also strengthened through interaction with a trough of cooler temperatures and lower pressures about six miles aloft in the atmosphere, which moved from the Great Plains southeastward over the Gulf of Mexico.

Subtropical storms tend to be very lopsided with most of the wind and rain to the east of the storm. This also was true in Alberto’s case, which meant that those of us 200 miles west of the track didn’t notice much unusual, while those 200 miles east of the track saw significant rain.

Alberto is leaving behind a trough of lower atmospheric pressures across the middle South. These lower pressures will help scattered thunderstorms to pop up over the next several days in the fairly typical warm, humid June air. By the weekend the eastern edge of a large, hot area of high pressure will expand from Mexico and Texas toward us. Our afternoon high temperatures, which will be in the low 90s the next few days, will climb into the middle and perhaps even upper 90s over the weekend and into early next week. As disturbances in the upper atmosphere travel along the eastern side of the high and pass over the hot air near the surface, they may spark some strong thunderstorms Saturday and Sunday.

If storms develop early enough in the day they could produce enough cloud cover to keep the extra hot temperatures currently forecast from occuring.