Will low pressure trough protect us from tropics?

Published 9:10 am Tuesday, August 30, 2016

As I write this on Monday morning, a tropical depression is creeping west-northwestward through the southeast Gulf of Mexico about two hundred miles west of Key West, Florida.

The National Hurricane Center in Miami (www.nhc.noaa.gov) forecasts that there is a chance by the time you read this on Tuesday that the depression will have strengthened into Tropical Storm Ian. Also, by the time you read this, it is forecast to have made a right turn and begun curving more toward the north.

Does that mean it is headed for us? You should definitely check the latest forecast track from the National Hurricane Center. This system, which began as a tropical wave in the Atlantic, has proven very difficult to forecast. Over the past week the best computer weather models in the world have jumped all over the place in terms of whether the system would intensify, and where it would go if it did develop.

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Fortunately, as of Monday morning when I write this, there is much better agreement between the models. All of these computer model simulations show that the most likely scenario, at least as of Monday morning, is that this tropical system will curve even more to the right on Wednesday and Thursday and eventually make landfall far to our east, probably somewhere on Florida’s Big Bend coast between Tampa and Tallahassee.

Several miles high in the atmosphere a large ridge of high pressure covering most of the south central and southeastern United States has been blocking the disturbance from turning north over the last few days. 

However, a strong trough of low pressure at those same altitudes is predicted by the models to sweep southeastward from the Great Lakes beginning today.

That upper trough is expected to weaken the high pressure currently over us. At first, the effect will be for the tropical system to turn northward toward us. Fortunately for us, the upper trough is forecast to strengthen and dig southward and eastward over the southern Atlantic seaboard states by Wednesday. This should cause brisk upper level southwesterly winds to form over the Gulf, sweeping whatever tropical depression or storm is in the Gulf northeastward into Florida.

That means that by Thursday and Friday we should be on the western, drier side of the tropical system. Expect hot temperatures with only isolated, if any, afternoon showers and thunderstorms. In other words, the only impact this tropical system is expected to have on our typical summer weather is to cut down on the number of afternoon showers.

Of course, the future tracks and especially future intensities of tropical cyclones are notoriously difficult to forecast. Keep up on the weather today through at least Thursday to make sure that those of us in Pearl River County don’t have any unwelcome surprises from Ian.

By the Labor Day weekend, the weather pattern in the Gulf of Mexico should have returned to normal. 

That means the outlook for our Labor Day weekend weather in south Mississippi is the typical late summer forecast: warm, humid, with a chance of afternoon thundershowers.

By Skip Rigney