Taste of autumn; Irma threatens U.S.

Published 7:00 am Tuesday, September 5, 2017

By Skip Rigney

Our first taste of autumn will arrive on Wednesday. Meanwhile, Hurricane Irma will continue westward across the Atlantic Ocean for the next few days before making a sharp turn northward.

On Sunday a strong cold front moved southward from Canada into Montana and North Dakota. In the warm air just south of the front, people probably felt that they had been transported back to July. Temperatures soared into the upper 90s on Sunday in South Dakota and on Labor Day in parts of Missouri and Kansas.

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But, now that the cold front has passed south of those states, places such as St. Louis and Kansas City are feeling cool, dry north winds. Their high temperatures for the next few days will be in the 70s and their lows near 50 degrees.

Instability in the atmosphere associated with this front will kick up scattered showers and thunderstorms in our area today, tonight, and Wednesday as it approaches.

This is unlikely to be a big rain event. Locations in Pearl River County that do receive rainfall will probably get less than one-half inch.

The National Weather Service predicts the cold front will pass through south Mississippi sometime Wednesday. After the front passes cooler air will begin to filter into the area on a north wind.

Thursday and Friday are shaping up to be gorgeous days with early morning lows in the upper 50s and highs in the low 80s. Best of all will be the dry feel to the air with dew point temperatures in the 50s compared to typical summer dew points in the 70s.

Meanwhile, Hurricane Irma is forecast to be southeast of Florida by Friday or Saturday.

If Irma were to continue its west-northwestward motion, it would end up in the Gulf of Mexico. However, computer modeling indicates that it is more likely that Irma will take a sharp right turn and head northward.

The reason for the turn is that in upper levels of the atmosphere, between about four and ten miles winds altitude, over the Gulf and southeastern United States winds are predicted by the models to be blowing from the west. As Irma encounters those winds, it should begin to turn northward.

The key question is when the turn happens. At this point it is not clear whether the northward turn will steer Irma into Florida, the Carolinas, or further up the East Coast.  Unfortunately, at this time a landfall somewhere in the U.S. appears likely.

For now, it looks like those of us on the north central Gulf Coast will be protected by the upper altitude west winds above us. However, the upper wind pattern over the central and eastern United States is more complex and unpredictable than usual this week with several waves in the wind and pressure patterns interacting.

So, we cannot be certain that we are out of reach of Irma quite yet. It should be easy to keep up on Irma’s predicted path this week, since its threat to Florida will likely dominate the national news.

Meanwhile, enjoy the coming preview of fall here in the Gulf South.