Standard summer pattern until tropical moisture arrives by Sunday
Some showers and thunderstorms will gradually work back into the weather through the end of the week. Appropriate for the time of year, there are a few items to watch in the Atlantic Basin.
The Tropics: Showers and thunderstorms have become more concentrated around a tropical wave (Invest 97L) over the central Caribbean Sea. The system will continue moving west until reaching the northwestern Caribbean. By then, a slower forward motion gives the disturbance an 80 percent chance of becoming a tropical depression.
Here is the first @NHC_Atlantic forecast advisory on Tropical Depression 13. It is expected to rake across the Virgin Islands and the Bahamas and then approach Florida, and possibly the Gulf of Mexico by early next week. I'll have a full analysis @WBRZ on News 2 at 10. pic.twitter.com/dXkqlYxXbp— Josh Eachus (@DrJoshWX) August 20, 2020
At this time, forecast model guidance continues to struggle with these two systems due to the lack of closed central circulations. With regard to track, both have the potential to reach the Gulf of Mexico. As far as strength goes, there is not currently any indication of either becoming very well organized. Keep in mind, tropical systems do not need to pack strong winds to produce heavy rain and forecast details will be highly subject to change until a system actually forms (if at all).
A large area of showers and thunderstorms, located over Guinea and Sierra-Leone, Africa, is associated with a vigorous tropical wave. Environmental conditions allow a 40 percent chance of development over the next 5 days as the wave enters the extreme eastern Atlantic. By early next week, however, conditions are forecast to become less favorable for tropical cyclone formation.
The Next 24 Hours: Skies will trend mostly clear overnight and the slightly drier air will allow low temperatures into the low 70s. Some isolated readings in the upper 60s are possible north of I-12. Thursday should bring a slight uptick in rain coverage even though humidity will still be a little lower than average. After highs make it into the low 90s, isolated to scattered showers and thunderstorms are expected in the afternoon—especially south and east of Baton Rouge. Gusty wind will be possible in any storms.
The Long Term Trend: Friday and Saturday, isolated showers and thunderstorms will stay in the forecast. Activity will be near the coast overnight and in the morning and inland during the afternoon. Each day, 30 to 40 percent measurable rain coverage is expected across the 13 Parish, 3 County forecast area. Highs will be in the low 90s with lows in the low 70s. By Sunday, tropical moisture will begin to surge into the region. This will make it feel stickier and allow scattered to widespread showers and thunderstorms into Monday. Tuesday and beyond, weather will be dictated by what occurs with tropical waves (Invest 97L, Invest 98L) moving across the Caribbean Sea and central Atlantic.
The Explanation: An unseasonably dry air mass will remain in place through Friday. Lower dew points will mean lower humidity. Since dry air heats and cools more efficiently than humid air, overnight lows will dip 1-3 degrees below average and afternoon highs will ride into the 90s. Fortunately, the steam will be subdued. This is all thanks to an upper level trough of low pressure over the Southeastern U.S. that will be pinched westward and over the local area Thursday through Saturday. With the axis of this trough nearby, there will be a combination of instability and lift for some showers and thunderstorms to develop. On the flip side, the atmosphere will be rather moisture deprived. Therefore, isolated to scattered (at most) coverage seems appropriate, but the drier air could allow for gusty winds in some storms. No single day looks more active than another does. By the weekend, the trough may start to flatten out a little bit, but the area will remain in a weak spot of lower pressure between a large Southwest U.S. ridge and a western Atlantic ridge. On Sunday, forecast models indicate deep tropical moisture returning to the area. At the very least, this will allow robust development in showers and thunderstorms and potentially some areas of heavy rain. Instability will be highest on Sunday and Monday, therefore those two days look like the busiest at this time. A ridge may try to build back over the region and subdue activity by the middle of next week, but with one or two tropical disturbances also in play, the forecast for Tuesday and beyond may change quite a bit.
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