WEATHER BLOG: Flash flood threat increasing tomorrow, tropics come alive

Weather

Surface observations show a weak surface low pressure has formed in the northwestern parts of the Gulf of Mexico. I believe this has concentrated the highest levels of moisture and rainfall offshore through today, which is why most of Acadiana lucked out and didn’t see the heavier rainfall. This surface feature, however, will be working northeastward into Acadiana through tonight and tomorrow, finally bringing these high-moisture levels onshore.

Precipitable water values of 2.5-2.8 inches could come ashore later tonight and through tomorrow. If you’re wondering what that means, this is almost 200% of normal or double the amount of moisture we usually see in the atmosphere this time of year. Given that we already see high-levels of moisture on average during the summer, moisture levels such as these could mean storms dumping very heavy rainfall. Some storms could dump 2-3 inches per hour in localized spots. This is almost like a tropical system, meaning radar could underestimate rainfall in spots.

In terms of totals, the highest rainfall totals should still remain along and south of I-10. This is one consensus that models tend to be wrapped around. A good average (area-wide) rainfall total forecast would be 2-5 inches through Monday afternoon. Like with any tropical rain threat, I believe you could double these numbers in isolated spots, meaning someone near the coast could get 8-10 inches if current high-resolution models are to be believed.

They heavily overestimated rainfall totals today, but that could be due to the developing low pressure area, causing the heavier rainfall to become more concentrated offshore. Before we are done with this system, this heavy rainfall will have to work onshore with the surface feature. These rainfall totals are not set in stone, and the heaviest rainfall could very easily stay offshore, but it’s good to be prepared in this type of scenario. A FLASH FLOOD WATCH has been extended through 1pm tomorrow.

Storms should become more scattered by Monday and Tuesday.

TROPICAL UPDATE

Busy times are beginning in the tropics as we have three areas to discuss. The first is the system that is currently giving us the heavier rainfall. This system is near the coast and not vertically stacked and fortunately it will not have enough time over water to develop into anything significant. Nonetheless, heavy rainfall will continue to accompany this system.

We also have a disturbance near the southeastern coast of Florida, which still has a high chance to develop into a tropical system as it works north and later northeast, into the open waters of the Atlantic.

Models are giving this system the possibility of deepening into a tropical system by the middle parts of next week, as it heads into the Atlantic.

We also now have Tropical Storm Dorian located east of the Lesser Antilles islands.

Models continue to deepen this system as it heads westward into the northeastern Caribbean by the middle parts of next week. The National Hurricane Center has the potential for a hurricane, approaching Hispaniola by the end of the forecast. With these long-track systems, it’s best to keep the forecast in 5-7 day increments, as it’s hard to know what this system could be or do beyond the 5-7 day time frame. We’ll just have to continue to monitor it through next week.

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