September 18, 2020

Tropical Depression #13 will meander around for a few days bringing excessively heavy rainfall to the northern Gulf Coast; Tropical Storm Katia may threaten the US east coast as a hurricane next week

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Rob Lightbown wrote that Tropical Depression 13 was fairly elongated on Friday (2) morning with poorly organised thunderstorm activity. The depression was experiencing some shear on its west side, however, environmental conditions will become more favourable this weekend and he expected this system to strengthen into an upper end tropical storm or possibly a Category 1 hurricane. Very heavy flooding rainfall will be the main threat with this slow moving meandering system.

Rob says: “The National Hurricane Center put the center of TD 13 near 26.5 North Latitude, 91.7 West Longitude at 5 am EDT/4 am CDT this morning. My analysis of satellite products from CIMSS indicates that the best low-level convergence and upper-level divergence is located further to the southeast near 25.8 North Latitude and 89 West Longitude. Given the fact that the centre is so broad, I suspect we will see the centre reform further to the southeast closer to the deep convection today. This could also allow this system a little more time to strengthen before it comes ashore next week.

After taking careful note of the European model forecast Rob noted: “This is a warning to everyone from southern and southeastern Louisiana eastward to southern Mississippi, southern Alabama and the western Florida Panhandle that we are looking at an extended period of tropical storm onshore winds with several days of very heavy rain likely. 10 to 20 inches of total rainfall is likely across this entire area. In addition, the onshore tropical storm force winds will cause a 2 to 4 foot storm surge across the northern Gulf coast this weekend.

“Finally, the model scenario posed by the European model is quite troubling. It forecasts very heavy rainfall and 30 to 50 mph east to southeast winds in the New Orleans metro area from today through Sunday followed by northerly winds of 30 to 50 mph on Monday and Tuesday. So, what could happen is that the water will pile up on the northern and northwestern shores of Lake Pontchartrain this weekend and then be pushed back out towards New Orleans on Monday and Tuesday. This is something that will need to be watched very closely.”

While these systems pose no immediate threat to the Cayman Islands, they should still be monitored carefully. Go to Crown Weather Services at  www.crownweather.com and to the National Hurricane Centre at www.nhc.noaa.gov/. We wish to thank Crown Weather for the permission to use their graphics and information. Please support them.

-NB. At the time of publication Tropical Depression #13 was upgraded to Tropical Storm Lee.

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