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TD 16 dumping torrential rains; extreme rainfall event for North Carolina

By: Dr. Jeff Masters, 1:54 PM GMT on September 29, 2010

Tropical Depression Sixteen is dumping torrential rains on Jamaica, Cuba, the Cayman Islands, South Florida, and the western Bahamas as it tracks steadily north-northeastwards up the U.S. East Coast. Some rain amounts from TD 16 since yesterday morning include 8.13" at Irwindale in western Jamaica, 4.75" in George Town, Cayman Islands , and 4.34" in Jucaro, Cuba. In South Florida, radar-estimated rainfall amounts of 6 - 8" are common across the Middle and Upper Keys and between West Palm Beach and Fort Pierce (Figure 1.)

Surface observations don't show any winds in excess of 25 mph near the center of TD 16, and the strongest winds associated with the storm continue to be at at Buoy 42057 400 miles to the south of Cuba, where winds were 34 mph, gusting to 43 mph, at 9:24am EDT this morning. Radar loops out of Pico San Juan, Cuba shows a region of very heavy rainfall crossing Central Cuba, and these heavy rains will move through Southeast Florida and the Western Bahamas throughout the day. Satellite imagery continues to show that TD 16's heavy thunderstorms are poorly organized, but cover a very large region of the Caribbean, western Bahamas, and eastern Florida. The thunderstorms are slowly growing more organized, and TD 16 will probably be Tropical Storm Nicole later today. An Air Force hurricane hunter aircraft is currently approaching TD 16, and will give us a better idea on its status shortly.

Figure 1. Radar-estimated precipitation for South Florida. TD 16 has brought 6 - 8 inches of rain to the Middle and Upper Keys and between West Palm Beach and Fort Pierce.

Forecast today for TD 16
Because TD 16 is so large and poorly organized, it will take it considerably more time than is usual for a tropical depression to intensify. The wind shear is moderate, 10 - 20 knots, and the waters underneath are very warm, but the storm also has to contend with passage of the center over Cuba and South Florida. All these factors considered, the strongest TD 16 is likely to get today is a 45-mph tropical storm. By tonight, wind shear will increase to the high range, 20 - 30 knots, limiting the opportunity for further intensification. Winds in South Florida should remain below 35 mph for the duration of the storm, but may reach 40 - 45 mph in the western Bahamas and in Central and Western Cuba. Since TD 16 is a large storm, heavy rain will continue to be a threat for Cuba, South Florida, and the western Bahamas through Thursday morning.

Extreme rainfall for eastern North Carolina
In North Carolina, the arrival of TD 16 is shaping up to give coastal regions one of their top five rainiest weeks in history. Tropical moisture feeding into the region ahead of TD 16 has already brought 12.88" of rain to Wilmington, NC Sunday through Tuesday, and an additional 2.37" has already fallen there so far this morning. This gives Wilmington a 4-day total of 15.25", which is the second highest 4-day total in history, behind the 19.06" that fell in September 1999 during Hurricane Floyd. A non-tropical low pressure system is predicted to develop off the Florida East Coast this afternoon and move past North Carolina late tonight, giving North and South Carolina an additional helping of heavy rain before the main rains from TD 16 arrive Thursday morning and afternoon. By the time the rains from TD 16 finally clear the area Thursday night, an additional 5 - 10 inches will have fallen, and Wilmington will probably be looking at a 4-day rainfall total of 20 - 25 inches. Severe and damaging flooding is likely. Fortunately, eastern North Carolina was under moderate drought conditions prior to this week's rainfall onslaught, so the flooding damage will not be as great as the billions of dollars of damage wrought by Hurricane Floyd.

Figure 2. Forecast precipitation for the 5-day period from 8am today through 8am EDT Monday, October 4, 2010. Image credit: NOAA Hydrometeorological Prediction Center.

Mexican landslide not as deadly as first reported
Early reports that hundreds of Mexicans may have perished in a landslide generated from the rains from the remnants of Tropical Storm Matthew turned out to be wrong. The latest news from Mexico's mountainous Oaxaca state, where the landslide occurred, is that no one has died, though eleven people are missing. Matthew hit Belize on Saturday as a minimal tropical storm with 40 mph winds, and dissipated Sunday over southern Mexico. However, Matthew's remains stalled out over the region of Mexico that had already received torrential rains from Hurricane Karl, which hit on September 18. Satellite estimates of Matthew's rains over southern Mexico show that a foot of rain may have fallen in the landslide area. Matthew's remains still linger over the region, but are probably only capable of bringing one inch of additional rain through Thursday.

Elsewhere in the tropics
A tropical wave a few hundred miles east of the Lesser Antilles Islands is generating a modest amount of disorganized heavy thunderstorms. The wave is under a moderate 10 - 20 knots of wind shear, and has some dry air to the northwest of it that is interfering with development. None of the models develop this disturbance, and NHC is giving it a 10% chance of developing into a tropical depression by Friday.

Disturbed weather will continue in the Western Caribbean for at least the next ten days, and the NOGAPS and GFS models predict that the region could spawn a tropical depression 6 - 7 days from now. However, the models are being less aggressive than earlier this week in suggesting such a development. The NOGAPS model is also suggesting that two tropical waves between the Lesser Antilles Islands and coast of Africa could develop, 6 - 8 days from now, as they pass just northeast of the Lesser Antilles Islands. The first of those waves is currently located about 400 miles southwest of the Cape Verdes Islands.

Next update
I'll have updates as the situation with TD 16 requires.

Jeff Masters
This one fizzeld out

Flood Hurricane

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