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Tropical Storm Debby Discussion Number 5

Wiki-Hurricanes Forecast Center

11:00 AM AST Wed Aug 8 2018

The tropical transition of Debby this morning was quite unexpected given the system's latitude above 40°N latitude. In fact, it took me a moment to verify that this morning's satellite imagery for Debby was in fact Debby. Perhaps this should not be too surprising given that lapse rates were quite high with a deep layer thermal differential in excess of 80°C, so it appears that Debby has cold tropopause temperatures to thank for its tropical transition. Visible and infrared pictures from this morning show a well-defined spiral circulation, which at one point showed a fairly classic primordial curved band structure, with 1006Z microwave data from SSMIS showing some early banding features. Raw UW-CIMSS ADT values have climbed once again to T2.8/42kt, in agreement with TAFB yielding T3.0/45kt. SAB appears to be a low outlier with their T1.0/25kt estimate. Scatterometer data are more in agreement with the higher values, and a blend between the two higher values indicates an intensity of 45 kt.

Debby is not expected to last very long as a tropical system. The tropical storm is currently moving north in response to an approaching shortwave trough over Newfoundland and Labrador. Debby should turn towards the northest before the trough absorbs the tropical storm as anticipated by model guidance. During the course of the day today, Debby should be able to maintain its intensity thanks to divergent flow aloft and a deep-layer thermal differential peaking as high as +81.8°C, supportive of good convective activity. Still, there is little Debby can do before absorption occurs in an estimated 36 hours.

FORECAST POSITIONS AND MAX WINDS

INIT 08/1500Z 45 KT 50 MPH

12H 09/0000Z 45 KT 50 MPH

24H 09/1200Z 40 KT 45 MPH

36H 10/0000Z...DISSIPATED

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