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Subtropical Storm Andrea Discussion Number 1

Wiki-Hurricanes Forecast Center

11:00 PM AST Mon May 20 2019

An aircraft reconnaissance aircraft investigating the area of disturbed weather southwest of Bermuda earlier this afternoon found a well-defined center and tropical storm-force winds, leading to the formation of Subtropical Storm Andrea shortly after 21z. Since that time, deep convection has persisted mainly north of the low-level circulation. A 0043z ASCAT pass showed one 35kt barb and one 40kt barb even though it missed most of the circulation. Under the assumption these values are legitimate, the initial intensity is set to 40kt. Andrea continues to interact with an upper-level low in close proximity to its southwest, therefore it remains a subtropical storm at this time.

Andrea is currently experiencing strong wind shear from the aforementioned cold-core low, but this shear should decrease overnight as a small anticyclone becomes established aloft. Furthermore, although ocean temperatures are under 24C, and mid-level relative humidity values are drier than 60 percent, 200mb temperatures are running around -58; this is a good 6C cooler than normal. The difference between the ocean surface and extremely cold air aloft should provide plenty of instability to fuel Andrea for the next 12-18 hours, and some intensification is possible during that time. Thereafter, the current pattern of strong upper-level divergence is expected to become rapidly convergent, which should suppress convective development and cause weakening. By Wednesday afternoon, Andrea should merge with an approaching frontal boundary.

The cyclone is currently moving steadily north, and a turn toward the east is expected during the day tomorrow. This trajectory should continue through dissipation. On the forecast track, Andrea should pass south of Bermuda as a weakening tropical cyclone, with only fringe impacts expected there.

FORECAST MAX WINDS

INIT 21/0300Z 40 KT 45 MPH

12H 21/1200Z 45 KT 50 MPH

24H 22/0000Z 40 KT 45 MPH

36H 22/1200Z 30 KT 35 MPH

48H 23/0000Z...DISSIPATED/ABSORBED BY FRONT

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