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Tropical Depression BONNIE Forecast Discussion Number 11
2016-05-30 10:58:14| National Hurricane Center (Atlantic)
Issued at 500 AM EDT MON MAY 30 2016 000 WTNT42 KNHC 300858 TCDAT2 TROPICAL DEPRESSION BONNIE DISCUSSION NUMBER 11 NWS NATIONAL HURRICANE CENTER MIAMI FL AL022016 500 AM EDT MON MAY 30 2016 Radar and surface observations indicate that Bonnie has moved eastward and is now located along the coastline just east of Charleston, South Carolina. A late-arriving RapidSCAT pass from 0029 UTC showed several 25-27 kt surface wind vectors in a rain-free area 50-80 nmi south-southwest of the center. Since that time, some modest shower activity has developed in that same region, which supports maintaining Bonnie as a 25-kt depression on this advisory. The initial motion estimate is 040/04 kt. Bonnie is expected to remain a vertically shallow low pressure system throughout the forecast period, and should be steered slowly northeastward to east-northeastward by an approaching 700-500 mb shortwave trough that is expected to capture the small cyclone within the next 12 hours or so based on recent trends in water vapor satellite imagery. By Wednesday, Bonnie's forward speed is expected to increase as the cyclone moves along the northern side of the Bermuda-Azores subtropical ridge. This steering pattern should take Bonnie and its remnants across the coastline of the Carolinas during the next 2-3 days, and then offshore into the western Atlantic Ocean by days 4 and 5. The NHC track forecast is similar to the previous advisory track, and remains close to the GFS-ECMWF model consensus. Bonnie has been convectively challenged for the past 12 hours. Only narrow bands of weak to moderate convection have persisted near the center over land during the past 6 hours, and limited convection been developing over adjacent Atlantic waters. Furthermore, the 0000 UTC Charleston, South Carolina upper-air sounding showed than Bonnie was barely holding on to warm-core, tropical cyclone status with only 1 deg C warmer temperatures than the surrounding environment indicated between 500-300 mb. Given the dry mid-level air that overlays the cyclone and continued moderate-to-strong southerly vertical wind shear for the next 48 hours or so, any significant re-strengthening appears unlikely while Bonnie remains over near the cool coastal shelf waters. The SHIPS and LGEM models re-strengthen Bonnie back to tropical storm status by 36 hours, but this seems unlikely given that the cyclone will be over 22-24 deg C sea-surface temperatures and in proximity to land. The official intensity forecast calls for Bonnie to maintain its current intensity of 25 kt throughout the forecast period and become a remnant low pressure system by 48 hours. However, the latter could occur sooner than the official forecast is indicating. The primary concern from Bonnie continues to be locally heavy rainfall. Rainfall amounts of 6 to 8 inches have already been reported in portions of eastern Georgia and southern South Carolina, and additional rainfall amounts of 2 to 4 inches will be possible. FORECAST POSITIONS AND MAX WINDS INIT 30/0900Z 33.0N 79.5W 25 KT 30 MPH 12H 30/1800Z 33.3N 79.0W 25 KT 30 MPH 24H 31/0600Z 33.5N 78.4W 25 KT 30 MPH 36H 31/1800Z 33.8N 77.8W 25 KT 30 MPH 48H 01/0600Z 34.4N 77.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 02/0600Z 35.7N 75.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 03/0600Z 37.3N 72.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 04/0600Z 38.7N 69.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Stewart
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