674 
 WTNT42 KNHC 282041
 TCDAT2
 
 TROPICAL STORM BONNIE DISCUSSION NUMBER   5
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL022016
 500 PM EDT SAT MAY 28 2016
 
 A 1431Z ASCAT-B overpass indicated two 34-kt wind vectors existed in
 the northwest quadrant of the tropical cyclone in a region of deep
 convection that was not sampled during the earlier reconnaissance
 mission. Convection briefly weakened, but has redeveloped and
 persisted in that same part of the storm circulation for the past 5
 hours. Furthermore, NOAA Doppler velocity radar data from Charleston
 and Jacksonville have indicated winds ranging from 50-55 kt between
 15,000 and 20,000 feet in the same area of the 34-kt ASCAT wind
 vectors. Based on these data, the depression has been upgraded
 to Tropical Storm Bonnie.
 
 The initial motion estimate is 320/09 kt. The exposed low-level
 center near the southeastern edge of the deep convective cloud
 canopy has been easy to track over the past several hours, and has
 essentially been moving along the previous forecast track. The NHC
 model guidance remains in good agreement on Bonnie gradually turning
 toward the north-northwest as it moves around the west side of a
 deep-layer ridge, and moving onshore between Charleston and
 Beaufort, South Carolina, in about 18-24 hours. After landfall a
 mid-level shortwave trough moving northeastward out of the
 Mississippi Valley region is expected to significantly weaken the
 ridge, causing the steering to collapse. The result is that Bonnie
 is forecast to stall or meander along the coastal region of South
 Carolina in 24-36 hours before drifting off to the east or northeast
 by 48 hours. The NHC forecast track is similar to the previous
 advisory track, and closely follows a blend of GFS and ECMWF models.
 
 Bonnie is currently moving over the axis of warmest Gulf Stream
 sea-surface temperatures of 27-28 deg C. Although slightly cooler
 shelf water lies ahead of the cyclone, those ocean conditions do
 not appear to be sufficient to significantly weaken Bonnie based on
 rather vigorous convection that has developed just offshore of
 South Carolina today. However, southerly vertical wind shear of at
 least 20 kt is expected to prevent any rapid or significant
 intensification before landfall. After 24 hours, land interaction
 and the aforementioned wind shear should induce slow weakening,
 although there could be some convective rain bands over water
 producing wind gusts to tropical-storm force until about 48 hours.
 The official intensity forecast is similar to the previous advisory
 and follows the Decay-SHIPS model.
 
 The primary impact from Bonnie is expected to be locally heavy
 rainfall.
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  28/2100Z 31.1N  79.4W   35 KT  40 MPH
  12H  29/0600Z 31.9N  80.1W   40 KT  45 MPH
  24H  29/1800Z 32.8N  80.5W   35 KT  40 MPH...INLAND
  36H  30/0600Z 33.2N  80.1W   30 KT  35 MPH...INLAND
  48H  30/1800Z 33.5N  79.4W   30 KT  35 MPH...INLAND
  72H  31/1800Z 34.5N  77.8W   25 KT  30 MPH...INLAND
  96H  01/1800Z 35.0N  76.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 120H  02/1800Z 35.7N  75.3W   25 KT  30 MPH...POST-TROP/REMNT LOW
 
 $$
 Forecaster Stewart