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 588 
 WTNT44 KNHC 080834
 TCDAT4
 
 Tropical Storm Debby Discussion Number   4
 NWS National Hurricane Center Miami FL       AL042018
 500 AM AST Wed Aug 08 2018
 
 Over the past several hours, deep convection with cloud tops of -55
 to -60 deg C has developed in the southeastern semicircle, with
 some of the convective tops covering the previously exposed
 low-level circulation center. In addition, outer banding
 features have dissipated, and an elongated upper-level anticyclone
 has developed over the cyclone. These convective- and synoptic-scale
 features indicate that Debby has made the transition from a
 subtropical to a tropical cyclone. The initial intensity of 40 kt
 is based on a blend of UW-CIMSS ADT and SATCON intensity estimates
 of 39 kt and 42 kt, respectively. Furthermore, the 34-kt wind radii
 and radius of maximum winds (RMW) were decreased significantly on
 this advisory based on ASCAT wind data.
 
 The initial motion estimate is now 015/08 kt.  Debby has made the
 forecast turn toward the north-northeast, and a further turn toward
 the northeast is expected later today as the cyclone moves around
 the northwestern periphery of a deep-layer ridge and ahead of an
 approaching mid-level trough. The latest model guidance remains in
 good agreement on this developing track scenario, and the new NHC
 forecast track is similar to the previous advisory, and lies close
 to a blend of the track consensus models HCCA and FSSE.
 
 Debby will be moving along a tight sea-surface temperature (SST)
 gradient for the next 24-36 hours or so, with the northwestern half
 the circulation being over sub-25C SSTs and the southeastern
 semicircle being over warmer waters where convection could continue
 to develop. Given the relatively low vertical wind shear regime
 that the cyclone will be moving through, along with the possibility
 of deep convection persisting near the center, the intensity
 forecast calls for little change in strength today, followed by
 only slight weakening tonight and early Thursday. By Thursday night
 or early Friday, SSTs beneath the cyclone are expected to decrease
 to near 20 deg C and the shear is forecast to increase to more than
 20 kt, an unfavorable combination that should result in Debby
 dissipating over the far north Atlantic by 48 hours.
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  08/0900Z 40.8N  48.8W   40 KT  45 MPH
  12H  08/1800Z 41.8N  48.2W   40 KT  45 MPH
  24H  09/0600Z 43.2N  46.1W   35 KT  40 MPH
  36H  09/1800Z 44.5N  43.4W   30 KT  35 MPH
  48H  10/0600Z...DISSIPATED
 
 $$
 Forecaster Stewart
 
 
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