264 
 WTNT43 KNHC 050859
 TCDAT3
 
 TROPICAL STORM BERTHA DISCUSSION NUMBER  18
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL032014
 500 AM EDT TUE AUG 05 2014
 
 Data from an Air Force Reserve reconnaissance aircraft indicate
 that Bertha's winds have decreased below hurricane strength, which
 is logical given that little deep convection now exists near the
 center. The initial intensity has been lowered to 55 kt, which
 could generous given that only 45-kt surface winds have been
 reported thus far. However, the recon aircraft has not yet completed
 its entire mission, so I do not want to bring the intensity
 too quickly in the event stronger winds are found east of the center
 and/or deep convection redevelops.
 
 The initial motion estimate is an uncertain 015/19 kt. Bertha
 briefly accelerated to about 21-22 kt after losing its deep
 convection a few hours ago, but recon fix data suggests that the
 cyclone's motion has settled down to around 19 kt now. Overall, the
 official track forecast and philosophy remains basically unchanged.
 The NHC model guidance remains in very good agreement on Bertha
 continuing its northeastward trek around the western periphery of a
 deep-layer subtropical ridge for the next 24 hours or so, and then
 accelerate eastward after getting caught up in the mid-latitude
 westerlies by 36-48 hours. The official forecast track is similar to
 but slightly west of the previous advisory track to account for the
 more westward initial position, and closely follows the consensus
 model TVCA.
 
 Bertha is forecast to experience increasing vertical wind shear
 over the next two days, with the shear reaching 50 kt or more by
 24-36 hours. The combination of the strong shear and decreasing SSTs
 should induce steady weakening and cause extratropical transition
 by 36 hours or so. However, not as much weakening is expected with
 such strong shear conditions due to the expected infusion of
 baroclinic energy associated with a strong mid-latitude trough that
 is forecast to capture Bertha by 48 hours, which will help maintain
 the cyclone's intensity. The intensity forecast during the
 extratropical phase closely follows input from the NOAA Ocean
 Prediction Center.
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  05/0900Z 33.4N  72.9W   55 KT  65 MPH
  12H  05/1800Z 35.9N  70.8W   55 KT  65 MPH
  24H  06/0600Z 38.6N  66.9W   50 KT  60 MPH
  36H  06/1800Z 41.3N  62.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
  48H  07/0600Z 44.1N  56.4W   50 KT  60 MPH...POST-TROP/EXTRATROP
  72H  08/0600Z 48.5N  44.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
  96H  09/0600Z 49.3N  28.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 120H  10/0600Z 50.3N  14.5W   45 KT  50 MPH...POST-TROP/EXTRATROP
 
 $$
 Forecaster Stewart