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Tropical Storm BERTHA


500 AM EDT MON AUG 04 2014

Convection has been pulsing near the center, but the overall
convective cloud pattern of Bertha has changed little since the
previous advisory due to moderate northwesterly wind shear. Earlier
Air Force Reserve reconnaissance wind data around 0500 UTC supported
a 55-kt intensity, especially since the pressure had decreased 3 mb
down to 1004 mb. However, a NOAA research aircraft has just started
its investigation of the cyclone, and surface wind data support
increasing the intensity to 60 kt along with a central pressure
fall to about 999 mb.

Bertha is now moving northward or 350/14 kt. There remains no
significant change to the previous track forecast or reasoning. The
latest NHC model guidance remains tightly clustered and in
excellent agreement on Bertha continuing to move around the western
periphery of the Bermuda-Azores high pressure ridge for the next 36
hours or so, followed by a northeastward acceleration into the
mid-latitude westerlies ahead of a deep-layer trough and frontal
system currently approaching the U.S. east coast. The official
forecast track is just a tad to the left of the previous advisory,
and is close to the consensus model TVCA. The 72-, 96-, and 120-hour
positions are based on a blend of input from the NOAA Ocean
Prediction Center. On the forecast track, Bertha is expected to
pass about midway between the U.S. coast and Bermuda on Tuesday.

The northwesterly vertical wind shear that has been plaguing Bertha
for the past few days is now decreasing and is gradually backing
around to a southwesterly direction. In fact, the global models
indicate that Bertha will move underneath a 200 mb ridge axis in
18-24 hours, at which time we should see the cyclone reach hurricane
status. That intensity should be short-lived since the shear is
forecast to increase to more than 30 kt by 48 hours and beyond,
which should induce at least steady weakening. The intensity,
however, has been held higher than normal due to Bertha's expected
transition to an extratropical cyclone with possible baroclinic
energy keeping the system fairly strong. Extratropical transition is
expected by 72 hours, but it could occur sooner due to 50 kt or
more of shear and SSTs around 20C by that time. The NHC intensity
forecast is similar to the previous advisory, remaining above the
consensus models ICON and IVCN, and is close to a blend of the SHIPS
and LGEM intensity models.


INIT  04/0900Z 26.1N  73.6W   60 KT  70 MPH
 12H  04/1800Z 28.6N  73.7W   60 KT  70 MPH
 24H  05/0600Z 31.9N  72.9W   65 KT  75 MPH
 36H  05/1800Z 35.0N  70.8W   65 KT  75 MPH
 48H  06/0600Z 37.7N  67.0W   60 KT  70 MPH
 72H  07/0600Z 43.4N  57.3W   55 KT  65 MPH...POST-TROP/EXTRATROP
 96H  08/0600Z 47.5N  47.5W   50 KT  60 MPH...POST-TROP/EXTRATROP
120H  09/0600Z 49.5N  37.5W   45 KT  50 MPH...POST-TROP/EXTRATROP

Forecaster Stewart