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Tropical Storm BERTHA Forecast Discussion (Text)


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000
WTNT43 KNHC 012048
TCDAT3

TROPICAL STORM BERTHA DISCUSSION NUMBER   4
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL032014
500 PM AST FRI AUG 01 2014

Earlier observations from an Air Force Reserve Hurricane Hunter
aircraft and recent surface observations from Martinique indicate
that Bertha still has a closed circulation, although the area of
westerly winds south of the center is rather small.  The aircraft-
reported pressures were 1006-1007 mb, and the Martinique data
suggests a current central pressure of 1007 mb.  Based on this and
the aircraft wind data, the initial intensity remains 45 kt.  New
convection is currently developing in this bands near the center,
with a more solid area of convection farther east.

The initial motion is now 290/21.  Bertha continues to be steered
west-northwestward by the flow around the Atlantic subtropical ridge
and this should continue for the next 36-48 hours.  After that time,
the cyclone is expected to turn northward into a break in the ridge
caused by a deep-layer trough over the eastern United States.  This
motion should be followed by recurvature into the westerlies over
the Atlantic between Bermuda and New England, and then by a
northeastward motion over the open North Atlantic.  While the track
guidance has nudged a little to the left since 6 hours ago, it
remains in good agreement with this scenario.  The new forecast
track is therefore tweaked just a little to the left of the previous
track, and it is a little faster than the previous track after
recurvature.

Bertha continues to experience about 15 kt of southwesterly vertical
wind shear, and a combination of water vapor imagery and microwave
total precipitable water shows abundant dry air near the storm.  The
forecast track calls for Bertha to interact with one or two upper-
level troughs during the next 48 hours or so, which should cause
some shear and dry air entrainment to continue.  This, combined with
the current lack of organization, suggests little change in strength
should occur during that time.  This part of the new intensity
forecast is unchanged from the previous forecast. Subsequently,
Bertha is expected to move into an environment of less shear and
greater moisture.  The intensity guidance responds to this by
forecasting significant intensification, with several models showing
Bertha becoming a hurricane during recurvature.  Based on this, the
latter part of the intensity forecast is nudged upward from the
previous forecast, although it is still weaker than most of the
guidance.  An alternative scenario remains possible: that a
combination of shear, dry air entrainment, and land interaction
causes Bertha to degenerate to a tropical wave during the next 48
hours, followed by possible regeneration in the 72-120 hours when
the system reaches the more favorable environment.


FORECAST POSITIONS AND MAX WINDS

INIT  01/2100Z 14.9N  61.2W   45 KT  50 MPH
 12H  02/0600Z 16.0N  63.8W   45 KT  50 MPH
 24H  02/1800Z 17.8N  66.9W   45 KT  50 MPH
 36H  03/0600Z 19.9N  69.6W   45 KT  50 MPH
 48H  03/1800Z 22.4N  72.0W   45 KT  50 MPH
 72H  04/1800Z 27.5N  74.0W   50 KT  60 MPH
 96H  05/1800Z 33.5N  71.0W   55 KT  65 MPH
120H  06/1800Z 38.5N  62.0W   60 KT  70 MPH

$$
Forecaster Beven



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Page last modified: Friday, 01-Aug-2014 20:49:08 UTC