2014-08-01 Tropical Storm Bertha has formed east of the Lesser Antilles and is presently threatening Antigua, the French and Dutch Antilles and likely the BVI and Puerto Rico later on the weekend.

BULLETIN
TROPICAL STORM BERTHA ADVISORY NUMBER 18
NWS NATIONAL HURRICANE CENTER MIAMI FL AL032014
500 AM EDT TUE AUG 05 2014

…AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT FINDS BERTHA HAS
WEAKENED TO A TROPICAL STORM…

SUMMARY OF 500 AM EDT…0900 UTC…INFORMATION
———————————————-
LOCATION…33.4N 72.9W
ABOUT 475 MI…765 KM W OF BERMUDA
MAXIMUM SUSTAINED WINDS…65 MPH…100 KM/H
PRESENT MOVEMENT…NNE OR 15 DEGREES AT 22 MPH…35 KM/H
MINIMUM CENTRAL PRESSURE…1005 MB…29.68 INCHES

WATCHES AND WARNINGS
——————–
THERE ARE NO COASTAL WATCHES OR WARNINGS IN EFFECT.

DISCUSSION AND 48-HOUR OUTLOOK
——————————
AT 500 AM EDT…0900 UTC…THE CENTER OF TROPICAL STORM BERTHA WAS
LOCATED NEAR LATITUDE 33.4 NORTH…LONGITUDE 72.9 WEST. BERTHA IS
MOVING TOWARD THE NORTH-NORTHEAST NEAR 22 MPH…35 KM/H. A TURN
TOWARD THE NORTHEAST WITH INCREASING FORWARD SPEED IS EXPECTED
TO OCCUR LATER TODAY…AND CONTINUE THROUGH WEDNESDAY. ON THE
FORECAST TRACK…BERTHA WILL PASS ABOUT MIDWAY BETWEEN THE U.S.
EAST COAST AND BERMUDA LATER THIS MORNING.

MAXIMUM SUSTAINED WINDS HAVE DECREASED TO NEAR 65 MPH…100 KM/H…
WITH HIGHER GUSTS…OVER A SMALL AREA NORTHEAST OF THE CENTER.
GRADUAL WEAKENING IS FORECAST DURING THE NEXT 48 HOURS.

TROPICAL-STORM-FORCE WINDS EXTEND OUTWARD UP TO 125
MILES…205 KM…PRIMARILY TO THE EAST OF THE CENTER.

THE MINIMUM CENTRAL PRESSURE RECENTLY REPORTED BY AN AIR FORCE
RESERVE RECONNAISSANCE AIRCRAFT WAS 1005 MB…29.68 INCHES.

HAZARDS AFFECTING LAND
———————-
NONE.

ROPICAL 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