Freitag, 1. August 2014

Tropical Storm Bertha

Bertha is a sheared tropical cyclone with the center located on the
western edge of the deep convection as indicated by satellite. The
low-level circulation continues to be vigorous, but given the
current westerly shear the outflow is very limited. There are no
reasons to change the initial intensity which is kept at 40 knots.
Another Air Force reconnaissance plane will investigate Bertha in
the next several hours.
The current shear environment is not particularly favorable for
strengthening, but there are some indications by the global models
that the shear could decrease some as Bertha moves across the
northeastern Caribbean Sea. This should allow some slight
intensification during the next 24 to 36 hours. Once Bertha's
circulation moves away from Hispaniola beyond 48 hours, there is an
opportunity for additional strengthening if the shear becomes
lighter as suggested by global and statistical models. At this time,
the NHC forecast keeps Bertha with 45-knot winds over the
western Atlantic until it becomes more certain that the shear could
Bertha continues racing toward the west-northwest or 290 degrees
at 17 knots. The cyclone is being steered by the flow around the
Atlantic subtropical ridge which is forecast to persist. Once in
the western Atlantic near the eastern Bahamas, Bertha will be
steered by the southerly flow between the subtropical high
and a mid-level trough over the eastern United States. This pattern
will force Bertha to turn northward with a decrease in forward speed
and to eventually recurve northeastward over the Atlantic. 
The confidence in the track forecast, primarily in the next 2 to 3
days, is high since most the guidance is tightly clustered. The
confidence decreases after 3 days when the guidance becomes
divergent. The track envelope, however, brings Bertha northward
and then northeastward over the Atlantic, and the NHC forecast
follows closely the multi-model consensus.
Forecast positions and Max winds
Init  01/0900z 13.0n  57.0w   40 kt  45 mph
 12h  01/1800z 14.0n  59.6w   40 kt  45 mph
 24h  02/0600z 15.5n  63.0w   40 kt  45 mph
 36h  02/1800z 17.2n  66.0w   45 kt  50 mph
 48h  03/0600z 19.5n  68.8w   45 kt  50 mph
 72h  04/0600z 24.5n  73.5w   45 kt  50 mph
 96h  05/0600z 29.0n  74.0w   45 kt  50 mph
120h  06/0600z 35.0n  67.5w   45 kt  50 mph