[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 300858
TCDAT2

TROPICAL DEPRESSION BONNIE DISCUSSION NUMBER  11
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL022016
500 AM EDT MON MAY 30 2016

Radar and surface observations indicate that Bonnie has moved
eastward and is now located along the coastline just east of
Charleston, South Carolina. A late-arriving RapidSCAT pass from 0029
UTC showed several 25-27 kt surface wind vectors in a rain-free area
50-80 nmi south-southwest of the center. Since that time, some
modest shower activity has developed in that same region, which
supports maintaining Bonnie as a 25-kt depression on this advisory.

The initial motion estimate is 040/04 kt. Bonnie is expected to
remain a vertically shallow low pressure system throughout the
forecast period, and should be steered slowly northeastward to
east-northeastward by an approaching 700-500 mb shortwave trough
that is expected to capture the small cyclone within the next 12
hours or so based on recent trends in water vapor satellite imagery.
By Wednesday, Bonnie's forward speed is expected to increase as the
cyclone moves along the northern side of the Bermuda-Azores
subtropical ridge. This steering pattern should take Bonnie and its
remnants across the coastline of the Carolinas during the next 2-3
days, and then offshore into the western Atlantic Ocean by days 4
and 5. The NHC track forecast is similar to the previous advisory
track, and remains close to the GFS-ECMWF model consensus.

Bonnie has been convectively challenged for the past 12 hours. Only
narrow bands of weak to moderate convection have persisted near the
center over land during the past 6 hours, and limited convection
been developing over adjacent Atlantic waters. Furthermore, the 0000
UTC Charleston, South Carolina upper-air sounding showed than Bonnie
was barely holding on to warm-core, tropical cyclone status with
only 1 deg C warmer temperatures than the surrounding environment
indicated between 500-300 mb. Given the dry mid-level air that
overlays the cyclone and continued moderate-to-strong southerly
vertical wind shear for the next 48 hours or so, any significant
re-strengthening appears unlikely while Bonnie remains over near the
cool coastal shelf waters. The SHIPS and LGEM models re-strengthen
Bonnie back to tropical storm status by 36 hours, but this seems
unlikely given that the cyclone will be over 22-24 deg C sea-surface
temperatures and in proximity to land. The official intensity
forecast calls for Bonnie to maintain its current intensity of 25 kt
throughout the forecast period and become a remnant low pressure
system by  48 hours. However, the latter could occur sooner than
the official forecast is indicating.

The primary concern from Bonnie continues to be locally heavy
rainfall. Rainfall amounts of 6 to 8 inches have already been
reported in portions of eastern Georgia and southern South Carolina,
and additional rainfall amounts of 2 to 4 inches will be possible.

FORECAST POSITIONS AND MAX WINDS

INIT  30/0900Z 33.0N  79.5W   25 KT  30 MPH
 12H  30/1800Z 33.3N  79.0W   25 KT  30 MPH
 24H  31/0600Z 33.5N  78.4W   25 KT  30 MPH
 36H  31/1800Z 33.8N  77.8W   25 KT  30 MPH
 48H  01/0600Z 34.4N  77.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  02/0600Z 35.7N  75.6W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  03/0600Z 37.3N  72.9W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  04/0600Z 38.7N  69.0W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Stewart
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