TROPICAL STORM HENRI DISCUSSION NUMBER 5
NWS NATIONAL HURRICANE CENTER MIAMI FL AL082015
1100 PM AST WED SEP 09 2015
Recently received ASCAT-B scatterometer data showed an area of 35-40
kt wind vectors in the convection about 75-100 n mi east of the
center. Based on this, the initial intensity is increased to a
possibly conservative 35 kt and the cyclone is upgraded to a
tropical storm. Despite the upgrade, Henri remains a disorganized
system, with the low-level center remaining exposed to the west of
the convection due to 15-20 kt of shear. In addition, microwave
satellite data and experimental European multispectral satellite
imagery suggest a tongue of dry air is entraining into the cyclone
around the west, south, and southeast sides of the circulation.
Henri has started its expected northward track with the initial
motion of 355/4. For the next 36-48 hours, the cyclone should move
generally northward with an increase in forward speed between the
subtropical ridge to the east and a deep-layer trough moving
eastward through the eastern United States. After that time, Henri
should turn northeastward and eastward as it enters the westerlies.
The new forecast track is similar to the previous track, but it lies
a little south of the center of the guidance envelope after 36 hours
due to a northward shift in the guidance.
The dynamical models suggest that the shear should subside during
the next 36-48 hours, and that the dry air entrainment should also
decrease. This combination should allow Henri to strengthen until
it reaches colder sea surface temperatures north of the Gulf Stream
in a little under 48 hours. After that, the cyclone is expected to
become extratropical as it merges with a frontal system. The new
intensity forecast calls for a peak intensity near 50 kt in 36-48
hours, followed by gradual weakening. The first 48 hours are in
best agreement with the SHIPS model, and the intensities after
extratropical transition are based on input from the NOAA Ocean
Prediction Center.
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