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Tropical Storm DANNY


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TROPICAL STORM DANNY DISCUSSION NUMBER   6
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042015
500 PM AST WED AUG 19 2015

Satellite imagery shows that Danny's deep convection collapsed late
this morning, with the experimental Saharan Air Layer (SAL) Meteosat
imagery suggesting that dry-air entrainment could be the cause.
Although visible satellite pictures still show a vigorous
circulation and some renewed convection, the system overall has lost
organization and become more embedded in the Intertropical
Convergence Zone since yesterday. With little change in the Dvorak
classifications, the initial intensity is kept at 45 kt in agreement
with the latest CI number from TAFB.

Given the current appearance of the cyclone, it might be that
dry air associated with the SAL intruding from the north and west
has become a greater impediment to intensification.  Dry air aside,
other atmospheric parameters governing intensification would seem to
favor some strengthening during the next 2 to 3 days, and the
official forecast shows modest strengthening.  After that time,
significantly drier mid-tropospheric air and an increase in westerly
flow aloft associated with an enhanced and persistent mid-oceanic
trough across the Caribbean region is expected to induce weakening
as shown in the ECWMF solution.  There is a large discrepancy
between the statistical and dynamical model guidance, with the
GFS-based statistical guidance continuing to show more
intensification and the regional hurricane models showing only
modest strengthening followed by weakening.  The official intensity
forecast is similar to but a little lower than the previous one at
later times, consistent with the multi-model consensus.

The cyclone has been moving generally west but at a slower forward
speed (280/08) in response to a weakening subtropical ridge to the
north of the cyclone.  A west-northwestward motion is expected
during the next next 2 to 3 days, at which time an interesting
split in the model guidance occurs.  The GFS shows a much stronger
representation of Danny moving west-northwestward near and north of
the Greater Antilles in 3 to 5 days.  The ECWMF solution, on the
other hand, depicts Danny as a shallower feature from the start and
as a weakening cyclone as it nears the Lesser Antilles on a westward
track.  The new forecast track maintains the philosophy of the
previous one by showing a general westward track in the extended
range, giving more weight to the ECMWF solution that shows
weakening.


FORECAST POSITIONS AND MAX WINDS

INIT  19/2100Z 11.5N  42.0W   45 KT  50 MPH
 12H  20/0600Z 12.1N  43.2W   50 KT  60 MPH
 24H  20/1800Z 12.6N  44.8W   55 KT  65 MPH
 36H  21/0600Z 13.1N  46.3W   60 KT  70 MPH
 48H  21/1800Z 13.8N  47.9W   65 KT  75 MPH
 72H  22/1800Z 15.0N  51.8W   75 KT  85 MPH
 96H  23/1800Z 16.0N  56.9W   70 KT  80 MPH
120H  24/1800Z 16.8N  62.0W   60 KT  70 MPH

$$
Forecaster Kimberlain

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