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Tropical Depression TWENTY-ONE-E


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TROPICAL DEPRESSION TWENTY-ONE-E DISCUSSION NUMBER   3
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP212015
800 PM MST WED NOV 18 2015

The depression is poorly organized with the low-level center well
separated from the mid-level circulation as indicated by several
microwave images. Similar to earlier today, the low-level center
continues to be located to the southeast of the weakening
convection, indicating that southeasterly shear still prevails.
Initial intensity remains at 30 kt based on satellite estimates from
TAFB and SAB.

There is an opportunity for the depression to strengthen slightly
during the next day or two, while a narrow ridge builds to the
north of the cyclone and the shear decreases. Most of the intensity
models forecast some increase in the winds, and so does the NHC
forecast. In fact, the NHC forecast still brings the depression to
tropical storm status in about 12 to 24 hours. However, by the end
of the forecast period, the effects of cooler waters and dry air
should result in weakening.

The center has moved very little during the past several hours, or
perhaps it has has been drifting eastward and then northward around
a larger cyclonic gyre. Most of the global models build a ridge to
the north of the cyclone soon, and this steering pattern should
force the depression to begin to move on a west-northwest track
early Thursday. It should then continue with this general motion for
the next 2 to 3 days. After that time, a new mid-latitude trough is
forecast to approach from the west, weakening the ridge and inducing
a northward motion. However, there is little confidence in the track
forecast by the end of the period due to large spread in the model
tracks. The NHC forecast follows closely the multi-model consensus,
and is a little to the east of the previous NHC forecast beyond 3
days.

FORECAST POSITIONS AND MAX WINDS

INIT  19/0300Z 13.2N 106.1W   30 KT  35 MPH
 12H  19/1200Z 13.7N 106.5W   35 KT  40 MPH
 24H  20/0000Z 14.6N 108.2W   40 KT  45 MPH
 36H  20/1200Z 15.5N 110.0W   45 KT  50 MPH
 48H  21/0000Z 16.0N 111.0W   45 KT  50 MPH
 72H  22/0000Z 17.5N 113.0W   40 KT  45 MPH
 96H  23/0000Z 19.0N 114.0W   30 KT  35 MPH
120H  24/0000Z 21.0N 114.0W   20 KT  25 MPH...POST-TROP/REMNT LOW

$$
Forecaster Avila

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