Skip Navigation Links
NOAA NOAA United States Department of Commerce

Tropical Storm IDA


ZCZC MIATCDAT5 ALL
TTAA00 KNHC DDHHMM

TROPICAL STORM IDA DISCUSSION NUMBER  13
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL102015
1100 AM AST MON SEP 21 2015

Ida has been producing a large cluster of very deep convection
overnight and this morning.  The tropical cyclone, however, is still
being affected by shear as the low-level center can be seen in
visible satellite imagery just northwest of the convection, and this
was confirmed by a recent scatterometer pass. The initial wind speed
is maintained at 45 kt, which is based on the latest TAFB Dvorak
T-number and the recent ASCAT data that revealed winds of around
40 kt.

The upper-level wind pattern is forecast to become a little more
conducive for strengthening during the next 12 to 24 hours and the
NHC forecast calls for some slight intensification.  After that
time, northwesterly shear is expected to increase as an upper-level
trough to the northeast of Ida retrogrades westward.  This could
cause some weakening, but most of the intensity guidance shows
little change in strength during this time, and the NHC forecast
maintains an intensity of 55 kt from 24 to 72 hours.  Later in the
forecast period, the global models take the upper-level trough
northeastward and develop a more favorable upper-air pattern over
the tropical cyclone, which should allow for strengthening by
days 4 and 5.  The new NHC intensity forecast is similar to the
previous advisory, and is close to the SHIPS and LGEM
models.

The forward motion of Ida continues to decrease and is now 330/6
kt.  The steering currents around the tropical cyclone are forecast
to further weaken during the next day or so as the mid- to
upper-level trough retrogrades westward.  Ida should become
nearly stationary tonight, then meander eastward or east-
southeastward on Tuesday and Wednesday as the mid- to upper-level
flow becomes northwestward.  The dynamical models have come into
better agreement on this scenario, including the latest GFS run
that shifted eastward and is now close to the ECMWF.  After 72
hours, when the trough moves northeastward, Ida should turn
northwestward at a faster forward speed.  The updated NHC
track has been adjusted eastward and is close to a blend of the
ECMWF, GFS, and GFS ensemble mean.


FORECAST POSITIONS AND MAX WINDS

INIT  21/1500Z 20.6N  48.0W   45 KT  50 MPH
 12H  22/0000Z 21.1N  48.1W   50 KT  60 MPH
 24H  22/1200Z 21.3N  47.7W   55 KT  65 MPH
 36H  23/0000Z 21.2N  47.3W   55 KT  65 MPH
 48H  23/1200Z 20.7N  46.7W   55 KT  65 MPH
 72H  24/1200Z 20.8N  46.1W   55 KT  65 MPH
 96H  25/1200Z 22.0N  46.8W   60 KT  70 MPH
120H  26/1200Z 24.0N  48.0W   65 KT  75 MPH

$$
Forecaster Brown

NNNN