Remnants of Fifteen Forecast Discussion


000
WTNT45 KNHC 160833
TCDAT5

Remnants Of Fifteen Discussion Number   7
NWS National Hurricane Center Miami FL       AL152019
500 AM AST Wed Oct 16 2019

Satellite images indicate that the surface circulation of the
system has become rather elongated north-to-south, with only a few
weak swirls in the circulation envelope, and has degenerated into a
trough of low pressure.  Thus it is no longer a tropical cyclone,
and this is the last advisory.  The winds are lowered to 25 kt,
matching the TAFB classification.

The remnants of the cyclone are expected to move northwestward
during the next few days.  There is a slight chance of
regeneration, as suggested by the ECMWF model and some of its
ensemble members due to a trough interaction, but that's considered
unlikely at this point.


FORECAST POSITIONS AND MAX WINDS

INIT  16/0900Z 17.3N  24.1W   25 KT  30 MPH
 12H  16/1800Z...DISSIPATED

$$
Forecaster Blake

Tropical Depression Fifteen Forecast Discussion


000
WTNT45 KNHC 160235
TCDAT5

Tropical Depression Fifteen Discussion Number   6
NWS National Hurricane Center Miami FL       AL152019
1100 PM AST Tue Oct 15 2019

The tropical depression located near the Cabo Verde Islands has
become less organized over the past 6 hours. An ASCAT-A overpass at
2154 UTC showed that the depression still had a closed and
well-defined center, but the strongest winds were only 20-25 kt. A
subsequent ASCAT-B pass about 1 hour later showed slightly higher
winds but an elongated circulation. Furthermore, deep convection is
limited to a small area of showers located nearly 100 n mi to the
east of the depression's center. If its convection continues to
decrease, the system could become a remnant low later today.
Alternatively, if its circulation continues to become elongated, it
could soon open into a trough and dissipate. Either way, it seems
unlikely that the depression will remain a tropical cyclone for
long, and this shown by all of the models and the official forecast.

The depression has made a westward jog since the last advisory, but
a longer-term motion estimate is 300/09 kt. The westward jog
resulted in a substantial westward shift in the official forecast
track, but the system is still expected to move generally
west-northwestward to northwestward for the next day or two until it
dissipates. The track guidance is in good agreement on this
scenario, and the main source of uncertainty is just how quickly the
system will open into a trough.

The latest ECMWF deterministic forecast and few of its ensemble
members indicate that the cyclone could regenerate later this week.
However, most other models do not forecast regeneration and the
uncertainty is too high to justify explicitly showing this in the
official forecast.


FORECAST POSITIONS AND MAX WINDS

INIT  16/0300Z 16.8N  23.7W   30 KT  35 MPH
 12H  16/1200Z 17.7N  24.6W   30 KT  35 MPH
 24H  17/0000Z 18.6N  25.7W   25 KT  30 MPH...POST-TROP/REMNT LOW
 36H  17/1200Z 19.6N  27.2W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  18/0000Z 20.8N  29.3W   20 KT  25 MPH...POST-TROP/REMNT LOW
 72H  19/0000Z...DISSIPATED

$$
Forecaster Zelinsky

Tropical Depression Fifteen Forecast Discussion


000
WTNT45 KNHC 142040
TCDAT5

Tropical Depression Fifteen Discussion Number   1
NWS National Hurricane Center Miami FL       AL152019
500 PM AST Mon Oct 14 2019

The large low pressure system that moved off the coast of Africa
yesterday has gradually become better defined based on earlier ASCAT
scatterometer wind data and recent visible satellite imagery.
Several fragmented curved bands have been developing during the past
several hours, especially in the northern semicircle, and the
aforementioned ASCAT passes indicated that winds of 30-32 kt were
present northwest of the center. The initial intensity is set at 30
kt based on a blend of the scatterometer wind data and a satellite
intensity estimate of T1.5/25 kt from SAB, and the rather broad
nature of the depression.

A surge of mid-level dry air has recently penetrated into the
inner-core region, causing some erosion of the central deep
convection. However, this is expected to be a temporary condition
with convection returning later tonight and early Tuesday during the
normal nocturnal convective maximum period. However, the large size
of the cyclone -- more than 1000 nmi wide -- should prevent any
rapid or significant intensification. With very low vertical shear
conditions forecast by the GFS and ECMWF models to continue for the
next 24 to 36 hours, at least some modest strengthening seems likely
given the unusually warm SSTs of near 28.5 deg C that the cyclone
will be traversing during that time. By 48 hours, the shear is
forecast to increase from the southwest in excess of 25 kt,
resulting in weakening into a remnant low shortly thereafter. By 72
hours and beyond, the shear is expected to increase to more than 40
kt, which will cause rapid weakening and dissipation by the 120-h
period, if not sooner. The official intensity forecast is similar to
a blend of the NOAA-HCCA and IVCN consensus models, and the GFS-
and ECMWF-based Decay-SHIPS statistical intensity models.

The initial motion estimate is northwestward or 310/07 kt. The
latest NHC model guidance is in very good agreement on the tropical
cyclone moving generally northwestward around the southwestern
periphery of a deep-layer ridge for the next 48 hours. Thereafter,
the models diverge significantly based on how soon the cyclone
weakens and turns westward within the low-level easterly trade wind
flow. The ECMWF holds on to a vertically deeper system a little
longer than the GFS, UKMET, HWRF, and HMON models, resulting in a
longer northwestward track. However, since the cyclone will likely
have become a vertically shallow remnant low by 72 hours, the NHC
official forecast track is a little to the left of ECMWF solution,
closer to the TVCN and HCCA consensus model tracks at 72 and 96 h.

FORECAST POSITIONS AND MAX WINDS

INIT  14/2100Z 13.2N  20.2W   30 KT  35 MPH
 12H  15/0600Z 14.3N  21.1W   35 KT  40 MPH
 24H  15/1800Z 15.5N  22.4W   40 KT  45 MPH
 36H  16/0600Z 16.7N  23.4W   40 KT  45 MPH
 48H  16/1800Z 18.1N  24.6W   35 KT  40 MPH
 72H  17/1800Z 20.4N  26.9W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  18/1800Z 21.4N  29.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  19/1800Z...DISSIPATED

$$
Forecaster Stewart

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