[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT45 KNHC 011459
TCDAT5

Tropical Depression Kate Discussion Number  18
NWS National Hurricane Center Miami FL       AL102021
1100 AM AST Wed Sep 01 2021

It has been difficult to pinpoint where the low-level circulation of
Kate is this morning. After last night's diurnal convective maximum,
the remaining convection has taken on a very disorganized structure,
with a mid-level vortex being left behind to the south, while
deeper, but more outflow driven convection is racing off to the
north, ahead of the estimated low-level center position. A recently
received 1211 UTC ASCAT-A pass indicated that Kate's low-level
circulation is still closed, but just barely. The scatterometer wind
data supports maintaining the current intensity at 30-kt, which also
agrees with the latest subjective and objective Dvorak estimates.

The estimated motion is continuing off to the north-northwest, at
340/9 kt. Kate appears to now be primarily steered by the low-level
flow around a subtropical ridge located to its east. A general
north-northwest motion is expected to continue today, followed by a
turn to the north and north-northeast around the periphery of this
ridge. The latest NHC track guidance has been adjusted a bit right
of the previous track, shifting towards the latest consensus
guidance (TVCN) that can still track the cyclone beyond 24 hours.

A 0958 UTC SSMIS microwave pass suggested that the better organized
structure observed last night has decayed, with the low- and
mid-level centers quite misaligned. Vertical wind shear diagnosed by
SHIPS is now between 15-20 kt out of the north. This shear is likely
contributing to the vortex tilt, while also helping to import very
dry mid-level air, preventing Kate's convective activity from
organizing.  The bulk of the intensity guidance is in agreement that
gradual spin down of the low-level circulation will occur over the
next several days, with the deterministic ECMWF model suggesting
Kate could open up to a trough as soon as tomorrow. The latest NHC
intensity forecast makes Kate a remnant low in 36 hours, with
dissipation after 48 hours. However, given the current structure,
this could occur sooner than forecast.


FORECAST POSITIONS AND MAX WINDS

INIT  01/1500Z 26.8N  52.3W   30 KT  35 MPH
 12H  02/0000Z 27.9N  52.7W   25 KT  30 MPH
 24H  02/1200Z 29.6N  53.1W   25 KT  30 MPH
 36H  03/0000Z 31.1N  53.2W   20 KT  25 MPH...POST-TROP/REMNT LOW
 48H  03/1200Z 32.4N  52.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
 60H  04/0000Z...DISSIPATED

$$
Forecaster Papin
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