[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT41 KNHC 190849
TCDAT1

Tropical Storm Peter Discussion Number   2
NWS National Hurricane Center Miami FL       AL162021
500 AM AST Sun Sep 19 2021

Deep convection has increased since the previous advisory, with the
convective cloud pattern having taken on a more curved-band
configuration compared to the earlier shear pattern. Satellite
intensity estimates from TAFB and SAB support increasing the
intensity to 35 kt. In addition, earlier ASCAT passes, which missed
the center of circulation, did reveal 30-kt winds west of the center
in convection-free areas. Thus, it is reasonable to assume that
stronger winds are occurring within the deep convection east of the
center, which further supports upgrading the system to Tropical
Storm Peter with a 35-kt intensity.

The initial estimate is an uncertain 305/13 kt. Peter has made a
slight jog to the north-northwest since the previous advisory, but
this is likely a short-term motion owing to the center redeveloping
farther to the north and east into the deep convection. However, a
west-northwestward motion is expected to resume later today.
Thereafter, the cyclone is forecast to maintain a west-northwestward
motion through Wednesday as Peter moves around the southwestern
periphery of a strong deep-layer subtropical ridge. On Thursday and
Friday, Peter is forecast to turn northward into a weakness in the
ridge induced by the large Post-Tropical Cyclone Odette.  The new
forecast track has been shifted slightly to the right or north of
the previous advisory track, mainly due to the more northward
initial position, and lies close to the consensus track models TVCA
and HCCA.

Some strengthening is forecast during the next 24 hours or so as
Peter moves over warmer sea-surface temperatures of about 29 deg C.
However, proximity to very dry mid-level air and moderate
deep-layer southwesterly vertical wind shear are expected to prevent
any significant or rapid strengthening. By early Tuesday and
beyond, slow weakening is expected to begin due to increasing wind
shear.  The new official NHC intensity forecast is very similar to
the previous advisory, and closely follows a blend of the IVCN and
HCCA intensity consensus models.

Based on the track, intensity, and wind radii forecast, no tropical
storm watches or warnings are required for the northern Leeward
Islands, Virgin Islands or Puerto Rico.  However, interests there
should monitor the progress of the system as locally heavy rain is
possible on Monday and Tuesday when it is expected to pass to the
north of the area.

Key Messages:

1. Rainfall around the southern periphery of Tropical Storm Peter
may lead to areas of urban and small stream flooding from late
Sunday into Tuesday across Puerto Rico, the Virgin Islands, and the
Northern Leeward Islands.

FORECAST POSITIONS AND MAX WINDS

INIT  19/0900Z 18.0N  53.5W   35 KT  40 MPH
 12H  19/1800Z 18.8N  55.3W   40 KT  45 MPH
 24H  20/0600Z 19.8N  57.8W   40 KT  45 MPH
 36H  20/1800Z 20.8N  60.1W   40 KT  45 MPH
 48H  21/0600Z 21.7N  62.2W   35 KT  40 MPH
 60H  21/1800Z 22.7N  63.9W   35 KT  40 MPH
 72H  22/0600Z 23.7N  64.9W   35 KT  40 MPH
 96H  23/0600Z 25.8N  65.6W   35 KT  40 MPH
120H  24/0600Z 27.7N  65.2W   35 KT  40 MPH

$$
Forecaster Stewart
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