[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 090844
TCDAT5

Tropical Storm Elsa Discussion Number  37
NWS National Hurricane Center Miami FL       AL052021
500 AM EDT Fri Jul 09 2021

Elsa has become better organized this early Friday morning as
evidenced by a tightly coiled convective band that wraps completely
around the low-level circulation center, along with Doppler radar
velocities of more than 80 kt detected between 3000-7000 ft.
Upper-level outflow has expanded in all directions except the
southwestern quadrant, and the GFS and ECMWF models have assessed
the vertical wind shear to only be 10 kt and 13 kt, respectively,
over the center. Wind gusts to 68 kt and 62 kt were recently
measured in Ludlam Bay, New Jersey, and Beach Haven, New Jersey,
respectively. However, radar data suggest that these wind gusts were
possibly associated with the passage of nearby tornadic circulations
and were not due to Elsa's larger wind field. The central pressure
of 1000 mb is based on a nearby pressure report of 1000.6 mb from
the Ludlam Bay, New Jersey, WeatherFlow site, but this value could
be conservative. The initial wind speed remains 45 kt based on
recent observations from offshore buoys.

The initial motion is estimated to be 045/27 kt. Elsa is forecast
by the latest global and regional models to continue accelerating
northeastward today through Saturday due to the system being
embedded within deep-layer southwesterly mid-latitude flow. Elsa
should move over southeastern New England today and over Atlantic
Canada late tonight and on Saturday. The new NHC track forecast lies
on top of the previous advisory track and is close to the middle of
the tightly packed simple- and corrected-consensus track models.

Elsa will be moving over 22-deg-C and cooler sea-surface
temperatures by 6 hours and beyond, which should further hasten
the ongoing extratropical transition process. This transition is
expected to be completed in 18 hours or so when Elsa is forecast to
be located over Atlantic Canada.

Key Messages:

1. As Elsa moves near Long Island and southern and coastal New
England today, heavy rainfall could lead to considerable flash
and urban flooding.

2. Tropical storm conditions should continue along portions of the
mid-Atlantic coast early this morning. Tropical storm conditions
are expected in portions of the southern New England states and New
York by late this morning and afternoon.  Gusty winds are expected
over portions of Atlantic Canada tonight and Saturday.


FORECAST POSITIONS AND MAX WINDS

INIT  09/0900Z 39.4N  74.3W   45 KT  50 MPH...OVER WATER
 12H  09/1800Z 42.2N  70.3W   45 KT  50 MPH...OVER WATER
 24H  10/0600Z 46.6N  63.4W   45 KT  50 MPH...POST-TROP/EXTRATROP
 36H  10/1800Z 51.3N  54.5W   40 KT  45 MPH...POST-TROP/EXTRATROP
 48H  11/0600Z 55.4N  45.2W   35 KT  40 MPH...POST-TROP/EXTRATROP
 60H  11/1800Z 59.5N  36.0W   30 KT  35 MPH...POST-TROP/EXTRATROP
 72H  12/0600Z...DISSIPATED

$$
Forecaster Stewart
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