3. A non-tropical area of low pressure is located over the far
northeastern Atlantic Ocean several hundred miles northeast of the
Azores. This system is forecast to move south-southeastward during
the next few days where it will encounter warmer waters, which
could allow the low to gradually acquire some tropical or
subtropical characteristics this week.
* Formation chance through 48 hours...low...10 percent.
* Formation chance through 5 days...low...20 percent.
NHC will initiate advisories on Subtropical Storm Alpha, located near the coast of Portugal, at 1230 PM AST (1630 UTC).
WTNT44 KNHC 181634
TCDAT4
Subtropical Storm Alpha Special Discussion Number 1
NWS National Hurricane Center Miami FL AL242020
430 PM GMT Fri Sep 18 2020
The small low pressure area that has been rotating around a larger
extratropical low in the far northeastern Atlantic has become better
organized this morning. Moderate-to-deep convection has persisted
near the center since last night, scatterometer data shows a closed
40-kt low, and radar images from Portugal show a definite organized
convective pattern. While the system is still in the cyclonic
envelope of the large extratropical low and likely neutral- or
cold-core, it has developed enough tropical characteristics to be
considered a subtropical storm. The initial intensity is set to 45
kt in accordance with the scatterometer data, assuming some
undersampling for this small system.
Little change in strength is forecast until landfall in Portugal
during the next couple of hours. Global models show the small low
moving northeastward at about 15 kt for the next 24 hours before
dissipating over northern Spain or the Bay of Biscay. The track and
intensity forecasts are consistent with the consensus guidance.
Additional information on the hazards from this system can be found
in products from the Portuguese Institute for Sea and Atmosphere at www.ipma.pt.
Post-Tropical Cyclone Alpha Discussion Number 3
NWS National Hurricane Center Miami FL AL242020
300 AM GMT Sat Sep 19 2020
METEOSAT imagery, IPMA radar data, and surface observations
indicate that Alpha has degenerated to a post-tropical remnant low
just a few miles to the southeast of Viseu, Portugal. Therefore,
this the last NHC advisory. Surface wind data support an initial
intensity of 25 kt. The rapidly deteriorating small remnant low is
expected to move generally toward the northeast at about 14 kt for
the next 6 to 12 hours before dissipating over northern Spain by
Saturday night. The NHC forecast track is basically an update of
the previous advisory and lies between the tightly clustered
deterministic guidance.
Additional information on the hazards from this system can be found
in products from the Portuguese Institute for Sea and Atmosphere at www.ipma.pt.
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