Tropical Storm Alpha

Subtropical Storm Alpha Track 2100 Hours Sepember 18 2020
Subtropical Storm Alpha Track 2100 Hours Sepember 18 2020

Tropical Storm Alpha Wind Speed FieldTropical Storm Alpha – NWS National Hurricane Center Miami FL 900 PM GMT Fri Sep 18, 2020 (see video below)

Radar data from Portugal indicated that Alpha made landfall at about 1830 UTC with a fairly impressive spiral band signature. It is estimated that the winds were 45 kt at landfall, and a sustained 10-minute wind of 39 kt was recorded at Sao Pedro de Noel. The minimum central pressure is analyzed at 996 mb at landfall due to a 999 mb value at Monte Real with a 31-kt sustained wind. Since these data were recorded, the radar presentation has deteriorated, and satellite imagery suggests the small cyclone could be de-coupling from its mid-level center. The winds are assumed to have come down, with a current estimate of 40 kt. The small cyclone should continue to move northeastward at about 15 kt for the next 12-24 hours before dissipating over northern Spain or the Bay of Biscay.

No significant changes are required to the forecast for track or intensity.

FORECAST POSITIONS AND MAX WINDS

INIT  18/2100Z 40.4N   8.4W   40 KT  45 MPH - Tropical Storm (ESE VN de Monsarros, Portugal)
 12H  19/0600Z 42.1N   6.1W   25 KT  30 MPH - Post Tropical (ESE  Congosta, Spain)
 24H  19/1800Z...DISSIPATED

NWS National Hurricane Center Miami FL 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.

FORECAST POSITIONS AND MAX WINDS

INIT  18/1630Z 39.9N   9.3W   45 KT  50 MPH - Tropical Storm (WSW Vieira de Leiria, Portugal)
 12H  19/0000Z 41.5N   7.5W   30 KT  35 MPH - Depression (WSW Curros, Portugal)
 24H  19/1200Z 44.2N   4.2W   30 KT  35 MPH - Low (WNW Santander, Spain)
 36H  20/0000Z...DISSIPATED

NWS National Hurricane Center Miami FL 200 AM EDT Fri Sep 18, 2020

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Hurricane Teddy, located over the central tropical Atlantic, and on Tropical Depression Twenty-Two, located over the southwestern Gulf of Mexico.

  • 1. Showers and thunderstorms associated with an area of low pressure located a few hundred miles southwest of the Cabo Verde Islands have increased during the past several hours. Earlier satellite-derived wind data indicated that this system does not yet have a well-defined center, but it is producing winds near tropical-storm-force to its east. Environmental conditions are expected to be conducive for additional development during the next day or two and a tropical depression or tropical storm could form before the end of the week. This system is forecast move west-northwestward at 10 to 15 mph through the weekend. * Formation chance through 48 hours…medium…60 percent. * Formation chance through 5 days…medium…60 percent.
  • 2. A small low-pressure system is embedded within a larger non-tropical low. Although showers and thunderstorms associated with the smaller low are showing signs of organization, the system will soon move inland over Portugal and further tropical or subtropical development is unlikely. The low is producing gale-force winds, and will likely bring gusty winds and brief periods of heavy rain to portions of western Portugal today and tonight. For more information about potential hazards in Portugal, please see products issued by the Portuguese Institute for the Sea and the Atmosphere (IPMA). For more information about marine hazards associated with this system, see High Seas Forecasts issued by Meteo France. * Formation chance through 48 hours…low…20 percent. * Formation chance through 5 days…low…20 percent.
  • 3. Post-tropical cyclone Paulette is located several hundred miles north-northwest of the Azores. The cyclone is forecast to move quickly southward for the next several days and then stall over marginally warm waters a few hundred miles south or south-southwest of the Azores by the end of the weekend. The cyclone could subsequently redevelop tropical characteristics late this weekend or early next week while it moves little. * Formation chance through 48 hours…low…10 percent. * Formation chance through 5 days…low…20 percent. 4. Another tropical wave is forecast to move off the west coast of Africa by early Saturday. Some gradual development of the system will be possible thereafter while it moves generally west-northwestward over the far eastern Atlantic. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low…20 percent.

NWS National Hurricane Center Miami FL 200 PM EDT Thu Sep 17, 2020

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Hurricane Teddy, located over the central tropical Atlantic and on recently downgraded Tropical Depression Vicky, located over the eastern tropical Atlantic.

  • 1. Shower and thunderstorm activity has changed little today in association with an area low pressure system located over the southwestern Gulf of Mexico. Upper-level winds are gradually becoming more conducive for development, and a tropical depression or a tropical storm could form within the next day or so. The low is expected to meander over the southwestern Gulf of Mexico through tonight before moving slowly northward to northeastward on Friday and Saturday. An Air Force Reserve reconnaissance aircraft is scheduled to investigate the disturbance this afternoon. For more information on this system, see High Seas Forecasts issued by the National Weather Service. * Formation chance through 48 hours…high…90 percent. * Formation chance through 5 days…high…90 percent. [Wilfred]
  • 2. An elongated area of low pressure located a few hundred miles south-southwest of the Cabo Verde Islands is producing disorganized shower and thunderstorm activity. Environmental conditions are expected to be conducive for development during the next few days, and a tropical depression could form before upper-level winds become less favorable by late this weekend. The system is forecast to move west-northwestward at 10 to 15 mph during the next several days. * Formation chance through 48 hours…medium…40 percent. * Formation chance through 5 days…medium…50 percent.
  • 3. Showers and thunderstorms have change little since this morning in association with a non-tropical area of low pressure located over the far northeastern Atlantic Ocean several hundred miles east of the Azores. Some additional subtropical development is possible over the next day or so as it moves east-southeastward and then northeastward at about 10 mph. The system is expected to reach the coast of Portugal late Friday. For more information on this system, see High Seas Forecasts issued by Meteo France. * Formation chance through 48 hours…low…30 percent. * Formation chance through 5 days…low…30 percent.

If this system is named, it will become Tropical Storm Alpha.

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Video: Tropical Storm Wilfred Forms in Atlantic, Future Storms to be Named After Greek Alphabet