Tropical Storm Teresa

Post Tropical Storm Teresa Track 1700 Hours September 25 2021
Post Tropical Storm Teresa Track 1700 Hours September 25 2021

Tropical Storm Teresa Wind Speed FieldTropical Storm Teresa NWS National Hurricane Center Miami FL 500 PM AST Sat Sep 25, 2021 (see Saturday video below)

Teresa has continued to consist of just a swirl of low-level clouds since last night. Although a convective band persists a couple hundred miles northeast of the low center, the system no longer meets the definition of a tropical cyclone. Strong west-southwesterly wind shear should prevent any regeneration of convection near the center. All of the global models show the remnant low degenerating into an open trough by Sunday morning.

Teresa has been moving eastward or 090/4 kt during the past 12 hours. A turn to the northeast is expected within the next couple of hours as the cyclone moves in the southwesterly flow ahead of a deep-layer trough. The northeastward motion should continue until the low dissipates Sunday morning.

This is the final update.

FORECAST POSITIONS AND MAX WINDS

INIT  25/2100Z 34.4N  64.3W   30 KT  35 MPH - Post Tropical (ENE St. George's,Bermuda)
 12H  26/0600Z 35.7N  63.2W   30 KT  35 MPH - Post Tropical (ENE St. George's,Bermuda)

NWS National Hurricane Center Miami FL 1100 AM AST Sat Sep 25, 2021

Teresa has been devoid of deep convection for more than 12 hours now. The cloud pattern consists of a swirl of low-level clouds and a band of showers and thunderstorms located about 250 n mi north of the center. This patch of convection is detached from the low-level circulation, and it appears to be more involved with an upper-level trough to the northeast of Teresa. A 1210 UTC ASCAT-A pass shows that the winds within that convection have decreased, with several vectors in the 25 to 30 kt range. Based on that data, the intensity is lowered to 30 kt, making Teresa a subtropical depression.

Teresa is unlikely to redevelop any convection near its center as strong west-southwesterly wind shear continues over the cyclone. This will prevent any opportunity for strengthening. Teresa is expected to become a remnant low later today or this evening and dissipate on Sunday. The global models are in good agreement with this scenario.

Teresa has moved little during the past 12 hours, so a stationary motion is currently indicated for this advisory. However, a motion toward the northeast should begin within the next few hours and continue through dissipation as the cyclone moves in the flow ahead of a deep-layer trough. The track forecast was adjusted a little to the east of the previous advisory, and is in agreement with the model consensus.

FORECAST POSITIONS AND MAX WINDS

INIT  25/1500Z 34.3N  65.0W   30 KT  35 MPH - Depression (ENE St. George's,Bermuda)
 12H  26/0000Z 35.4N  64.4W   30 KT  35 MPH - Post Tropical (ENE St. George's,Bermuda)
 24H  26/1200Z 37.2N  62.6W   30 KT  35 MPH - Post Tropical (ENE St. George's,Bermuda)
 36H  27/0000Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 PM AST Fri Sep 24, 2021

Teresa’s cloud pattern is not well organized, even for a subtropical cyclone. The main convective band is rather ragged in appearance, and situated 100 n mi or more to the east and northeast of the exposed low-level center. The current intensity estimate, 40 kt, is in general agreement with the latest subtropical satellite classification from TAFB, but given the disheveled appearance of the system, this may be generous.

Teresa has recently been moving more westward than northward, on the northern side of a mid-level cyclonic circulation, and the current motion estimate is an uncertain 300/9 kt. During the next day or so, the cyclone is likely to turn northward and northeastward ahead of a mid-tropospheric trough that will be moving over the northeastern United States and Atlantic Canada. The official forecast is a little faster than the previous one, but along the same general trajectory. The HCCA model consensus is somewhat faster than the NHC prediction.

The cyclone has been situated under an upper-level low which has kept the vertical shear fairly low thus far. However, as this low moves away from the area, Teresa will begin to experience increasing west-southwesterly shear, and no strengthening is expected. In 48 hours or so, based on the global models, the storm is forecast to become absorbed by the aforementioned trough.

FORECAST POSITIONS AND MAX WINDS

INIT  25/0300Z 34.3N  65.4W   40 KT  45 MPH - Tropical Storm (ENE St. George's,Bermuda)
 12H  25/1200Z 35.2N  65.5W   40 KT  45 MPH - Tropical Storm (ENE St. George's,Bermuda)
 24H  26/0000Z 36.2N  64.9W   40 KT  45 MPH - Tropical Storm (ENE St. George's,Bermuda)
 36H  26/1200Z 37.8N  64.0W   40 KT  45 MPH - Tropical Storm (ENE St. George's,Bermuda)
 48H  27/0000Z...ABSORBED

NWS National Hurricane Center Miami FL 500 PM AST Fri Sep 24, 2021 

The disturbance just north of Bermuda interacting with a mid- to upper-level low has developed a prominent band of deep convection within its eastern semicircle as well as a well-defined surface center. Additionally, the system is not displaying any significant baroclinicity (i.e., frontal boundaries), so it is not an extratropical cyclone. All of which indicates that the system has evolved into a subtropical cyclone. ASCAT-C scatterometer data from 1440Z suggested peak winds were around 40 kt, which is the basis for calling the system Subtropical Storm Teresa.

The system is moving toward the northwest at 12 kt is it rounds the northern part of the mid- to upper-level low. By Saturday, Teresa should turn northward and then northeastward, as it begins to be caught up in the mid-latitude westerlies. The forecast is based upon the TVCN track consensus technique.

Teresa will not be long-lived. A developing extratropical system forming off of New England should absorb Teresa between 36 and 48 hours. Until then, the subtropical storm has a small window to intensify slightly while traversing lukewarm water and encountering moderate vertical shear. If deep convection develops near the system’s center, then Teresa could evolve into a tropical storm. However, it is more likely that Teresa will remain a subtropical storm until dissipation in around two days.

It is worth noting that Teresa will likely be the 9th so-called “shortie” of the 2021 hurricane season — systems that are short- lived and relatively weak.

FORECAST POSITIONS AND MAX WINDS

INIT  24/2100Z 34.5N  64.5W   40 KT  45 MPH - Tropical Storm (ENE St. George's,Bermuda)
 12H  25/0600Z 35.4N  65.5W   45 KT  50 MPH - Tropical Storm (ENE St. George's,Bermuda)
 24H  25/1800Z 36.3N  65.5W   45 KT  50 MPH - Tropical Storm (ENE St. George's,Bermuda)
 36H  26/0600Z 37.2N  64.4W   40 KT  45 MPH - Tropical Storm (ENE St. George's,Bermuda)
 48H  26/1800Z...DISSIPATED

NWS National Hurricane Center Miami FL 800 AM EDT Fri Sep 24, 2021

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

The National Hurricane Center is issuing advisories on recently upgraded Hurricane Sam, located about 1400 miles east-southeast of the northern Leeward Islands.

  • 1. A large area of showers and thunderstorms centered a couple hundred miles east of Bermuda is associated with a formative surface low interacting with an upper-level trough. Additional tropical or subtropical development of this system could occur through early Saturday as it moves generally north-northwestward. After that time, development is not expected due to strong upper-level winds. Additional information on this system, including gale warnings, can be found in High Seas Forecasts issued by the National Weather Service. * Formation chance through 48 hours…medium…40 percent. * Formation chance through 5 days…medium…40 percent.
  • 2. A gale-force, non-tropical low pressure system, the remnants of Odette, is located a little less than 600 miles west-northwest of the westernmost Azores. Showers and thunderstorms remain limited near the low, and the window of opportunity for this system to become a subtropical or tropical cyclone is closing as strong upper-level winds are expected to develop over the system later today. This system will move generally south-southeastward over the next day or two. Additional information on this system, including gale warnings, can be found in High Seas Forecasts issued by the National Weather Service. * Formation chance through 48 hours…low…20 percent. * Formation chance through 5 days…low...20 percent.
  • 3. A tropical wave is expected to move off the west coast of Africa by the end of this weekend. Thereafter, environmental conditions are forecast to be conducive for gradual development, and a tropical depression could form by the middle of next week while the system moves westward at 10 to 15 mph over the far eastern tropical Atlantic. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…medium…40 percent.

NWS National Hurricane Center Miami FL 800 PM EDT Thu Sep 23, 2021

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

The National Hurricane Center is issuing advisories on Tropical Storm Sam, located about 1600 miles east-southeast of the northern Leeward Islands.

  • 1. A gale-force, non-tropical low pressure system, the remnants of Odette, is located a little more than 600 miles west-northwest of the westernmost Azores. Showers and thunderstorms remain limited near the low, and this system has only a brief window of opportunity to become a subtropical or tropical cyclone while it moves generally south-southeastward over marginally warmer waters during the next day or so. Strong upper-level winds are expected to develop over the system beginning tomorrow, which should then limit further development. Additional information on this system, including gale warnings, can be found in High Seas Forecasts issued by the National Weather Service. * Formation chance through 48 hours…medium…50 percent. * Formation chance through 5 days…medium…50 percent.
  • 2. A large area of showers and thunderstorms located a few hundred miles southeast of Bermuda is associated with a surface and upper-level trough. Some tropical or subtropical development of this system could occur in the next day or two as it moves generally north-northwestward. Strong upper-level winds should prohibit further development by this weekend. * Formation chance through 48 hours…low…10 percent. * Formation chance through 5 days…low...10 percent.
  • 3. A tropical wave is expected to move off the west coast of Africa by the end of this weekend. Thereafter, environmental conditions are forecast to be conducive for gradual development of this system as it moves westward at 10 to 15 mph over the far eastern tropical Atlantic. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low...30 percent.

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Video: Tracking the Tropics: Hurricane Sam continues to strength in Atlantic