Tropical Storm Theta

Post Tropical Storm Theta Track 1500 Hours November 15 2020
Post Tropical Storm Theta Track 1500 Hours November 15 2020

Tropical Storm Theta Wind Speed FieldTropical Storm ThetaNWS National Hurricane Center Miami FL 300 PM GMT Sun Nov 15, 2020 (see Sunday video below)

Theta has run out of theta-e. The cyclone has been without significant deep convection for many hours now and has been gradually spinning down today. It no longer meets the qualifications of a tropical cyclone, so this is the last advisory. The initial wind speed is set to 25 kt per the latest scatterometer pass.

The low is meandering this morning. It is expected to be picked up to the north-northeast by the next trough over the northeastern Atlantic, along with an increase in forward speed. The remnants of Theta should gradually lose strength due to strong shear, very dry air and little instability before dissipating in a day or two.

FORECAST POSITIONS AND MAX WINDS

INIT  15/1500Z 31.5N  18.2W   25 KT  30 MPH - Post Tropical ()
 12H  16/0000Z 31.9N  18.1W   25 KT  30 MPH - Low ()
 24H  16/1200Z 33.7N  17.7W   20 KT  25 MPH - Low ()
 36H  17/0000Z 36.5N  16.5W   20 KT  25 MPH - Low ()
 48H  17/1200Z...DISSIPATED

NWS National Hurricane Center Miami FL 300 AM GMT Sun Nov 15, 2020 

Theta remains a highly sheared but resilient tropical cyclone with little change in its satellite appearance since the previous advisory. A persistent band of deep convection to the southeast of Theta remains within about 60 n mi of the storm center, despite a hostile environment characterized by dry mid-level air and 40-50 kt of northerly shear. Unfortunately, several scatterometer passes this evening missed the core of the cyclone. Since the satellite presentation is generally unchanged from earlier today, the initial intensity is held at 35 kt, which is consistent with a T2.5 Dvorak classification received from TAFB.

Strong northerly shear and continued dry air entrainment will eventually take a toll on Theta, but recent satellite trends and the latest GFS simulated satellite imagery suggest that the cyclone could remain tropical a little longer than previously forecast. The latest NHC intensity forecast keeps Theta as a 35-kt tropical storm at 12 h before weakening it into a remnant low by 24 h. This follows the consensus of the latest intensity guidance. Thereafter, continued weakening is expected through its dissipation early next week.

Theta is still moving eastward at around 4 kt. The cyclone should begin turning northeastward later today, and then accelerate north-northeastward on Monday as the shallow remnant low is steered by a low-level ridge centered over northwestern Africa. The remains of Theta are forecast to open up into a trough and dissipate by 60 h ahead of an approaching cold front over the northeastern Atlantic. The latest NHC track forecast is adjusted slightly to the left of the previous one, which generally follows the latest track consensus aids. On the forecast track, the remnant low of Theta is expected to pass near the island of Madeira late Sunday night or early Monday.

FORECAST POSITIONS AND MAX WINDS

INIT  15/0300Z 31.7N  18.7W   35 KT  40 MPH - Tropical Storm (WSW Funchal, Madeira)
 12H  15/1200Z 31.9N  18.0W   35 KT  40 MPH - Tropical Storm (WSW Funchal, Madeira)
 24H  16/0000Z 32.6N  17.4W   30 KT  35 MPH - Low (WSW Funchal, Madeira)
 36H  16/1200Z 34.2N  17.1W   25 KT  30 MPH - Low (WNW Funchal, Madeira)
 48H  17/0000Z 36.7N  15.9W   20 KT  25 MPH - Low (WSW Lisbon, Portugal)
 60H  17/1200Z...DISSIPATED

NWS National Hurricane Center Miami FL 900 PM GMT Sat Nov 14, 2020 

A persistent band of deep convection to the southeast of Theta’s center continues to keep it classifiable as a tropical cyclone, with the edge of the convection at one point today reaching within 60 n mi of the center of the cyclone. Over the past couple of hours this convection has become farther displaced from Theta’s center, as the system gets blasted by over 40 kt of northerly shear. Since the cyclone’s appearance has changed little today, the initial intensity is being held at 35 kt based off data from an ASCAT-A overpass this morning. Very strong shear and dry air entrainment should cause the deep convection to weaken and become even farther displaced from the center tonight, with Theta anticipated to degenerate into a remnant low by 12 h. The cyclone should also weaken under this regime, and open into a trough by 72 h. The latest NHC intensity forecast is unchanged from the previous one, and is in good agreement with the intensity guidance.

Theta continues moving just south of due east, but now at a slower pace of around 5 kt. A mid-level ridge located to the south of Theta is weakening, which will result in a continued slow east-southeastward motion through tonight. As Theta becomes a shallow system on Sunday, the low-level flow is forecast to become southwesterly, and this flow is expected to increase on Monday ahead of an approaching cold front. This will cause Theta to turn to the northeast by late Sunday and accelerate until it dissipates in a few days. The latest NHC track forecast is similar to the previous one and lies near the track consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT  14/2100Z 31.7N  19.2W   35 KT  40 MPH - Tropical Storm (WSW Funchal, Madeira)
 12H  15/0600Z 31.7N  18.3W   30 KT  35 MPH - Low (WSW Funchal, Madeira)
 24H  15/1800Z 32.1N  17.5W   30 KT  35 MPH - Low (WSW Funchal, Madeira)
 36H  16/0600Z 33.2N  17.0W   25 KT  30 MPH - Low (WNW Funchal, Madeira)
 48H  16/1800Z 35.1N  16.4W   20 KT  25 MPH - Low (WNW Funchal, Madeira)
 60H  17/0600Z 38.1N  14.7W   20 KT  25 MPH - Low (WNW Funchal, Madeira)
 72H  17/1800Z...DISSIPATED

NWS National Hurricane Center Miami FL 300 PM GMT Sat Nov 14, 2020

Theta’s center continues to be devoid of deep convection as dry air entrains into the system’s circulation. The edge of the only nearby surviving convection is located about 60 n mi to the southeast of the cyclone’s center due to increasing northwesterly shear. A recent ASCAT overpass showed a fair amount of wind vectors of 30-34 kt, therefore the initial intensity remains 35 kt for this advisory. The shear is expected to increase even more today, and the surrounding environment is forecast to dry out further. These factors, that should persist for at least the next few days, should prevent any new convection from developing near the center of Theta. The latest NHC forecast calls for the system to become a remnant low in 12 h and dissipate in 72 h, as the circulation gradually spins down.

The storm is now moving just south of due east around 7 kt as it is steered along the northern periphery of a mid-level ridge. This ridge is forecast to weaken over the next couple of days, which will cause Theta to slow its forward motion. Early next week, increasing southerly flow ahead of an approaching cold front should pick up the remnants of Theta and accelerate them northward, and then northeastward. The latest NHC track forecast is similar to the previous one and lies near the track consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT  14/1500Z 31.8N  20.2W   35 KT  40 MPH - Tropical Storm (WSW Funchal, Madeira)
 12H  15/0000Z 31.6N  19.1W   35 KT  40 MPH - Low (WSW Funchal, Madeira)
 24H  15/1200Z 31.7N  18.3W   30 KT  35 MPH - Low (WSW Funchal, Madeira)
 36H  16/0000Z 32.4N  17.8W   25 KT  30 MPH - Low (WSW Funchal, Madeira)
 48H  16/1200Z 33.7N  17.4W   20 KT  25 MPH - Low (WNW Funchal, Madeira)
 60H  17/0000Z 36.1N  16.4W   20 KT  25 MPH - Low (WNW Funchal, Madeira)
 72H  17/1200Z...DISSIPATED

NWS National Hurricane Center Miami FL 300 AM GMT Sat Nov 14, 2020

Theta is beginning to show signs of weakening tonight. Infrared cloud top temperatures have warmed during the past several hours within the weakening convective band that curves around the northeastern semicircle of the storm. A partial 22 UTC ASCAT-B overpass indicates that Theta maintains a fairly symmetric low-level wind field, with 35-40 kt winds in the eastern semicircle of the storm. Therefore, the initial intensity is lowered to 45 kt with this advisory, which is consistent with UW-CIMSS objective current intensity estimates but slightly higher than the T2.5 subjective Dvorak classification from TAFB.

Theta will encounter increasingly hostile environmental conditions over the next couple of days. The NHC intensity forecast calls for steady weakening through the weekend, as strong northerly wind shear and cool sea surface temperatures will likely inhibit the storm from sustaining convection near its center. This forecast closely follows the corrected consensus aid HCCA. Theta is expected to weaken to a tropical depression within 36 h and degenerate into a remnant low by 48 h, although the GFS simulated satellite imagery suggests this could occur even sooner than forecast. The remnant low should dissipate by the middle of next week.

Theta is still moving eastward at around 9 kt around the northern periphery of a mid-level ridge that extends from western Africa across the eastern tropical Atlantic. An eastward or east-southeastward motion with a gradual decrease in forward speed is expected during the next 24-36 h. As the storm spins down and becomes a more shallow circulation, the remains of Theta will turn northward and then accelerate northeastward ahead of a mid-latitude cyclone and associated frontal system that will cross the northeastern Atlantic. The NHC track forecast lies close to the previous one and near the center of the guidance envelope. On the forecast track, the center of Theta is expected to pass northwest of the Canary Islands this weekend, then move near Madeira Island early Monday as a weak remnant low.

FORECAST POSITIONS AND MAX WINDS

INIT  14/0300Z 31.9N  21.6W   45 KT  50 MPH - Tropical Storm (WSW Funchal, Madeira)
 12H  14/1200Z 31.8N  20.2W   40 KT  45 MPH - Tropical Storm (WSW Funchal, Madeira)
 24H  15/0000Z 31.6N  18.6W   35 KT  40 MPH - Tropical Storm (WSW Funchal, Madeira)
 36H  15/1200Z 31.7N  17.8W   30 KT  35 MPH - Depression (WSW Funchal, Madeira)
 48H  16/0000Z 32.3N  17.5W   25 KT  30 MPH - Low (WSW Funchal, Madeira)
 60H  16/1200Z 33.7N  17.3W   25 KT  30 MPH - Low (WNW Funchal, Madeira)
 72H  17/0000Z 35.9N  16.0W   20 KT  25 MPH - Low (WNW Funchal, Madeira)
 96H  18/0000Z...DISSIPATED

NWS National Hurricane Center Miami FL 900 PM GMT Fri Nov 13, 2020 

Theta appears to be holding its own still, with a large curved band feature characterizing the bulk of the deep convection, and a smaller area of convection intermittently developing over the center. Like yesterday, there has been a lack of observational data over the system’s core since last night. However, since Theta’s organization has not appeared to change much since that time, the initial intensity is being kept at a somewhat uncertain 50 kt.

Theta is forecast to change little in intensity into tonight as the cyclone continues moving in a relatively low shear zone associated with a mid- to upper-level trough axis. By tomorrow, strong northerly shear is forecast to begin impacting the system while stable air gets entrained into its circulation. As a result, Theta is expected to spin down over the weekend, degenerate to a remnant low on Sunday, and dissipate by the middle of next week.

Theta is moving eastward at around 9 kt, steered by a mid-level ridge extending westward from west Africa to the eastern tropical Atlantic. A turn to the east-southeast along with a gradual slowing of the forward motion is expected overnight and continuing through the weekend as the ridge weakens, and mid- to upper level northerly winds impart on the cyclone. Early next week, what remains of Theta are expected to turn northward and then accelerate northeastward as a mid-latitude cyclone passes to the north of the region. The NHC forecast is little changed from the previous one and lies near the various consensus aids. On the forecast track, the center of Theta is forecast to track very near the westernmost Canary Islands. However, the system is forecast to weaken to a remnant low before reaching those islands.

FORECAST POSITIONS AND MAX WINDS

INIT  13/2100Z 31.9N  22.6W   50 KT  60 MPH - Tropical Storm (WSW Funchal, Madeira)
 12H  14/0600Z 31.7N  21.0W   50 KT  60 MPH - Tropical Storm (WSW Funchal, Madeira)
 24H  14/1800Z 31.4N  19.2W   45 KT  50 MPH - Tropical Storm (WSW Funchal, Madeira)
 36H  15/0600Z 31.3N  18.2W   40 KT  45 MPH - Tropical Storm (WSW Funchal, Madeira)
 48H  15/1800Z 31.7N  17.7W   30 KT  35 MPH - Low (WSW Funchal, Madeira)
 60H  16/0600Z 32.5N  17.7W   30 KT  35 MPH - Low (WSW Funchal, Madeira)
 72H  16/1800Z 34.4N  17.3W   25 KT  30 MPH - Low (WNW Funchal, Madeira)
 96H  17/1800Z 39.2N  12.8W   25 KT  30 MPH - Low (WNW Lisbon, Portugal)
120H  18/1800Z...DISSIPATED

NWS National Hurricane Center Miami FL 300 PM GMT Fri Nov 13, 2020 

Satellite images and microwave data this morning are showing that Theta finally has a more classic appearance of a tropical storm. There is a warming of cloud tops over the center, with a curved band of convection wrapping around the eastern portion of the circulation. The scatterometer overpasses missed the core of the cyclone this morning. However, since the cloud pattern has not degraded since the previous advisory, the intensity is being held at 50 kt for this advisory.

Theta is forecast to change little in intensity today as the cyclone continues moving in a low shear zone associated with a mid- to upper-level trough axis. By tomorrow, strong northerly shear is forecast to begin impacting the system while stable air gets entrained into its circulation. As a result, Theta is expected to spin down over the weekend, degenerate to a remnant low on Sunday, and dissipate by the middle of next week.

Theta continues to move eastward at around 10 kt, steered by a mid-level ridge extending westward from west Africa to the eastern tropical Atlantic. A turn to the east-southeast along with a gradual slowing of the forward motion is expected later today and continuing through the weekend as the ridge weakens, and mid- to upper level northerly winds impart on the cyclone. Early next week, what remains of Theta are expected to turn northward and then accelerate northeastward as a mid-latitude cyclone passes to the north of the region. The NHC forecast is little changed from the previous one and lies near the various consensus aids.

FORECAST POSITIONS AND MAX WINDS

INIT  13/1500Z 31.7N  23.8W   50 KT  60 MPH - Tropical Storm (WSW Funchal, Madeira)
 12H  14/0000Z 31.5N  22.2W   50 KT  60 MPH - Tropical Storm (WSW Funchal, Madeira)
 24H  14/1200Z 31.3N  20.4W   45 KT  50 MPH - Tropical Storm (WSW Funchal, Madeira)
 36H  15/0000Z 31.0N  19.1W   45 KT  50 MPH - Tropical Storm (WSW Funchal, Madeira)
 48H  15/1200Z 31.1N  18.3W   35 KT  40 MPH - Tropical Storm (WSW Funchal, Madeira)
 60H  16/0000Z 31.3N  18.1W   30 KT  35 MPH - Low (WSW Funchal, Madeira)
 72H  16/1200Z 32.8N  18.0W   30 KT  35 MPH - Low (WNW Funchal, Madeira)
 96H  17/1200Z 37.4N  15.6W   25 KT  30 MPH - Low (WNW Funchal, Madeira)
120H  18/1200Z...DISSIPATED

NWS National Hurricane Center Miami FL 300 AM GMT Fri Nov 13, 2020

The structure of Theta has been waxing and waning today with moderate convection attempting to wrap around the center, though the coldest cloud tops have been decaying before wrapping fully around. Earlier, there was a 2222 UTC partial ASCAT-B pass that showed peak winds of 40-45 kt on the south side of Theta. However the highest winds from this instrument the previous two nights were in the southwest quadrant and it is estimated that higher winds may still exist in this quadrant of Theta. For this reason, the latest intensity estimate is only adjusted downward to 50 kt for this advisory.

Theta continues to track east at 090/12 kt as the system remains steered by flow along the north side of a mid-level ridge. This ridge is forecast to gradually weaken over the next 24-36 h and Theta is forecast to bend to the east-southeast as the cyclone becomes more influenced by mid-level northerly flow associated with an upstream ridge building to the northwest. After 36 h, Theta is expected to slow down significantly as it becomes a shallow cyclone in light low-level flow. Finally, low-level southerly flow ahead of a mid-latitude cyclone is forecast to steer Theta’s remnant low northeastward by the end of the forecast. The track guidance this cycle has shifted a bit southward for the first part of the forecast, and the official NHC track forecast has been adjusted slightly further south, close to the reliable ICVN consensus.

Thus far, Theta has been struggling to produce deep convection that has successfully wrapped around its center. While Vertical Wind Shear is forecast to decrease per ECMWF-SHIPS guidance over the next 12-24 h, it remains to be seen if the current degree of instability is enough for Theta to take advantage of the more conducive wind environment. Thereafter, Vertical Wind Shear increases sharply from the north, importing a much more stable environment over Theta. For now, the latest NHC intensity forecast maintains the current 50 kt intensity over the next 24 h with weakening forecasted thereafter, in general agreement with the latest intensity guidance.

FORECAST POSITIONS AND MAX WINDS

INIT  13/0300Z 31.7N  26.0W   50 KT  60 MPH - Tropical Storm (WSW Funchal, Madeira)
 12H  13/1200Z 31.7N  24.2W   50 KT  60 MPH - Tropical Storm (WSW Funchal, Madeira)
 24H  14/0000Z 31.4N  22.1W   50 KT  60 MPH - Tropical Storm (WSW Funchal, Madeira)
 36H  14/1200Z 31.0N  20.4W   45 KT  50 MPH - Tropical Storm (WSW Funchal, Madeira)
 48H  15/0000Z 30.8N  19.2W   40 KT  45 MPH - Tropical Storm (WSW Funchal, Madeira)
 60H  15/1200Z 30.8N  18.6W   30 KT  35 MPH - Depression (WSW Funchal, Madeira)
 72H  16/0000Z 31.2N  18.5W   30 KT  35 MPH - Low (WSW Funchal, Madeira)
 96H  17/0000Z 34.3N  18.2W   25 KT  30 MPH - Low (WNW Funchal, Madeira)
120H  18/0000Z...DISSIPATED

NWS National Hurricane Center Miami FL 900 PM GMT Thu Nov 12, 2020 

The appearance and structure of Theta has changed little today, with intermittent bursts of convection wrapping mostly around the center of circulation. There has been no new observational data since last night, and it is still assumed that the cyclone’s intensity remains a somewhat uncertain 55 kt due to the consistency of its appearance.

Theta’s motion over the past 12 h is 090/10 kt as the cyclone continues to be steered around the north side of a mid-level ridge. A slower east-southeastward motion is expected from 36-72 h as the mid-level ridge to the south weakens and mid- to upper-level northerly flow moves over Theta. After 72 h, Theta or its remnants are expected to turn northeastward or northward and accelerate in the low-level flow ahead of an approaching mid-latitude cyclone over the northeastern Atlantic. The latest track forecast has changed little from the previous one and remains near the multi-model consensus tracks.

The shear across Theta is expected to relax somewhat over the next day or so, while the cyclone moves over cooler waters. These counteracting effects should allow the cyclone to maintain its intensity during that time. By this weekend, strong northerly shear is expected to impact Theta, while stable air gets entrained into its circulation. This should cause the cyclone to weaken, with the system likely degenerating into a remnant low by Sunday. The latest NHC intensity forecast is essentially unchanged from the previous one and is close to the various consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT  12/2100Z 31.7N  27.4W   55 KT  65 MPH - Tropical Storm (WSW Funchal, Madeira)
 12H  13/0600Z 31.8N  25.7W   55 KT  65 MPH - Tropical Storm (WSW Funchal, Madeira)
 24H  13/1800Z 31.8N  23.4W   55 KT  65 MPH - Tropical Storm (WSW Funchal, Madeira)
 36H  14/0600Z 31.5N  21.5W   55 KT  65 MPH - Tropical Storm (WSW Funchal, Madeira)
 48H  14/1800Z 31.2N  20.2W   45 KT  50 MPH - Tropical Storm (WSW Funchal, Madeira)
 60H  15/0600Z 31.1N  19.4W   35 KT  40 MPH - Tropical Storm (WSW Funchal, Madeira)
 72H  15/1800Z 31.4N  19.1W   30 KT  35 MPH - Low (WSW Funchal, Madeira)
 96H  16/1800Z 34.0N  19.1W   30 KT  35 MPH - Low (WNW Funchal, Madeira)
120H  17/1800Z 38.4N  15.4W   30 KT  35 MPH - Low (WSW LIsbon, Portugal)

NWS National Hurricane Center Miami FL 300 AM GMT Thu Nov 12, 2020 

The cloud appearance of Theta briefly became a bit more symmetric earlier tonight, though the colder cloud tops that attempted to wrap around the low-level center have recently decayed, possibly due to entrainment of dry mid-latitude air. A 2243 UTC ASCAT-B pass and a subsequent ASCAT-C pass both found the max winds with Theta a little stronger than previously estimated with maximum values exceeding 50 kt. These data support an initial intensity of 55 kt, and this could even be a little conservative.

Over the last 6 h Theta appears to have made a slight jog left of the previous forecast track, perhaps related to the convection wrapping around the center, but the longer term motion is still east-northeast at about 10 kt. Over the next day, Theta is expected to continue to move east-northeastward as it rounds the north side of a mid-level ridge centered over the Cape Verde islands. Between 48 h to 72 h Theta’s track is forecast to bend east and then east-southeast as the mid-level ridge to the south weakens a bit, and mid to upper-level northerly flow from a weak mid-level ridge attempts to build in to the west. The latest track guidance shows a fair amount of spread in how quickly Theta makes this bend to the east-southeast, and this is a large source of uncertainty in the forecast. The NHC track forecast splits the difference between the faster ECMWF and slower HMON/HWRF guidance, and is not far from the TVCN consensus.

The intensity forecast of Theta has been adjusted upward for the first 48 h due to the higher initial intensity. GFS-SHIPS diagnostics indicate the vertical wind shear will gradually decrease while Theta moves through an unstable temperature profile conducive for moderate to deep convection. Thereafter, the aforementioned upper-level northerly flow will lead to an increase in the vertical wind shear and import very stable mid-latitude air over Thetas circulation. Most of the reliable global model guidance shows Theta succumbing to these negative effects and becoming a remnant low by 96 h. The official intensity forecast shows the same, and is on the high side of the guidance but not far from any of the models since the spread is quite low.

FORECAST POSITIONS AND MAX WINDS

INIT  12/0300Z 31.1N  31.4W   55 KT  65 MPH - Tropical Storm (WSW Funchal, Madeira)
 12H  12/1200Z 31.5N  29.8W   55 KT  65 MPH - Tropical Storm (WSW Funchal, Madeira)
 24H  13/0000Z 32.0N  27.8W   55 KT  65 MPH - Tropical Storm (WSW Funchal, Madeira)
 36H  13/1200Z 32.1N  25.4W   55 KT  65 MPH - Tropical Storm (WSW Funchal, Madeira)
 48H  14/0000Z 31.8N  23.4W   50 KT  60 MPH - Tropical Storm (WSW Funchal, Madeira)
 60H  14/1200Z 31.4N  21.9W   45 KT  50 MPH - Tropical Storm (WSW Funchal, Madeira)
 72H  15/0000Z 31.2N  20.5W   40 KT  45 MPH - Tropical Storm (WSW Funchal, Madeira)
 96H  16/0000Z 31.2N  19.8W   30 KT  35 MPH - Low (WSW Funchal, Madeira)
120H  17/0000Z 35.6N  18.9W   30 KT  35 MPH - Low (WSW Funchal, Madeira)

NWS National Hurricane Center Miami FL 900 PM GMT Wed Nov 11, 2020

The deep convection associated with Theta has been trying to wrap around the cyclone’s low-level center today, and the system consists of a large curved band feature with clouds tops as cold as -65 degrees C. There was no complete sampling of the cyclone’s circulation by the scatterometers today. However, a partial ASCAT-C overpass this morning showed that 40-45 kt winds were occurring in the eastern semicircle. This portion of the circulation has previously been the weaker portion of Theta, which suggests some higher winds could be occurring in the western semicircle. Therefore, the initial intensity is being kept at a somewhat uncertain 50 kt.

Theta appears to be holding its own in an environment of strong southwesterly shear and over relatively cool water temperatures of about 24 degrees C, within a favorable unstable atmosphere. The cyclone will be traversing over progressively cooler waters over the next couple of days, and the shear is expected to only abate slightly. These somewhat counteracting factors should either allow Theta to maintain its intensity or slowly weaken during that time. Over the weekend, the upper-level winds are expected to increase and shift out of the north, and force more stable air across the cyclone. This should cause the convection to become displaced to the south of the center and gradually dissipate. The GFS/CMC/ECMWF simulated satellite imagery all indicate that the system should degenerate to a remnant low by 96 h. The latest NHC intensity forecast is similar to the previous one, and remains near the various multimodel consensus aids.

The storm is moving east-northeastward at around 11 kt, steered by mid-latitude westerlies to the north of a mid-level ridge. This steering pattern is expected to remain in place for the next couple of days. Model guidance is trending slower over the weekend, as they are indicating that the ridge will weaken at around the same time that the shear vector becomes northerly. This would cause the cyclone to slow its forward motion and turn to the right, which is now indicated in the official forecast. However, the latest NHC track remains a little north of the consensus track guidance during that time frame. By the end of the forecast period, an approaching mid-latitude trough and associated front should pick up what remains of Theta and begin to accelerate it to the northeast.

FORECAST POSITIONS AND MAX WINDS

INIT  11/2100Z 30.5N  31.9W   50 KT  60 MPH - Tropical Storm (WSW Funchal, Madeira)
 12H  12/0600Z 31.1N  30.2W   50 KT  60 MPH - Tropical Storm (WSW Funchal, Madeira)
 24H  12/1800Z 31.5N  27.8W   50 KT  60 MPH - Tropical Storm (WSW Funchal, Madeira)
 36H  13/0600Z 31.9N  25.4W   45 KT  50 MPH - Tropical Storm (WSW Funchal, Madeira)
 48H  13/1800Z 32.1N  23.5W   45 KT  50 MPH - Tropical Storm (WSW Funchal, Madeira)
 60H  14/0600Z 32.0N  22.3W   45 KT  50 MPH - Tropical Storm (WSW Funchal, Madeira)
 72H  14/1800Z 31.8N  21.3W   40 KT  45 MPH - Tropical Storm (WSW Funchal, Madeira)
 96H  15/1800Z 31.7N  19.7W   30 KT  35 MPH - Low (WSW Funchal, Madeira)
120H  16/1800Z 35.1N  18.2W   30 KT  35 MPH - Low (WSW Funchal, Madeira)

NWS National Hurricane Center Miami FL 300 PM GMT Wed Nov 11, 2020

Theta’s center continues to be devoid of deep convection, with the convective mass located primarily to the north of the center due to strong shear. A recent partial ASCAT overpass showed a slight decrease in the winds over the eastern semicircle. However, the pass did not sample the western portion of the circulation which has previously had the strongest winds. Based on the slightly lower ASCAT values, and the assumption that the rest of the vortex has spun down slightly due to the lack of convection over the center, the initial intensity is decreased to 50 kt.

Theta is moving east-northeastward at 9 kt, steered by the southern part of the mid-latitude westerlies to the north of a mid-level ridge. This steering pattern is expected to remain in place through much of the weekend. By early next week, the ridge is forecast weaken ahead of an approaching mid-latitude trough. This would cause the cyclone to slow its forward motion temporarily before it gets picked up by the trough. The latest NHC forecast is near the previous one through 72 h, and is a little slower during days 4-5 due to the slowing of the guidance. This latest forecast is very near the clustered track consensus models.

Despite the strong shear and cool water temperatures, the instability aloft should continue to support deep convection for at least the next few days. The shear is forecast to lessen somewhat in a day or so, but will still be relatively strong. Since the cyclone has been weakening slowly in the current environment, it is anticipated that the pace of weakening may lessen during the next few days with the decrease in shear. Beyond that time, the upper-level winds are forecast to become more northerly, and at about the same time the instability is forecast to decrease. These factors should cause any remaining convection to dissipate, with Theta likely becoming post-tropical by day 5. The latest NHC intensity forecast was adjusted slightly downward from the previous one mainly due to the lower initial intensity and is near the IVCN and HCCA consensus model forecasts.

FORECAST POSITIONS AND MAX WINDS

INIT  11/1500Z 29.8N  33.3W   50 KT  60 MPH - Tropical Storm (WSW Los Llanos, SCdT)
 12H  12/0000Z 30.3N  31.9W   50 KT  60 MPH - Tropical Storm (WSW Los Llanos, SCdT)
 24H  12/1200Z 30.7N  29.7W   45 KT  50 MPH - Tropical Storm (WSW Los Llanos, SCdT)
 36H  13/0000Z 31.1N  27.3W   45 KT  50 MPH - Tropical Storm (WSW Los Llanos, SCdT)
 48H  13/1200Z 31.5N  25.1W   45 KT  50 MPH - Tropical Storm (WNW Funchal, Madeira)
 60H  14/0000Z 31.8N  23.2W   45 KT  50 MPH - Tropical Storm (WNW Funchal, Madeira)
 72H  14/1200Z 31.9N  22.0W   40 KT  45 MPH - Tropical Storm (WNW Funchal, Madeira)
 96H  15/1200Z 32.2N  20.6W   35 KT  40 MPH - Tropical Storm (WNW Funchal, Madeira)
120H  16/1200Z 34.7N  19.2W   35 KT  40 MPH - Post Tropical ()

NWS National Hurricane Center Miami FL 300 AM GMT Wed Nov 11, 2020

Convection with Theta has waned some since the previous advisory, with the coldest cloud tops now focused in a band on the northeastern side of the partially exposed circulation. Despite this decrease in convective coverage, a 2304 UTC ASCAT-B pass showed a large region of 50 kt winds with at least one 55 kt barb. Accounting for a bit of undersampling of this instrument and maintaining continuity with the previous advisory, the maximum sustained winds have been kept at 60 kt for this advisory.

Theta has slowed a bit tonight on the same east-northeast heading at 075/10 kt. The steering philosophy in the first part of the forecast has remained the same, with Theta moving off to the east-northeast while it continues to round the northern edge of a mid-level ridge providing the steering flow. The latest track guidance has slowed down the forward motion a bit more this cycle, and the new track forecast splits the difference between the previous forecast and some of the more reliable global model guidance that is slower and south of the NHC track. At the end of the forecast period both the ECMWF and GFS are forecasting Theta to become a shallow vortex as the remaining convection is stripped away, and this could cause Theta to slow down in the weaker low-level flow and move more slowly to the northeast at the end of the forecast period.

Despite moving over gradually decreasing sea surface temperatures over the next 48-72 h, upper-level temperatures are also forecast to cool per GFS-SHIPS, which should provide enough instability for moderate to deep convection. In addition, vertical wind shear may decrease some in the 48-72 h period as Theta remains in light flow along an upper-level trough axis. Therefore, the latest NHC intensity forecast remains on the high end of the guidance for the first three days, but now shows a faster weakening trend thereafter as vertical wind shear increases out of the north and strips the remaining convection away. At 5 days the forecast now makes Theta a remnant low since it appears the circulation will be too shallow to take advantage of more favorable baroclinic conditions that would ordinarily allow for extratropical transition.

FORECAST POSITIONS AND MAX WINDS

INIT  11/0300Z 29.4N  35.5W   60 KT  70 MPH - Tropical Storm (WSW Los Llanos, SCdT)
 12H  11/1200Z 29.7N  34.2W   60 KT  70 MPH - Tropical Storm (WSW Los Llanos, SCdT)
 24H  12/0000Z 30.1N  32.5W   55 KT  65 MPH - Tropical Storm (WSW Los Llanos, SCdT)
 36H  12/1200Z 30.5N  30.4W   55 KT  65 MPH - Tropical Storm (WSW Los Llanos, SCdT)
 48H  13/0000Z 31.0N  27.7W   55 KT  65 MPH - Tropical Storm (WNW Funchal, Madeira)
 60H  13/1200Z 31.7N  25.2W   55 KT  65 MPH - Tropical Storm (WNW Funchal, Madeira)
 72H  14/0000Z 32.2N  23.2W   55 KT  65 MPH - Tropical Storm (WNW Funchal, Madeira)
 96H  15/0000Z 32.8N  21.4W   50 KT  60 MPH - Tropical Storm (WNW Funchal, Madeira)
120H  16/0000Z 34.5N  20.1W   40 KT  45 MPH - Low (WNW Funchal, Madeira)

NWS National Hurricane Center Miami FL 900 PM GMT Tue Nov 10, 2020 

A central dense overcast has persisted near the center of Theta since yesterday, and although the clouds tops have warmed over the past several hours there remains a distinct curved band feature over the northern portion of the circulation. Water vapor imagery shows the mid- upper-level trough that was over the Azores is beginning to leave the cyclone behind. Based on these factors, and the earlier indications of a compact radius of maximum winds, it appears that Theta has completed a transition to a tropical cyclone. Even though the clouds tops have recently warmed, the overall structure of Theta has not degraded by much since the previous advisory. Therefore, the initial intensity is being held at 60 kt.

The storm is moving 075/12 kt around the north side of a mid-level ridge. This feature should continue to steer Theta in a generally east-northeastward motion for the next few days. Late in the forecast period, the ridge will begin to weaken as another trough approaches from the northwest. This should cause the cyclone to slow its forward motion and begin to turn to the northeast. The latest model guidance has once again slowed down and the new NHC track forecast now lies between the previous one and the various consensus models.

Although Theta will be moving over progressively cooler SSTs and within moderate wind shear conditions, the air mass is expected to remain unstable for the next day or so, which should be supportive of deep convection. Therefore, little change is strength is indicated during that time. Some weakening is anticipated later in the forecast period as the airmass becomes more stable. By the end of the 5-day forecast period, the combination of the cooler waters and an approaching trough should result in extratropical transition. The NHC intensity forecast has changed little from the previous one and remains near the IVCN and HCCA consensus models. FORECAST POSITIONS AND MAX WINDS.

FORECAST POSITIONS AND MAX WINDS

INIT  10/2100Z 29.4N  36.2W   60 KT  70 MPH - Tropical Storm (WSW Los Llanos, SCdT)
 12H  11/0600Z 29.8N  34.7W   60 KT  70 MPH - Tropical Storm (WSW Los Llanos, SCdT)
 24H  11/1800Z 30.3N  32.8W   55 KT  65 MPH - Tropical Storm (WSW Los Llanos, SCdT)
 36H  12/0600Z 30.8N  30.5W   55 KT  65 MPH - Tropical Storm (WSW Los Llanos, SCdT)
 48H  12/1800Z 31.5N  28.0W   50 KT  60 MPH - Tropical Storm (WNW Funchal, Madeira)
 60H  13/0600Z 32.1N  25.7W   50 KT  60 MPH - Tropical Storm (WNW Funchal, Madeira)
 72H  13/1800Z 32.6N  23.8W   45 KT  50 MPH - Tropical Storm (WNW Funchal, Madeira)
 96H  14/1800Z 33.2N  20.5W   40 KT  45 MPH - Tropical Storm (WNW Funchal, Madeira)
120H  15/1800Z 34.4N  19.0W   35 KT  40 MPH - Post Tropical (WNW Funchal, Madeira)

NWS National Hurricane Center Miami FL 300 PM GMT Tue Nov 10, 2020 

Theta continues to exhibit a mix of tropical and subtropical characteristics. The cyclone has a fairly compact radius of maximum winds with a central dense overcast over the northern portion of the circulation. However, there is a strong subtropical jet located just to the south of Theta, and strong upper-level winds in the surrounding environment in the presence of an upper trough. Based on this inconclusive data, Theta is being maintained as a subtropical storm for this advisory. An ASCAT-B overpass this morning revealed 50-kt winds in the northwest and southwest quadrants, with several 55-60 kt wind vectors, some of those vectors outside of the deep convection making them more believable. Based on this, the initial advisory intensity has been set to 60 kt. The storm is moving just north of due east, or 085/13 kt.

Theta should continue to be steered eastward to east-northeastward during the next several days on the north side of a mid-level ridge. This motion should take the cyclone across the subtropical eastern Atlantic throughout the forecast period. The latest model guidance is a little faster and slightly north of the previous forecast track, and so the latest NHC forecast has been adjusted slightly as well.

Theta is still expected to transition to a tropical storm later today as it separates from the upper-level trough. Although Theta will be tracking over progressively cooler SSTs and within moderate wind shear conditions, the air mass is expected to remain unstable for the next couple of days, which should be supportive of deep convection. Therefore, little change is strength is indicated during that time. Some weakening is anticipated later in the forecast period as the airmass becomes more stable. The NHC intensity forecast is higher than the previous one primarily due to the higher initial intensity, and is near the IVCN and HCCA consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT  10/1500Z 29.0N  37.4W   60 KT  70 MPH - Tropical Storm (WSW Los Llanos, SCdT)
 12H  11/0000Z 29.1N  35.7W   60 KT  70 MPH - Tropical Storm (WSW Los Llanos, SCdT)
 24H  11/1200Z 29.7N  33.4W   60 KT  70 MPH - Tropical Storm (WSW Los Llanos, SCdT)
 36H  12/0000Z 30.4N  31.3W   55 KT  65 MPH - Tropical Storm (WSW Los Llanos, SCdT)
 48H  12/1200Z 31.1N  28.7W   55 KT  65 MPH - Tropical Storm (WNW Funchal, Madeira)
 60H  13/0000Z 31.7N  26.0W   50 KT  60 MPH - Tropical Storm (WNW Funchal, Madeira)
 72H  13/1200Z 32.2N  23.7W   45 KT  50 MPH - Tropical Storm (WNW Funchal, Madeira)
 96H  14/1200Z 33.0N  19.5W   40 KT  45 MPH - Tropical Storm (WNW Funchal, Madeira)
120H  15/1200Z 34.3N  17.0W   35 KT  40 MPH - Post Tropical (WNW Funchal, Madeira)

NWS National Hurricane Center Miami FL 300 AM GMT Tue Nov 10, 2020

Over the past 12 h convection has slowly consolidated near the center of a non-tropical area of low pressure over the far northeast Atlantic. Earlier, there was a 2325 UTC ASCAT-B pass that showed that the low-level circulation had become more detached from the warm frontal boundary located to its northeast. In addition, the ASCAT pass showed that winds have increased to near 45 kt on the southeast portion of the circulation near where coldest convective cloud tops were located. Both a 2137 UTC SSMIS and 2324 UTC AMSU microwave pass showed convective banding under the cirrus canopy near where the highest winds were observed. However, water vapor satellite imagery still shows the presence of a broad upper-level low tangled up with the low-level circulation embedded in the convection. Therefore, Theta has been designated as a subtropical storm with maximum wind of 45 kt.

Theta has been on a near due east heading over the last 12 h at 90/13 kt. Currently the cyclone is located south of a broad deep-layer longwave trough. This trough is expected to bypass the cyclone to the east and Theta will primarily be steered by southwesterly flow on the northern periphery of a mid-level ridge centered over the Cape Verde islands. This flow will steer Theta slowly to the east-northeast over the next 3-5 days. The track guidance is in good agreement with this solution, with only minor differences in across-track spread. There are somewhat larger differences in the along-track spread related to different forward motion, but the latest NHC track forecast elected to stay close to the track consensus at this time.

Thetas structure has evolved from a frontal cyclone to a subtropical cyclone, though a frontal boundary remains nearby on the northeast side of the circulation. This boundary is expected to gradually dissipate and Theta is expected to fully transition to a tropical storm in 24 h as convection erodes the upper-level cyclonic flow overhead. The maximum sustained winds were increased slightly in the first 12 h of the forecast but are kept at 50 kt through 120 h which is on the high end of the intensity guidance.

Theta is the 29th named storm in the record-breaking 2020 Atlantic Hurricane Season, breaking the previous record of 28th named storms in 2005.

FORECAST POSITIONS AND MAX WINDS

INIT  10/0300Z 28.8N  40.3W   45 KT  50 MPH - SubTropical Storm (WSW Los Llanos, SCdT)
 12H  10/1200Z 29.0N  38.6W   50 KT  60 MPH - SubTropical Storm (WSW Los Llanos, SCdT)
 24H  11/0000Z 29.1N  36.3W   50 KT  60 MPH - Tropical Storm (WSW Los Llanos, SCdT)
 36H  11/1200Z 29.5N  34.3W   50 KT  60 MPH - Tropical Storm (WSW Los Llanos, SCdT)
 48H  12/0000Z 30.0N  32.6W   50 KT  60 MPH - Tropical Storm (WSW Los Llanos, SCdT)
 60H  12/1200Z 30.5N  30.7W   50 KT  60 MPH - Tropical Storm (WSW Funchal, Madeira)
 72H  13/0000Z 31.0N  28.7W   50 KT  60 MPH - Tropical Storm (WSW Funchal, Madeira)
 96H  14/0000Z 32.2N  24.3W   50 KT  60 MPH - Tropical Storm (WSW Funchal, Madeira)
120H  15/0000Z 33.3N  20.6W   50 KT  60 MPH - Tropical Storm (WNW Funchal, Madeira)

NWS National Hurricane Center Miami FL 700 PM EST Mon Nov 9, 2020

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

The National Hurricane Center is issuing advisories on Tropical Storm Eta, located over the southeastern Gulf of Mexico.

  • 1. Shower and thunderstorm activity associated with a gale-force low pressure system located several hundred miles southwest of the Azores has become a little more concentrated near the center and it appears to be becoming more distinct from the frontal boundary located to the northeast of the system. If these trends continue, a subtropical or tropical storm is likely to form tonight or Tuesday while the system moves east or east-northeast over the northeastern Atlantic Ocean. * Formation chance through 48 hours…high…80 percent. * Formation chance through 5 days…high...90 percent.
  • 2. A tropical wave is forecast to move over the central Caribbean Sea, where an area of low pressure could form in a couple of days. Environmental conditions are forecast to be conducive for development, and a tropical depression could form late this week or over the weekend while the system moves slowly westward. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…medium…50 percent.

NWS National Hurricane Center Miami FL 700 AM EST Mon Nov 9, 2020

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

The National Hurricane Center is issuing advisories on Tropical Storm Eta, located off the southwest coast of Florida.

  • 1. Showers and thunderstorms associated with a non-tropical low-pressure system located several hundred miles southwest of the Azores continue to get gradually better organized. Further development is expected, and a tropical or subtropical storm will likely form during the next few days while the system moves eastward or east-northeastward over the northeastern Atlantic Ocean. * Formation chance through 48 hours…medium…50 percent. * Formation chance through 5 days…high…70 percent.
  • 2. A tropical wave is forecast to move over the central Caribbean Sea, where an area of low pressure could form in a couple of days. Environmental conditions are forecast to be conducive for development, and a tropical depression could form late this week or over the weekend while the system moves slowly westward. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…medium...50 percent.

NWS National Hurricane Center Miami FL 700 PM EST Sun Nov 8 2020

Corrected 5-day formation chance category for first disturbance

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

The National Hurricane Center is issuing advisories on Tropical Storm Eta, located just southeast of the southern Florida Peninsula and the Florida Keys.

  • 1. A low-pressure system is located several hundred miles southwest of the Azores. Shower and thunderstorm activity associated with the system is beginning to show some signs of organization. This low could develop further over the next several days, and a tropical or subtropical storm could develop by the end of the week while this system moves eastward or east-northeastward over the northeastern Atlantic Ocean. * Formation chance through 48 hours…low…30 percent. * Formation chance through 5 days…medium…40 percent.
  • 2. A tropical wave is forecast to move over the central Caribbean Sea, where an area of low pressure could form in a few days. Environmental conditions are forecast to be conducive for development as the system moves slowly westward through the end of the week. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low…30 percent.

NWS National Hurricane Center Miami FL 100 PM EST Sun Nov 8, 2020

For the North Atlantic…Caribbean Sea and the Gulf of Mexico: The National Hurricane Center is issuing advisories on Tropical Storm Eta, located just north of central Cuba.

  • 1. Recent satellite-derived wind data confirm that a low-pressure system has developed several hundred miles southwest of the Azores. Shower and thunderstorm activity associated with this system is currently disorganized. However, the low could slowly develop tropical or subtropical characteristics during the next several days while it moves eastward or east-northeastward over the northeastern Atlantic Ocean. * Formation chance through 48 hours…low…10 percent. * Formation chance through 5 days…low…30 percent.
  • 2. A tropical wave is forecast to move over the central Caribbean Sea, where an area of low pressure could form in a few days. Environmental conditions may be conducive for at least gradual development thereafter while the system moves slowly westward through the end of the week. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low…20 percent.

NWS National Hurricane Center Miami FL 700 AM EST Sun Nov 8, 2020

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

The National Hurricane Center is issuing advisories on Tropical Storm Eta, located over east-central Cuba.

  • 1. A broad non-tropical area of low pressure appears to be developing several hundred miles southwest of the Azores. This system could slowly develop subtropical characteristics later this week while it moves eastward or east-northeastward over the northeastern Atlantic Ocean. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low…20 percent.

NWS National Hurricane Center Miami FL 700 PM EST Sat Nov 7, 2020

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

The National Hurricane Center is issuing advisories on Tropical Storm Eta, located about 100 miles southwest of the coast of central Cuba.

  • 1. A broad non-tropical low pressure system could form several hundred miles south or southwest of the Azores early next week. Any subtropical development of this system is expected to be slow to occur while it moves generally eastward over the northeastern Atlantic Ocean through the middle of the week. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low...20 percent.

NWS National Hurricane Center Miami FL 100 PM EST Sat Nov 7, 2020

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

The National Hurricane Center is issuing advisories on Tropical Storm Eta, located just north of Grand Cayman Island.

  • 1. A broad non-tropical low pressure system could form several hundred miles southwest of the Azores early next week. Any subtropical development of this systems is expected to be slow to occur while it moves generally eastward over the northeastern Atlantic Ocean through the middle of the week. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low…20 percent.

NWS National Hurricane Center Miami FL 700 PM EST Fri Nov 6, 2020

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

  • The National Hurricane Center is issuing advisories on Tropical Depression Eta, located over the northwestern Caribbean Sea. 1. A broad non-tropical low-pressure system could form several hundred miles southwest of the Azores early next week. The system could gradually obtain some subtropical characteristics thereafter as it moves slowly northeastward over the northeastern Atlantic Ocean. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low…20 percent.

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

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Video: 2020 Hurricane season 8 (News Coverage of Hurricane Epsilon, Zeta, Eta & TS Theta)