Tropical Storm Gamma

Post Tropical Gamma Track 2200 Hours October 5 2020
Post Tropical Gamma Track 2200 Hours October 5 2020

Tropical Storm Gamma Wind Speed FieldTropical Storm GammaNWS National Hurricane Center Miami FL 1000 PM CDT Mon Oct 05, 2020 (see Mon 10:00 pm video below)

Gamma was entirely devoid of convection for most of the day. Shortly before sunset, a few disorganized thunderstorms developed to the southeast of the cyclone’s center, however these appear to be forced at least in part by a sea breeze boundary and are not exclusively associated with Gamma. A few other small cells of convection have developed to the west of Gamma’s center during the past hour or so, but not nearly enough to be considered sufficiently organized to meet the requirement for a tropical cyclone. Gamma is therefore now considered to be post-tropical and this will be the last NHC advisory.

The cyclone could still produce some additional disorganized convection and periods of heavy rain overnight as it moves inland over the Yucatan peninsula, but this is not expected to result in significant regeneration. Some of this rain could impact areas that are preparing for the much more significant approach of Hurricane Delta in a day or so. The cyclone is moving southwestward near 5 kt, and this should continue for another day or so until it dissipates. The winds associated with Gamma’s remnants should gradually weaken through that time, though the system could still produce a few areas of heavy rain over southeastern Mexico.

It is worth noting that several model trackers, and consequently the consensus aids, depict that Gamma will move northward over the Gulf of Mexico and strengthen significantly in a couple of days. This is because the trackers lose track of Gamma when it dissipates and start following nearby Hurricane Delta instead. In reality, no models forecast that Gamma will remain a well-defined cyclone for more than another day or two.

FORECAST POSITIONS AND MAX WINDS

INIT  06/0300Z 21.6N  88.4W   30 KT  35 MPH - Post Tropical (WNW  Rio Lagartos, Mexico)
 12H  06/1200Z 21.1N  88.9W   30 KT  35 MPH - Post Tropical (WSW Temax, Mexico)
 24H  07/0000Z 20.2N  89.6W   25 KT  30 MPH - Post Tropical (WSW Tabi, Mexico)
 36H  07/1200Z...DISSIPATED

NWS National Hurricane Center Miami FL 400 PM CDT Mon Oct 05, 2020  

The last couple of legs of the Air Force Reserve reconnaissance aircraft mission and recent METOP-A and C scatterometer passes support lowering Gamma’s initial intensity to 30 kt for this advisory. Conventional satellite imagery reveals that the cyclone has been devoid of deep convection for nearly 10 hours and is on its way to becoming a post-tropical remnant low. Strong southerly shear and a stable, relatively dry surrounding air mass should prevent any significant convective regeneration as the system approaches the northern coast of the northwestern Yucatan peninsula tomorrow. After the remnants of Gamma makes landfall, dissipation is likely to occur Wednesday as larger, Tropical Storm Delta approaches the Yucatan Channel.

The initial motion is estimated to be southwestward, or 230/4 kt. A continued southwestward or west-southwestward motion is expected through Wednesday morning while moving inland over the northern Mexican State of Yucatan. The NHC forecast track is basically an update of this morning’s package and is based on the various multi-model consensus aids.

KEY MESSAGES:

  • 1. Gamma is expected to produce areas of heavy rainfall through midweek over portions of southeast Mexico, including the Mexican states of Yucatan, Campeche, and Tabasco. This rainfall could result in areas of flash flooding.
  • 2. Gusty winds are likely along portions of the northern coast of the Yucatan Peninsula later today through Tuesday.
FORECAST POSITIONS AND MAX WINDS

INIT  05/2100Z 22.1N  88.1W   30 KT  35 MPH - Depression (ENE Rio Lagartos, Mexico)
 12H  06/0600Z 21.6N  88.8W   30 KT  35 MPH - Low (ENE Santa Clara, Mexico)
 24H  06/1800Z 20.9N  89.6W   25 KT  30 MPH - Low (WSW Leona Vicario, Mexico)
 36H  07/0600Z 20.0N  90.1W   20 KT  25 MPH - Low (ENE  Kankí, Mexico)
 48H  07/1800Z...DISSIPATED

NWS National Hurricane Center Miami FL 1000 AM CDT Mon Oct 05, 2020 

Air Force Reserve reconnaissance aircraft investigating Gamma found maximum 850 mb flight-level winds of 37 kt and surface SFMR peak winds of 40 kt, and the central pressure has increased to 1003 mb. Therefore, the initial intensity is lowered to 40 kt for this advisory. Stiff, persistent southerly shear, and an inhibiting thermodynamic surrounding environment should prevent Gamma from restrengthening, although, the Decay SHIPS intensity model does indicate a very brief period of decreasing shear magnitude just prior to landfall around the 24 hour period. Afterward, the shear, once again, increases. Gamma is expected to make landfall over the northwestern Yucatan peninsula on Tuesday and further weakening to a remnant low is forecast Wednesday as the cyclone remains inland over the northern Mexican State of Yucatan. Dissipation is likely to occur Friday over the region, if not sooner.

The initial motion is estimated to be a south-southwestward drift, or 205/2 kt. A turn southwestward or west-southwestward is expected by tonight and this general motion should continue through Wednesday morning while moving inland over the northern Mexican State of Yucatan. The large-scale models still insist on some binary interaction occurring with Tropical Storm Delta commencing Tuesday night/Wednesday morning. This should cause Gamma to gradually turn cyclonically through Thursday while remaining over the Northern Yucatan peninsula. If there is a delay in Gamma’s landfall, or the cyclone does remain just offshore, similar to the outlier UKMET, then Tropical Storm Delta could end up absorbing the smaller Gamma tropical cyclone toward the end of the week. For now, the NHC forecast will side with a landfall scenario which agrees with the HCCA consensus and the GFS/ECMWF solutions.

KEY MESSAGES:

  • 1. Gamma is expected to produce heavy rainfall through midweek over portions of southeast Mexico, including the Mexican states of Yucatan, Campeche, and Tabasco. This rainfall could result in significant flash flooding.
  • 2. Even though Gamma is just offshore, tropical storm conditions are likely along portions of the northern coast of the Yucatan Peninsula later today.
FORECAST POSITIONS AND MAX WINDS

INIT  05/1500Z 22.3N  87.6W   40 KT  45 MPH - Tropical Storm (WNW Holbox, Mexico)
 12H  06/0000Z 22.1N  88.4W   40 KT  45 MPH - Tropical Storm (WNW Rio Lagartos, Mexico)
 24H  06/1200Z 21.6N  89.2W   35 KT  40 MPH - Tropical Storm (ENE Telchac Puerto, Mexico)
 36H  07/0000Z 20.9N  89.9W   30 KT  35 MPH - Tropical Storm (WNW Samahil, Mexico )
 48H  07/1200Z 20.2N  90.2W   25 KT  30 MPH - Post Tropical (WNW Pomuch, Mexico)
 60H  08/0000Z 20.3N  89.8W   25 KT  30 MPH - Post Tropical (WSW Uxmal, Mexico)
 72H  08/1200Z 21.0N  89.5W   20 KT  25 MPH - Post Tropical (ESE Sitpach, Mexico)
 96H  09/1200Z...DISSIPATED

NWS National Hurricane Center Miami FL 1000 PM CDT Sun Oct 04, 2020

Gamma has moved much farther northeast than previously anticipated. With little in the way of low or mid-level large-scale steering flow currently in place, it seems likely that upper-level southwesterlies, also responsible for the shear affecting the tropical storm, are causing this recent northeastward motion. This may be either through reformations of the center closer to the convection or a direct contribution to the net steering. An Air Force Reserve Hurricane Hunter aircraft is currently investigating Gamma and so far has found max SFMR winds of 47 kt but flight level winds of only 45 kt. Given the data so far, there is no indication that Gamma is any stronger than the 50 kt intensity, but it seems prudent to let the plane finish its pattern before lowering the winds at this time.

Gamma’s future track is highly uncertain. The track guidance spread is much higher than usual, and confidence in the forecast is accordingly low. Most of the global models indicate that Gamma will soon begin moving generally west-southwestward as a mid-level ridge briefly builds over the eastern and central Gulf of Mexico. Unfortunately, there is little agreement on exactly when this will happen or how fast Gamma will move once it turns. After about 48 h, Gamma could interact with Tropical Depression Twenty-Six, which is forecast to move over the northwestern Caribbean Sea at that time. Current dynamical models are notoriously bad at forecasting such interactions, but if the two systems do interact it will likely cause Gamma to move inland over the Yucatan.

Whether such an interaction occurs or not, continued shear and proximity to land should cause the tropical storm to gradually weaken, and Gamma could dissipate if it moves over land (and stays there) in a few days, as shown by the GFS. The ECMWF shows the vortex remaining over water but dissipating nonetheless, while a couple other global models maintain the vortex longer and show it moving north over the central Gulf of Mexico late in the forecast period. The NHC forecast is a compromise between those solutions, showing a remnant low moving north over the southern Gulf of Mexico by day 5. In general, the NHC intensity forecast is similar to the previous one, but slightly lower to account for the system potentially moving inland.

Due to the uncertainty in the forecast at this time, future advisories may feature larger than normal changes to the track or intensity forecast. It is also worth noting that several dynamical model trackers appear to lose Gamma and jump to tracking Tropical Depression Twenty-Six when it reaches the Gulf of Mexico, resulting in unrealistic depictions of the intensity and track forecasts.

KEY MESSAGES:

  • 1. Gamma is expected to produce heavy rainfall for several days over portions of southeastern Mexico, the Yucatan Peninsula, Central America, and far western Cuba. This rainfall could result in life-threatening flash flooding and mudslides, particularly in the mountainous regions of southeastern Mexico and Central America.
  • 2. Even though Gamma is just offshore, tropical storm conditions are likely along portions of the northern coast of the Yucatan Peninsula on Monday.
FORECAST POSITIONS AND MAX WINDS

INIT  05/0300Z 22.8N  87.2W   50 KT  60 MPH - Tropical Storm (WNW Cancun, Mexico)
 12H  05/1200Z 22.7N  87.7W   45 KT  50 MPH - Tropical Storm (WNW El Cayo, Mexico)
 24H  06/0000Z 22.3N  88.5W   45 KT  50 MPH - Tropical Storm (WNW Rio Lagartos, Mexico)
 36H  06/1200Z 21.8N  89.5W   40 KT  45 MPH - Tropical Storm (WNW Telchac Puerto, Mexico)
 48H  07/0000Z 21.3N  90.3W   40 KT  45 MPH - Tropical Storm (WNW Piedra, Mexico)
 60H  07/1200Z 20.3N  90.7W   35 KT  40 MPH - Tropical Storm (WNW Nitun, Mexico)
 72H  08/0000Z 20.2N  90.1W   30 KT  35 MPH - Extra Tropical (WSW Pocboc, Mexico)
 96H  09/0000Z 22.0N  90.7W   30 KT  35 MPH - Extra Tropical (WNW Progreso, Mexico)
120H  10/0000Z 24.0N  91.0W   30 KT  35 MPH - Low (ENE Tampico, Mexico)

NWS National Hurricane Center Miami FL 400 PM CDT Sun Oct 04, 2020 

The last aircraft reconnaissance fix, recorded a couple of hours ago, indicated that Gamma’s center had wobbled a little to the right of the previous 6-hour motion and is located near the southeastern edge of the convective canopy. Flight-level winds adjusted to the surface, SFMR wind data, and a blend of Dvorak satellite intensity estimates from TAFB and SAB still support an initial intensity of 50 kt for this advisory.

The UW-CIMSS shear analysis reveals stiff 20-25 kt southerly shear impinging on the south portion of the cyclone. Subsequently, the large-scale models and the ECMWF/GFS statistical-dynamical intensity guidance show the shear magnitude increasing during the next 24 hours. This inhibiting upper wind pattern should induce weakening soon. Although the shear is predicted to decrease somewhat around mid-period, Gamma should exhibit little change in strength through the remaining period which is in best agreement with all of the skilled intensity guidance. As mentioned in previous advisories, it cannot be stressed enough the relatively high level of uncertainty in this intensity forecast, and that it’s primarily dependent on whether or not the cyclone moves back over the Yucatan Peninsula.

Gamma should continue to move little, or meander over the southern Gulf of Mexico, near the northern coast of the Yucatan Peninsula through most of tomorrow. By Monday night, the global models are in good agreement with the western extent of a subtropical ridge reestablishing temporarily over the central Gulf of Mexico. This change in the synoptic steering pattern should cause the cyclone to turn and move west-southwestward through the 72 hour forecast period. After a brief reduction in forward speed late Wednesday, while Potential-Tropical Cyclone Twenty-Six moves into the central Gulf of Mexico, a turn toward the northwest is expected on Thursday as the ridge, once again, builds back over the central Gulf in response to PTC Twenty-Six approaching the northern Gulf coast. The official track forecast is adjusted to the left of the previous one through the 60 hour period to agree more with the HCCA consensus, and shifted to the right through day 5.

KEY MESSAGES:

  • 1. Gamma is expected to produce heavy rainfall for several days over portions of southeastern Mexico, the Yucatan Peninsula, Central America, and far western Cuba. This rainfall could result in life-threatening flash flooding and mudslides, particularly in the mountainous regions of southeastern Mexico and Central America.
  • 2. Even though Gamma is just offshore, tropical storm conditions will continue across portions of the northern coast of the Yucatan Peninsula today.
FORECAST POSITIONS AND MAX WINDS

INIT  04/2100Z 22.4N  87.8W   50 KT  60 MPH - Tropical Storm (ENE Rio Lagartos, Mexico)
 12H  05/0600Z 22.3N  88.1W   45 KT  50 MPH - Tropical Storm (ENE Rio Lagartos, Mexico)
 24H  05/1800Z 22.1N  88.6W   40 KT  45 MPH - Trop ical Storm (WNW Rio Lagartos, Mexico)
 36H  06/0600Z 21.7N  89.4W   40 KT  45 MPH - Tropical Storm (WNW Telchac Puerto, Mexico)
 48H  06/1800Z 21.3N  90.4W   40 KT  45 MPH - Tropical Storm (WNW Piedra, Mexico)
 60H  07/0600Z 20.8N  91.1W   40 KT  45 MPH - Tropical Storm (WSW Celestún, Mexico)
 72H  07/1800Z 20.1N  91.4W   40 KT  45 MPH - Tropical Storm (WNW Campeche, Mexico)
 96H  08/1800Z 21.0N  92.1W   40 KT  45 MPH - Tropical Storm (WNW Celestún, Mexico)
120H  09/1800Z 22.2N  92.7W   40 KT  45 MPH - Tropical Storm (ESE Tampico, Mexico)

NWS National Hurricane Center Miami FL 1000 AM CDT Sun Oct 04, 2020 

An Air Force Reserve reconnaissance aircraft has found the center of Gamma over the far southern Gulf of Mexico, just north of the Yucatan Peninsula. Early morning visible satellite imagery has revealed decent banding structure over the northern and western portions of the circulation. The aircraft has measured a peak 850 mb flight-level wind of 66 kt and SFMR winds of 47 kt. A blend of these data support an initial intensity of 50 kt, which is also in line with the latest Dvorak classifications of T3.0 and T3.5 from SAB and TAFB, respectively.

Gamma appears to be slowing down as anticipated, with an initial motion estimate of 360/3 kt. Gamma is expected to meander over the southern Gulf of Mexico, just north of the northern coast of the Yucatan peninsula during the next 12-24 hours. By late Monday, the western portion of a subtropical ridge is expected to build westward over the northern Gulf of Mexico. This should cause Gamma to turn westward to west-southwestward through the remainder of the forecast period. The dynamical model guidance is in general agreement on this scenario, but there are some differences in how close Gamma tracks to the northwestern portion of the Yucatan peninsula. The NHC track splits these differences and is a blend TCVA multi-model consensus and the HFIP corrected consensus. The new track forecast is very close to the previous official forecast.

Although Gamma has re-strengthened this morning, increasing southerly wind shear is expected over the cyclone by tonight. This unfavorable upper-level environment is likely to cause some gradual weakening by late tonight and Monday. Since the vertical shear expected to remain moderate to strong through the latter portion of the forecast period, little overall change in strength is shown after 48 hours.

KEY MESSAGES:

  • 1. Gamma is expected to produce heavy rainfall for several days over portions of southeastern Mexico, the Yucatan Peninsula, Central America, and far western Cuba. This rainfall could result in life-threatening flash flooding and mudslides, particularly in the mountainous regions of southeastern Mexico and Central America.
  • 2. Even though Gamma is offshore, tropical storm conditions will continue across portions of the northern coast of the Yucatan Peninsula today.
FORECAST POSITIONS AND MAX WINDS

INIT  04/1500Z 22.2N  88.2W   50 KT  60 MPH - Tropical Storm (WNW Rio Lagartos, Mexico)
 12H  05/0000Z 22.6N  88.2W   50 KT  60 MPH - Tropical Storm (WNW Rio Lagartos, Mexico)
 24H  05/1200Z 22.6N  88.5W   45 KT  50 MPH - Tropical Storm (WNW Rio Lagartos, Mexico)
 36H  06/0000Z 22.3N  89.3W   40 KT  45 MPH - Tropical Storm (WNW Progreso, Mexico)
 48H  06/1200Z 22.0N  90.2W   40 KT  45 MPH - Tropical Storm (WNW Progreso, Mexico)
 60H  07/0000Z 21.5N  91.0W   40 KT  45 MPH - Tropical Storm (WNW Sisal, Mexico)
 72H  07/1200Z 21.0N  91.6W   40 KT  45 MPH - Tropical Storm (WSW Celestún, Mexico)
 96H  08/1200Z 20.4N  92.5W   40 KT  45 MPH - Tropical Storm (ENE Campeche, Mexico)
120H  09/1200Z 20.4N  93.0W   40 KT  45 MPH - Tropical Storm (WNW Campeche, Mexico)

NWS National Hurricane Center Miami FL 1000 PM CDT Sat Oct 03, 2020 

Tropical Storm Gamma remains over the northern portion of the Yucatan Peninsula, and the cyclone has been inland for about 10 hours now. Although the storm has weakened some, satellite images show that Gamma still has an intact central dense overcast feature and spiral bands on the north side of the circulation. The initial intensity is estimated to be 50 kt, but there is quite of bit of uncertainty in this value. The tropical storm is drenching the northern portion of the Yucatan Peninsula, and heavy rainfall is likely to continue there into Sunday.

The tropical storm is moving northwestward at 6 kt on the southwestern periphery of an Atlantic subtropical ridge. Gamma is expected to move very slowly to the northwest or north-northwest toward a weakness in the ridge during the next 12 to 24 hours, and that should take the core of the tropical storm over the extreme southern Gulf of Mexico by early Sunday. By Sunday night and Monday, a combination of a building low- to mid-level ridge over the Gulf of Mexico and a developing low pressure area over the northwestern Caribbean Sea should cause Gamma to turn fairly sharply to the west or southwest early next week. A slow southwest or west motion is likely to continue into the middle of next week, and some of the models suggest that Gamma could become nearly stationary by the end of the forecast period. The NHC track forecast is largely an update of the previous one and lies near the TVCA and HCCA consensus models.

The intensity forecast seems tricky. The tropical storm still appears well organized despite its time over land and since it will be moving back over water soon, it could re-strengthen. However, none of the intensity models show much strengthening, in fact, most of them show Gamma gradually weakening throughout the forecast period. On one hand, the storm is going to be over the warm Gulf of Mexico waters for several days, which favors strengthening. On the other hand, there is a fair amount of dry air over the western Gulf of Mexico and this could entrain into the circulation. Another complicated factor is how Gamma interacts with a developing low over the northwestern Caribbean Sea and a disturbance to its south. Based on these complexities, the NHC intensity forecast shows no change in strength through the forecast period, and lies near the high end of the guidance near the SHIPS model.

KEY MESSAGES:

  • 1. Gamma is expected to produce heavy rainfall for several days over portions of southeastern Mexico, the Yucatan Peninsula, Central America, and far western Cuba. This rainfall could result in life-threatening flash flooding and mudslides, particularly in the mountainous regions of southeastern Mexico and Central America.
  • 2. Even though Gamma is inland, tropical storm conditions will continue across portions of the Yucatan Peninsula tonight and Sunday.
FORECAST POSITIONS AND MAX WINDS

INIT  04/0300Z 21.3N  88.0W   50 KT  60 MPH - Tropical Storm (ENE Tizimín, Mexico)
 12H  04/1200Z 21.8N  88.2W   50 KT  60 MPH - Tropical Storm (WNW Rio Lagartos, Mexico)
 24H  05/0000Z 22.2N  88.5W   50 KT  60 MPH - Tropical Storm (WNW Rio Lagartos, Mexico)
 36H  05/1200Z 22.1N  88.9W   50 KT  60 MPH - Tropical Storm (WNW Progreso, Mexico)
 48H  06/0000Z 21.8N  89.9W   50 KT  60 MPH - Tropical Storm (WNW Progreso, Mexico)
 60H  06/1200Z 21.3N  90.9W   50 KT  60 MPH - Tropical Storm (WNW Sisal, Mexico)
 72H  07/0000Z 20.7N  91.7W   50 KT  60 MPH - Tropical Storm (WSW Celestún, Mexico)
 96H  08/0000Z 20.0N  92.5W   50 KT  60 MPH - Tropical Storm (WNW Campeche, Mexico)
120H  09/0000Z 19.9N  93.3W   50 KT  60 MPH - Tropical Storm (ENE Paraíso, Mexico)

NWS National Hurricane Center Miami FL 400 PM CDT Sat Oct 03, 2020 

Surface observations from the Yucatan Peninsula along with high-resolution visible satellite imagery indicated that the center of Gamma made landfall in the vicinity of Tulum, Mexico, shortly before 1700 UTC. Earlier aircraft observations and pressure measurements from Tulum showed that the system was very near hurricane strength when it made landfall. A ragged eye appeared in the visible images shortly after the center crossed the coast, but that feature has since become obscured. Since Gamma has likely been slowly weakening while moving over land, the current intensity has been set to 55 kt. Continued gradual weakening is likely into Sunday while the center either moves over land or interacts with nearby land. Some re-strengthening is expected to begin by Monday, but the numerical guidance is not very enthusiastic about intensification over the Gulf, probably due to the combination of drier air and the interaction with another low pressure system to the east. The official intensity forecast is not much different from the model consensus.

Gamma has been moving northwestward, but it is expected to turn north-northwestward while moving near and into a weakness in the subtropical ridge over the next day or so. The global models predict that a trough to the north of the tropical cyclone will lift northeastward and bypass Gamma. In a couple of days, a ridge is forecast to build back, albeit weakly, across the Gulf of Mexico. This is expected to cause the system to turn westward to southwestward over the latter part of the forecast period. The more reliable global models show the system meandering over the southern Bay of Campeche in 4 to 5 days, and so does the official forecast.

KEY MESSAGES:

  • 1. Gamma is expected to produce heavy rainfall for several days over portions of southeastern Mexico, the Yucatan Peninsula, Central America, and far western Cuba. This rainfall could result in life-threatening flash flooding and mudslides, particularly in the mountainous regions of southeastern Mexico and Central America.
  • 2. Even though Gamma has moved inland, tropical storm conditions will continue along the east coast of the Yucatan Peninsula through this evening and are expected to spread along the north coast within the Tropical Storm Warning area tonight and on Sunday.
FORECAST POSITIONS AND MAX WINDS

INIT  03/2100Z 20.7N  87.7W   55 KT  65 MPH - Tropical Storm (WSW X-Can, Mexico)
 12H  04/0600Z 21.3N  88.0W   45 KT  50 MPH - Tropical Storm (WSW Emal, Mexico)
 24H  04/1800Z 22.0N  88.2W   40 KT  45 MPH - Tropical Storm (WNW Rio Lagartos, Mexico)
 36H  05/0600Z 22.1N  88.4W   40 KT  45 MPH - Tropical Storm (WNW Rio Lagartos, Mexico)
 48H  05/1800Z 22.0N  89.1W   45 KT  50 MPH - Tropical Storm (ENE Telchac Puerto, Mexico)
 60H  06/0600Z 21.6N  90.4W   50 KT  60 MPH - Tropical Storm (WNW Progreso, Mexico)
 72H  06/1800Z 21.0N  91.5W   50 KT  60 MPH - Tropical Storm (WNW Celestún, Mexico)
 96H  07/1800Z 20.0N  92.0W   45 KT  50 MPH - Tropical Storm (WNW Campeche, Mexico)
120H  08/1800Z 20.0N  93.0W   40 KT  45 MPH - Tropical Storm (ENE Paraíso, Mexico)

NWS National Hurricane Center Miami FL 1000 AM CDT Sat Oct 03, 2020

Observations from both the Air Force and NOAA Hurricane Hunters indicate that Gamma has continued to strengthen this morning. The cloud pattern has continued to become better organized, with an eye trying to become evident on high-resolution satellite images from the GOES-16 mesoscale sectors. Flight-level and SFMR-observed surface winds from the aircraft support an intensity of 60 kt, and the storm could strengthen a little more as long as the center remains over water. Since Gamma will be near or at hurricane intensity when it makes landfall later today, the government of Mexico has issued a Hurricane Warning for a portion of the northeastern Yucatan Peninsula. Gamma should weaken some while it moves over land tonight. Some re-intensification is likely after the center moves into the southern Gulf of Mexico. However, the numerical guidance does not show much strengthening during the next few days, possibly due to the influence of drier air and/or the interaction with another area of low pressure to the east of Gamma. The official intensity forecast is near or above the model consensus.

Gamma continues northwestward at near 8 kt. The cyclone is expected to turn north-northwestward and move through a break in the subtropical ridge through 36 hours or so. Thereafter, a trough to the north moves eastward, bypassing Gamma, and later in the forecast period a ridge builds weakly over the Gulf of Mexico. This should cause the cyclone to turn toward the west and southwest. The official track forecast is close to the multi-model consensus, TVCN.

Although Gamma has strengthened, its biggest threat continues to be torrential rains, flooding, and mudslides especially near and over mountainous terrain.

KEY MESSAGES:

  • 1. Gamma is expected to produce heavy rainfall for several days over portions of southeastern Mexico, the Yucatan Peninsula, Central America, and far western Cuba. This rainfall could result in life-threatening flash flooding and mudslides, particularly in the mountainous regions of southeastern Mexico and Central America.
  • 2. Gamma is very near hurricane strength and will be near or at hurricane intensity when the center moves inland over the Yucatan Peninsula later today. A Hurricane Warning is now in effect for portions of the east coast of the Yucatan Peninsula, where tropical storm conditions are already occurring. Tropical storm conditions are expected along the north coast of the Yucatan Peninsula within the Tropical Storm Warning area later today and on Sunday.
FORECAST POSITIONS AND MAX WINDS

INIT  03/1500Z 20.0N  87.3W   60 KT  70 MPH - Tropical Storm (ESE Tulum, Mexico)
 12H  04/0000Z 20.8N  87.8W   55 KT  65 MPH - Tropical Storm (WNW Cocoyol, Mexico)
 24H  04/1200Z 21.8N  88.1W   40 KT  45 MPH - Tropical Storm (ENE Rio Lagartos, Mexico)
 36H  05/0000Z 22.2N  88.3W   40 KT  45 MPH - Tropical Storm (ENE Progreso, Mexico)
 48H  05/1200Z 22.3N  88.8W   45 KT  50 MPH - Tropical Storm (WNW Rio Lagartos, Mexico)
 60H  06/0000Z 22.1N  89.7W   50 KT  60 MPH - Tropical Storm (ENE Progreso, Mexico)
 72H  06/1200Z 22.0N  91.0W   50 KT  60 MPH - Tropical Storm (WNW Progreso, Mexico)
 96H  07/1200Z 21.0N  92.5W   45 KT  50 MPH - Tropical Storm (WNW Celestún, Mexico) 
120H  08/1200Z 20.0N  93.5W   40 KT  45 MPH - Tropical Storm (WNW Campeche, Mexico)

NWS National Hurricane Center Miami FL 1000 PM CDT Fri Oct 02, 2020 

A few hours ago, the Air Force Hurricane Hunters found maximum winds of around 35 kt in the northeastern quadrant of the cyclone, which was the reason why it was upgraded to Tropical Storm Gamma. Since then, there have been no stronger winds reported so the initial intensity remains 35 kt. The minimum pressure estimated by the aircraft is quite low at 998 mb, so it seems likely that the winds will increase soon.

The storm also has better banding features compared to hours ago and deep convection has also been persisting near the center. Fixes from the aircraft indicate that Gamma has jogged to the left recently, but smoothing through the short-term jog suggests an initial motion of 310/8 kt. The tropical storm is expected to remain on the western periphery of a subtropical high during the next couple of days, and that should cause the storm to move slowly northwestward during that time period. This track should take Gamma across the northern Yucatan Peninsula and perhaps over the extreme south-central Gulf of Mexico this weekend. By early next week, a mid-level ridge is expected to build to the north of the storm while another low pressure area is forecast to develop to the east of Gamma. This change in the steering pattern is expected to cause the storm to make a sharp left turn toward the Bay of Campeche, but continue to move at a fairly slow forward speed. The models have shifted well to the south from 48-120 hours this cycle, and the NHC track forecast has been adjusted in that direction. Despite the shift, most of the reliable models are south of the new official track forecast, and future southward adjustments could be necessary.

Environmental conditions appear generally favorable for additional strengthening until the cyclone reaches the Yucatan Peninsula on Saturday, and the NHC intensity forecast shows a slightly higher landfall intensity there. Once the system moves over the Yucatan Peninsula and the extreme southern Gulf of Mexico, the combination of land interaction, an increase in shear, and drier air should limit the amount of strengthening into next week. At this point, no model shows Gamma becoming a hurricane, and the NHC intensity forecast shows little change in strength for much of the forecast period.

The biggest threat from this large and slow-moving storm is the the potential for heavy rainfall and flooding, particularly near and over mountainous terrain.

KEY MESSAGES:

  • 1. Gamma is expected to produce heavy rainfall that could result in life-threatening flash flooding over portions of the Yucatan Peninsula, far western Cuba and well away from the center in the Mexican states of Campeche, Tabasco, and northern Chiapas.
  • 2. Gamma is forecast to bring tropical storm conditions to portions of the Yucatan Peninsula on Saturday, where a Tropical Storm Warning is in effect.
FORECAST POSITIONS AND MAX WINDS

INIT  03/0300Z 19.1N  86.1W   35 KT  40 MPH - Tropical Storm (ESE Punta Allen, Mexico)
 12H  03/1200Z 19.8N  86.9W   45 KT  50 MPH - Tropical Storm (ENE Mahahual, Mexico)
 24H  04/0000Z 20.8N  87.6W   45 KT  50 MPH - Tropical Storm (WNW Playa del Carmen, Mexico)
 36H  04/1200Z 21.6N  88.0W   40 KT  45 MPH - Tropical Storm (WNW Emal, Mexico)
 48H  05/0000Z 22.0N  88.3W   40 KT  45 MPH - Tropical Storm (WNW Rio Lagartos, Mexico)
 60H  05/1200Z 21.9N  88.9W   40 KT  45 MPH - Tropical Storm (WNW Progreso, Mexico)
 72H  06/0000Z 21.7N  90.0W   45 KT  50 MPH - Tropical Storm (WNW Progreso, Mexico)
 96H  07/0000Z 21.0N  91.8W   45 KT  50 MPH - Tropical Storm (WNW Campeche, Mexico)
120H  08/0000Z 20.3N  92.8W   45 KT  50 MPH - Tropical Storm (ENE Paraíso, Mexico)

NWS National Hurricane Center Miami FL 400 PM CDT Fri Oct 02, 2020

Convective banding features have become a little better defined over the southern portion of the circulation, but otherwise the system has not changed much in organization since earlier today. The current intensity estimate remains at 30 kt in agreement with a Dvorak estimate from TAFB, and scatterometer observations from a few hours ago. The SHIPS model output now shows some south-southwesterly shear affecting the system during the next few days. Otherwise, the environment should favor at least gradual strengthening, and the cyclone is likely to become a tropical storm prior to moving near the Yucatan Peninsula. The official intensity forecast is within the range of most of the model guidance.

The initial motion estimate is the same as in the morning advisory, 315/8 kt. The depression should move along the southwestern periphery of a mid-tropospheric high pressure area for the next couple of days, causing the cyclone to move on a northwestward to north-northwestward heading. Later in the forecast period, the global models build a weak ridge across the northern half of the Gulf of Mexico. This should induce the cyclone to turn westward or even a little south of west in 3-5 days. The latest NHC forecast lies between the simple and corrected dynamical model consensus predictions, TVCA and HCCA, and is quite similar to the previous official forecast.

At this time, the biggest threat from this slow-moving system is rain and flooding, particularly near and over mountainous terrain.

KEY MESSAGES:

  • 1. The system is expected to produce heavy rainfall that could result in life-threatening flash flooding over portions of the Yucatan Peninsula, far western Cuba and well away from the center in the Mexican states of Campeche, Tabasco, and northern Chiapas.
  • 2. The depression is forecast to become a tropical storm and bring tropical storm conditions to portions of the Yucatan Peninsula on Saturday, where a Tropical Storm Warning is in effect.
FORECAST POSITIONS AND MAX WINDS

INIT  02/2100Z 18.8N  85.3W   30 KT  35 MPH - Depression (WNW Mahahual, Mexico)
 12H  03/0600Z 19.5N  86.1W   35 KT  40 MPH - Tropical Storm (ESE Punta Allen, Mexico)
 24H  03/1800Z 20.5N  87.0W   40 KT  45 MPH - Tropical Storm (W Cozumel, Mexico)
 36H  04/0600Z 21.6N  87.5W   40 KT  45 MPH - Tropical Storm (WSW Holbox, Mexico)
 48H  04/1800Z 22.3N  87.7W   40 KT  45 MPH - Tropical Storm (WNW El Cayo, Mexico)
 60H  05/0600Z 22.5N  88.0W   45 KT  50 MPH - Tropical Storm (ENE Rio Lagartos, Mexico)
 72H  05/1800Z 22.5N  88.8W   50 KT  60 MPH - Tropical Storm (ENE Progreso, Mexico)
 96H  06/1800Z 22.5N  91.0W   50 KT  60 MPH - Tropical Storm (WNW Progreso, Mexico)
120H  07/1800Z 22.0N  92.5W   50 KT  60 MPH - Tropical Storm (WNW Celestún, Mexico)

NWS National Hurricane Center Miami FL 1100 AM EDT Fri Oct 02, 2020

Visible satellite images show that cloudiness and showers associated with the low-pressure area over the northwestern Caribbean Sea have become significantly better organized since yesterday, with convective banding features becoming prominent. Moreover, low cloud motions suggest that a closed circulation has become better defined. Therefore, advisories are being initiated on Tropical Depression Twenty-Five at this time.

The initial intensity estimate is 30 kt based on Dvorak T-numbers, but an Air Force Reserve Hurricane Hunter aircraft is scheduled to investigate the system later today to provide a better intensity estimate. Sea surface temperatures are very warm, near 30 deg C, and vertical shear should remain low for at least the next couple of days, so the cyclone is likely to become a tropical storm by the time it nears the Yucatan Peninsula tomorrow. The main impediment to strengthening over the next few days should be the interaction with land. Given the uncertainties about how far offshore the center will be over the next several days, the official intensity forecast is conservative.

Since there is still a lot of scatter in the center fixes, the initial motion estimate, 315/8 kt, is rather uncertain. For the next couple of days, the system is expected to move northwestward to north-northwestward on the southwestern edge of a mid-level high pressure area. This would take the center near or over the northeastern Yucatan Peninsula. After about 48 hours, the steering currents are not well-defined and there is considerable spread in the track models. At this time, it appears the cyclone should move slowly westward over the latter part of the forecast period in response to weak ridging over the north-central Gulf of Mexico. The official forecast is near or a little north of the corrected and simple model consensus predictions. Tropical Storm Warnings and Watches have been issued for a portion of the Yucatan Peninsula.

KEY MESSAGES:

  • 1. The system is expected to produce heavy rainfall that could result in life-threatening flash flooding over portions of the Yucatan Peninsula, far western Cuba and well away from the center in the Mexican states of Campeche, Tabasco, and northern Chiapas.
  • 2. The depression is forecast to become a tropical storm and bring tropical storm conditions to portions of the Yucatan Peninsula on Saturday, where a Tropical Storm Warning is in effect.
FORECAST POSITIONS AND MAX WINDS

INIT  02/1500Z 18.1N  84.7W   30 KT  35 MPH - Depression (WNW San Padro, Belize)
 12H  03/0000Z 18.9N  85.6W   30 KT  35 MPH - Depression (WSW Pulticub, Mexico)
 24H  03/1200Z 19.8N  86.6W   35 KT  40 MPH - Tropical Storm (WSW Cozumel, Mexico)
 36H  04/0000Z 20.6N  87.2W   40 KT  45 MPH - Tropical Storm (WSW Playa del Carmen, Mexico)
 48H  04/1200Z 21.4N  87.5W   40 KT  45 MPH - Tropical Storm (ENE Chiquilá, Mexico)
 60H  05/0000Z 22.0N  87.6W   40 KT  45 MPH - Tropical Storm (ENE El Cuyo, Mexico)
 72H  05/1200Z 22.0N  88.2W   45 KT  50 MPH - Tropical Storm (ENE Río Lagartos, Mexico)
 96H  06/1200Z 21.5N  90.5W   45 KT  50 MPH - Tropical Storm (WNW Sisal, Mexico)
120H  07/1200Z 21.5N  92.5W   45 KT  50 MPH - Tropical Storm (WNW Progreso, Mexico)

NWS National Hurricane Center Miami FL 800 PM EDT Thu Oct 1, 2020 

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

  • 1. A broad area of low pressure has developed over the west-central Caribbean Sea just north of the northeastern coast of Honduras. Satellite images indicate that showers and thunderstorms are slowly becoming better organized, and a NOAA buoy northeast of the center has reported winds to near tropical storm force during the past few hours. Environmental conditions are expected to be conducive for a tropical depression or a tropical storm to form on Friday or Saturday, but only if the system moves and remains over the waters of the northwestern Caribbean Sea or southern Gulf of Mexico. Development will become less likely if the system moves over the Yucatan Peninsula or northern Central America. Regardless of development, this system is expected to produce locally heavy rains, with possible flash flooding, over portions of southeastern Mexico, Central America, and western Cuba during the next several days, and interests in those areas should monitor the progress of this disturbance. An Air Force Reserve reconnaissance aircraft is scheduled to investigate the system tomorrow afternoon, if necessary. * Formation chance through 48 hours…high…70 percent. * Formation chance through 5 days…high…80 percent.

NWS National Hurricane Center Miami FL 200 PM EDT Thu Oct 1, 2020  

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

1. A well-defined tropical wave located over the western Caribbean Sea is producing a large area of disorganized showers and thunderstorms. Conditions are expected to be conducive for a tropical depression to form by early next week, but only if the system moves and remains over the waters of the northwestern Caribbean Sea or southern Gulf of Mexico. Development will become less likely if the system moves over the Yucatan Peninsula or northern Central America. Regardless of development, this system is expected to produce locally heavy rains, with possible flash flooding, over portions of southeastern Mexico, Central America, and western Cuba during the next several days, and interests in those areas should monitor the progress of the disturbance. * Formation chance through 48 hours…medium…40 percent. * Formation chance through 5 days…high…70 percent.

NWS National Hurricane Center Miami FL 800 AM EDT Thu Oct 1, 2020 

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

  • 1. A tropical wave located over the west-central Caribbean Sea is producing a large area of disorganized showers and thunderstorms. Conditions are expected to be conducive for development of this system, and a tropical depression is likely to form over the northwestern Caribbean Sea or the south-central Gulf of Mexico, possibly before the system reaches the east coast of the Yucatan Peninsula on Saturday. Interests in Belize, the Yucatan Peninsula of Mexico, and western Cuba should monitor the progress of this disturbance. * Formation chance through 48 hours…medium…40 percent. * Formation chance through 5 days…high...70 percent.

NWS National Hurricane Center Miami FL 800 PM EDT Wed Sep 30, 2020 

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

  • 1. A tropical wave located over the west-central Caribbean Sea is expected to continue moving westward over the next couple of days, and produce a broad area of low pressure over the western Caribbean Sea or extreme southern Gulf of Mexico by Thursday night or Friday. Environmental conditions are forecast to be conducive for some development thereafter, and a tropical depression could form over the weekend while the system moves slowly west-northwestward over the northwestern Caribbean Sea. Interests in Belize, the Yucatan Peninsula, and western Cuba should monitor the progress of this disturbance. * Formation chance through 48 hours…low…20 percent. * Formation chance through 5 days…high…70 percent.

NWS National Hurricane Center Miami FL 800 AM EDT Wed Sep 30, 2020

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

  • 1. A tropical wave located over the west-central Caribbean Sea is expected to move westward over the next couple of days and interact with a frontal system, producing a broad area of low pressure over the western Caribbean Sea by Thursday night or Friday. Environmental conditions are forecast to be conducive for some development thereafter, and a tropical depression could form over the weekend while the system moves slowly west-northwestward over the northwestern Caribbean Sea. * Formation chance through 48 hours…low…10 percent. * Formation chance through 5 days…medium…60 percent.

NWS National Hurricane Center Miami FL 800 PM EDT Tue Sep 29, 2020

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

  • 1. A tropical wave located over the central Caribbean Sea is expected to move westward over the next few days and interact with a frontal system, producing a broad area of low pressure over the western Caribbean Sea on Friday. Environmental conditions are forecast to be conducive for some additional development thereafter, and a tropical depression could form over the weekend while the system moves slowly west-northwestward over the northwestern Caribbean Sea. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…medium...60 percent.

NWS National Hurricane Center Miami FL 800 AM EDT Tue Sep 29, 2020

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

  • 1. A broad area of low pressure is expected to form over the western Caribbean Sea in a few days. Environmental conditions are forecast to be conducive for some development thereafter, and a tropical depression could form late this week or this weekend while the system moves slowly west-northwestward over the northwestern Caribbean Sea. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…medium…50 percent.

NWS National Hurricane Center Miami FL 200 PM EDT Mon Sep 28, 2020

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

  • 1. A broad area of low pressure is expected to form over the western Caribbean Sea in a few days. Environmental conditions are expected to be conducive for some gradual development thereafter, and a tropical depression could form late this week or this weekend while the system moves slowly west-northwestward over the northwestern Caribbean Sea. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…medium…40 percent.

NWS National Hurricane Center Miami FL 800 AM EDT Mon Sep 28, 2020

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

  • 1. A broad area of low pressure is expected to form over the western Caribbean Sea in a few days. Some gradual development of the disturbance will be possible thereafter while the system moves slowly west-northwestward over the northwestern Caribbean Sea. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low…30 percent.

NWS National Hurricane Center Miami FL 200 PM EDT Wed Sep 23 2020

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

The National Hurricane Center is issuing advisories on Post-Tropical Cyclone Teddy, located north of eastern Nova Scotia. The Weather Prediction Center is issuing advisories on Post-Tropical Cyclone Beta located inland near the Texas/Louisiana border.

NWS National Hurricane Center Miami FL 800 PM EDT Tue Sep 22, 2020

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

The National Hurricane Center is issuing advisories on Post-Tropical Cyclone Teddy, located a couple of hundred miles south of Halifax, Nova Scotia, and on Tropical Storm Paulette, located a few hundred miles east-southeast of the Azores. The Weather Prediction Center is issuing advisories on Tropical Depression Beta located just inland along the central Texas coast.

NWS National Hurricane Center Miami FL 200 PM EDT Tue Sep 22, 2020

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

The National Hurricane Center is issuing advisories on recently downgraded Tropical Depression Beta, located over the Texas coast, on Hurricane Teddy, located a few hundred miles south of Halifax, Nova Scotia, and on Tropical Storm Paulette, located a few hundred miles southeast of the Azores.

  • 1. Showers and thunderstorms extending from the southeastern Bahamas westward through Cuba and into the southeastern Gulf of Mexico are associated with a cold front. This system is forecast to move little for the next day or so, then move back northward on Thursday through Saturday. While development of this system over the southeastern Gulf of Mexico late this week is very unlikely, locally heavy rainfall is possible over portions of Cuba through Wednesday and over the Florida Keys and south Florida on Thursday and Friday. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low…10 percent.

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

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Video: Tropical Storm Gamma: Workers Clear Damage in Yucatan, Mexico