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Tropical Storm Gamma Forecast Discussion Number 12
2020-10-05 10:50:29| National Hurricane Center (Atlantic)
Issued at 400 AM CDT Mon Oct 05 2020 000 WTNT45 KNHC 050850 TCDAT5 Tropical Storm Gamma Discussion Number 12 NWS National Hurricane Center Miami FL AL252020 400 AM CDT Mon Oct 05 2020 Gamma is a strongly sheared tropical storm that has been meandering just north of the northern coast of the Yucatan Peninsula of Mexico. Strong convective cloud tops colder than -80 deg C are located more than 60 nmi north and northeast of the well-defined and fully exposed low-level circulation center. An Air Force Reserve reconnaissance aircraft investigating the cyclone found maximum 850-mb flight-level winds of only 44 kt along with peak SFMR surface winds of 47 kt. In addition, a 0329Z ASCAT-A pass revealed peak surface winds of 41 kt. Allowing for undersampling by the scatterometer instrument and blending it with the SFMR winds supports lowering the initial intensity to 45 kt. The central pressure of 999 mb is based on a center dropsonde reports of 1000 mb and 10-12 kt winds. The initial motion estimate is an uncertain 240/02 kt. Gamma's future track remains highly uncertain after day 2. For the next 48 hours or so, the cyclone is forecast to move slowly southwestward to west-southwestward and weaken due to strong southerly vertical wind shear. Thereafter, TD-26 to the east is forecast to strengthen into a hurricane, accompanied by a corresponding increase in the size of that cyclone's circulation, which is expected to result in some binary interaction between the two tropical cyclones. Due to Gamma's expected smaller size on days 3 and 4, the cyclone is forecast to be pulled eastward and then northward, making landfall on and then moving over the northwestern Yucatan Peninsula. By day 5, Gamma is expected to degenerate into a remnant low and then be absorbed by the larger circulation of the expected central Gulf of Mexico hurricane that is currently TD-26. The new NHC track forecast is similar to but a little slower than the previous advisory track, and lies close to the southern edge of the guidance envelope. Strong southerly wind shear, combined with drier and more stable air just to the west of Gamma, is expected to weaken the cyclone further over the next few days. If land interaction occurs sooner than expected, then the cyclone could weaken and dissipate sooner than currently forecast. For now, the intensity forecast maintains continuity with the previous advisory and shows dissipation by 120 hours as Gamma interacts with what is expected to be a significant hurricane over the central Gulf of Mexico by 96 hours, which could end up absorbing the smaller Gamma tropical cyclone. 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 model intensity and track forecasts. 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 05/0900Z 22.7N 87.5W 45 KT 50 MPH 12H 05/1800Z 22.5N 88.0W 40 KT 45 MPH 24H 06/0600Z 22.1N 88.9W 40 KT 45 MPH 36H 06/1800Z 21.4N 89.8W 35 KT 40 MPH 48H 07/0600Z 20.8N 90.4W 35 KT 40 MPH 60H 07/1800Z 20.3N 90.5W 30 KT 35 MPH...INLAND YUCATAN 72H 08/0600Z 20.7N 90.1W 30 KT 35 MPH...INLAND YUCATAN 96H 09/0600Z 22.5N 90.0W 30 KT 35 MPH...OVER WATER 120H 10/0600Z...DISSIPATED $$ Forecaster Stewart
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Tropical Depression Twenty-six Forecast Advisory Number 3
2020-10-05 10:49:24| National Hurricane Center (Atlantic)
Issued at 0900 UTC MON OCT 05 2020 604 WTNT21 KNHC 050849 TCMAT1 TROPICAL DEPRESSION TWENTY-SIX FORECAST/ADVISORY NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL AL262020 0900 UTC MON OCT 05 2020 CHANGES IN WATCHES AND WARNINGS WITH THIS ADVISORY... NONE. SUMMARY OF WATCHES AND WARNINGS IN EFFECT... A HURRICANE WATCH IS IN EFFECT FOR... * CUBAN PROVINCES OF PINAR DEL RIO AND ARTEMISA * ISLE OF YOUTH A TROPICAL STORM WARNING IS IN EFFECT FOR... * CAYMAN ISLANDS INCLUDING LITTLE CAYMAN AND CAYMAN BRAC A TROPICAL STORM WATCH IS IN EFFECT FOR... * CUBA PROVINCE OF LA HABANA A HURRICANE WATCH MEANS THAT HURRICANE CONDITIONS ARE POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 48 HOURS. A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE EXPECTED SOMEWHERE WITHIN THE WARNING AREA WITHIN 36 HOURS. A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 48 HOURS. TROPICAL DEPRESSION CENTER LOCATED NEAR 17.0N 78.2W AT 05/0900Z POSITION ACCURATE WITHIN 30 NM PRESENT MOVEMENT TOWARD THE WEST-NORTHWEST OR 290 DEGREES AT 8 KT ESTIMATED MINIMUM CENTRAL PRESSURE 1006 MB MAX SUSTAINED WINDS 30 KT WITH GUSTS TO 40 KT. WINDS AND SEAS VARY GREATLY IN EACH QUADRANT. RADII IN NAUTICAL MILES ARE THE LARGEST RADII EXPECTED ANYWHERE IN THAT QUADRANT. REPEAT...CENTER LOCATED NEAR 17.0N 78.2W AT 05/0900Z AT 05/0600Z CENTER WAS LOCATED NEAR 16.9N 77.8W FORECAST VALID 05/1800Z 17.4N 79.1W MAX WIND 35 KT...GUSTS 45 KT. 34 KT... 40NE 40SE 40SW 0NW. FORECAST VALID 06/0600Z 18.6N 80.8W MAX WIND 45 KT...GUSTS 55 KT. 34 KT... 50NE 40SE 30SW 40NW. FORECAST VALID 06/1800Z 20.5N 83.3W MAX WIND 60 KT...GUSTS 75 KT. 50 KT... 30NE 20SE 0SW 30NW. 34 KT... 60NE 60SE 40SW 60NW. FORECAST VALID 07/0600Z 22.5N 85.8W MAX WIND 70 KT...GUSTS 85 KT. 64 KT... 15NE 15SE 0SW 15NW. 50 KT... 30NE 30SE 20SW 30NW. 34 KT... 70NE 60SE 50SW 70NW. FORECAST VALID 07/1800Z 24.4N 88.1W MAX WIND 80 KT...GUSTS 100 KT. 50 KT... 40NE 40SE 20SW 40NW. 34 KT... 90NE 70SE 50SW 80NW. FORECAST VALID 08/0600Z 25.9N 90.0W MAX WIND 90 KT...GUSTS 110 KT. 50 KT... 50NE 40SE 30SW 50NW. 34 KT...110NE 90SE 60SW 100NW. EXTENDED OUTLOOK. NOTE...ERRORS FOR TRACK HAVE AVERAGED NEAR 150 NM ON DAY 4 AND 175 NM ON DAY 5...AND FOR INTENSITY NEAR 15 KT EACH DAY OUTLOOK VALID 09/0600Z 28.0N 91.0W MAX WIND 85 KT...GUSTS 105 KT. OUTLOOK VALID 10/0600Z 32.4N 88.7W...INLAND MAX WIND 55 KT...GUSTS 65 KT. REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 17.0N 78.2W INTERMEDIATE PUBLIC ADVISORY...WTNT31 KNHC/MIATCPAT1...AT 05/1200Z NEXT ADVISORY AT 05/1500Z $$ FORECASTER STEWART
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Tropical Storm Marie Forecast Discussion Number 25
2020-10-05 10:32:24| National Hurricane Center (East Pacific)
Issued at 200 AM PDT Mon Oct 05 2020 000 WTPZ43 KNHC 050832 TCDEP3 Tropical Storm Marie Discussion Number 25 NWS National Hurricane Center Miami FL EP182020 200 AM PDT Mon Oct 05 2020 Satellite images show the exposed low-level circulation well to the southwest of any remaining deep convection. ASCAT data, however, came in at 50-55 kt just before 06Z, which is higher than the satellite presentation alone would suggest. The initial wind speed is set to 55 kt on the basis of that data. Marie should weaken during the next few days due to cold waters and strong shear. Models are in very good agreement on a steady weakening, and little change was made to the previous forecast. Remnant low status is expected by 48 hours, and could even happen sooner based on current trends. The storm is moving west-northwestward at about 8 kt this morning. A ridge to the north should steer Marie to the northwest or west-northwest for the next couple of days, then the tropical cyclone is likely to turn westward as it becomes a more shallow feature. Model guidance has generally been adjusting to this scenario, with a mid-latitude trough no longer expected to exert much influence. The new forecast is shifted southward from 48 hours and beyond, near but a little slower than the model consensus. FORECAST POSITIONS AND MAX WINDS INIT 05/0900Z 20.8N 131.1W 55 KT 65 MPH 12H 05/1800Z 21.2N 132.2W 45 KT 50 MPH 24H 06/0600Z 21.8N 133.6W 35 KT 40 MPH 36H 06/1800Z 22.4N 135.2W 30 KT 35 MPH 48H 07/0600Z 22.9N 136.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 60H 07/1800Z 23.2N 137.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 08/0600Z 23.2N 138.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 09/0600Z 23.0N 140.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 10/0600Z...DISSIPATED $$ Forecaster Blake
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Tropical Storm Marie Forecast Advisory Number 25
2020-10-05 10:30:26| National Hurricane Center (East Pacific)
Issued at 0900 UTC MON OCT 05 2020 000 WTPZ23 KNHC 050830 TCMEP3 TROPICAL STORM MARIE FORECAST/ADVISORY NUMBER 25 NWS NATIONAL HURRICANE CENTER MIAMI FL EP182020 0900 UTC MON OCT 05 2020 THERE ARE NO COASTAL WATCHES OR WARNINGS IN EFFECT. TROPICAL STORM CENTER LOCATED NEAR 20.8N 131.1W AT 05/0900Z POSITION ACCURATE WITHIN 30 NM PRESENT MOVEMENT TOWARD THE WEST-NORTHWEST OR 295 DEGREES AT 8 KT ESTIMATED MINIMUM CENTRAL PRESSURE 993 MB MAX SUSTAINED WINDS 55 KT WITH GUSTS TO 65 KT. 50 KT....... 50NE 40SE 0SW 60NW. 34 KT.......110NE 100SE 80SW 110NW. 12 FT SEAS..210NE 150SE 180SW 210NW. WINDS AND SEAS VARY GREATLY IN EACH QUADRANT. RADII IN NAUTICAL MILES ARE THE LARGEST RADII EXPECTED ANYWHERE IN THAT QUADRANT. REPEAT...CENTER LOCATED NEAR 20.8N 131.1W AT 05/0900Z AT 05/0600Z CENTER WAS LOCATED NEAR 20.6N 130.7W FORECAST VALID 05/1800Z 21.2N 132.2W MAX WIND 45 KT...GUSTS 55 KT. 34 KT...110NE 90SE 80SW 110NW. FORECAST VALID 06/0600Z 21.8N 133.6W MAX WIND 35 KT...GUSTS 45 KT. 34 KT...100NE 80SE 70SW 100NW. FORECAST VALID 06/1800Z 22.4N 135.2W MAX WIND 30 KT...GUSTS 40 KT. FORECAST VALID 07/0600Z 22.9N 136.5W...POST-TROP/REMNT LOW MAX WIND 30 KT...GUSTS 40 KT. FORECAST VALID 07/1800Z 23.2N 137.6W...POST-TROP/REMNT LOW MAX WIND 25 KT...GUSTS 35 KT. FORECAST VALID 08/0600Z 23.2N 138.5W...POST-TROP/REMNT LOW MAX WIND 25 KT...GUSTS 35 KT. EXTENDED OUTLOOK. NOTE...ERRORS FOR TRACK HAVE AVERAGED NEAR 100 NM ON DAY 4 AND 150 NM ON DAY 5...AND FOR INTENSITY NEAR 15 KT EACH DAY OUTLOOK VALID 09/0600Z 23.0N 140.0W...POST-TROP/REMNT LOW MAX WIND 20 KT...GUSTS 30 KT. OUTLOOK VALID 10/0600Z...DISSIPATED REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 20.8N 131.1W NEXT ADVISORY AT 05/1500Z $$ FORECASTER BLAKE
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Tropical Storm Gamma Forecast Discussion Number 11
2020-10-05 04:39:22| National Hurricane Center (Atlantic)
Issued at 1000 PM CDT Sun Oct 04 2020 000 WTNT45 KNHC 050239 TCDAT5 Tropical Storm Gamma Discussion Number 11 NWS National Hurricane Center Miami FL AL252020 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 12H 05/1200Z 22.7N 87.7W 45 KT 50 MPH 24H 06/0000Z 22.3N 88.5W 45 KT 50 MPH 36H 06/1200Z 21.8N 89.5W 40 KT 45 MPH 48H 07/0000Z 21.3N 90.3W 40 KT 45 MPH 60H 07/1200Z 20.3N 90.7W 35 KT 40 MPH 72H 08/0000Z 20.2N 90.1W 30 KT 35 MPH...INLAND 96H 09/0000Z 22.0N 90.7W 30 KT 35 MPH...OVER WATER 120H 10/0000Z 24.0N 91.0W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Zelinsky
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