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Tropical Storm Grace Forecast Discussion Number 20
2021-08-18 10:52:16| National Hurricane Center (Atlantic)
Issued at 500 AM EDT Wed Aug 18 2021 000 WTNT42 KNHC 180852 TCDAT2 Tropical Storm Grace Discussion Number 20 NWS National Hurricane Center Miami FL AL072021 500 AM EDT Wed Aug 18 2021 An Air Force Reserve reconnaissance aircraft investigating Grace earlier this morning observed a peak 850-mb flight-level wind of 61 kt in the northeastern quadrant along with reliable SFMR surface wind speeds of 50-52 kt. The aircraft measured a central pressure of about 1000 mb, a reading that had been steady for about 3 hours. Those data were the basis for maintaining the 0600 UTC intensity at 50 kt. Since the last recon mission, however, deep convection has increased markedly over the low-level center, with cloud tops exceeding -75 deg C. Although the center is just inside the western edge of convective cloud canopy due to modest west-northwesterly vertical wind shear, Dvorak satellite intensity estimates from TAFB and SAB are a consensus T3.5/55 kt. These intensity estimates, along with the increase in convection over the center is the justification for increasing the 0900 UTC advisory intensity to 55 kt. Grace has been maintaining a steady course north of due west, or 280/14 kt for more than 18 hours. A strong deep-layer ridge to the north of the cyclone is expected to keep Grace moving in direction between west and west-northwest through the 96-hour forecast period. The latest NHC model guidance remain in strong agreement on Grace making landfall along the northeastern coast of the Yucatan Peninsula of Mexico shortly after the 24-hour forecast period, followed by a motion across the peninsula and emerging over the Bay of Campeche around 36 hours. Thereafter, the model guidance begins to diverge, with the HWRF, HMON, and COAMPS-TC regional models along the northern side of the guidance envelope, the GFS and UKMET global models down the middle, and the ECMWF model along the southern edge of the guidance suite. The new NHC forecast lies close to the previous advisory track and the consensus models TVCA and HCCA, which are a little south of the FSSE consensus model. Although the upper-level wind environment isn't ideal for rapid strengthening, it is conducive enough for steady strengthening to occur due to the flow forecast to be strongly diffluent. Sea-surface temperatures are expected to be near 30 deg C and the water is also deep and warm, which should prevent any cold upwelling from occurring beneath the cyclone. As a result, a peak intensity of 75 kt just prior to landfall has been carried over from the previous advisory, which is a little above all of the 0600 UTC intensity guidance. Although Grace will weaken substantially after passing over the Yucatan peninsula, restrengthening is expected over the warm waters of thew Bay of Campeche in the 48-72- hour period where the upper-level flow regime is forecast to be more conducive for intensification. Dissipation is now expected over the mountains of central Mexico by 120 hours. The NHC intensity forecast is in best agreement with the HCCA and IVCN consensus aids at 36 hours and beyond. Key Messages: 1. Hurricane conditions and a dangerous storm surge are expected over portions of the Hurricane Warning area in the eastern Yucatan Peninsula of Mexico beginning late tonight. 2. Over the next few days, heavy rainfall across the Cayman Islands as well as portions of the Yucatan Peninsula and Vera Cruz State should lead to flash and urban flooding. Mudslides will be possible in Jamaica. 3. Tropical storm conditions are expected over the Cayman Islands through this morning. Hurricane conditions are possible in the Cayman Islands later this morning. Tropical storm conditions are expected to spread westward from portions of the southern coast of Cuba in the warning area to, possibly, other portions of the southern coast of Cuba in the watch area today. FORECAST POSITIONS AND MAX WINDS INIT 18/0900Z 18.8N 80.9W 55 KT 65 MPH 12H 18/1800Z 19.3N 83.2W 60 KT 70 MPH 24H 19/0600Z 19.9N 86.4W 75 KT 85 MPH 36H 19/1800Z 20.3N 89.4W 50 KT 60 MPH...INLAND 48H 20/0600Z 20.6N 92.1W 50 KT 60 MPH...OVER WATER 60H 20/1800Z 20.7N 94.4W 65 KT 75 MPH 72H 21/0600Z 20.7N 96.8W 75 KT 85 MPH 96H 22/0600Z 20.6N 101.4W 35 KT 40 MPH...INLAND 120H 23/0600Z...DISSIPATED $$ Forecaster Stewart
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Tropical Storm Henri Forecast Discussion Number 9
2021-08-18 05:32:13| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Tue Aug 17 2021 000 WTNT43 KNHC 180331 CCA TCDAT3 Tropical Storm Henri Discussion Number 9...Corrected NWS National Hurricane Center Miami FL AL082021 1100 PM AST Tue Aug 17 2021 Corrected speed of motion in the second paragraph. Henri's appearance on satellite imagery has remained more or less steady-state, featuring a small CDO with additional convective banding along the eastern side of the circulation. However, the earlier mid-level eye feature that was trying to develop on radar from Bermuda has recently become more ill-defined, possibly due to some dry-air being entrained into the inner-core of the storm. The latest Dvorak subjective estimates from SAB and TAFB were T3.0/45 kt and T3.5/55 kt, respectively. In addition, a 2336 UTC ASCAT-A pass had lower peak wind retrievals than what was found earlier today, but this instrument may not be quite able to sample the relatively small tropical cyclone core observed on radar. For now, the initial intensity will be held at 55 kt, though this estimate could be a bit generous given the recent scatterometer data. Henri has begun a more pronounced motion to the west-southwest, and the latest initial motion is estimated at 255/07 kt. An amplified mid- to upper-tropospheric ridge located northwest of Henri is expected to keep the storm on a west-southwestward or westward heading in the short term. However this ridge will begin to gradually erode as an mid- to upper-level trough propagates eastward to the Eastern United States. This should allow Henri to start gaining latitude by 48 hours, turning toward the northwest, north, and then northeast as the mid-level ridging redevelops southeast of the cyclone. There remains a large amount of spread in the guidance, with the stronger regional hurricane models on the left side, while the weaker global models remain more on the right side of the guidance envelope. In general though, there was another westward shift in the guidance suite, so the latest NHC forecast track was adjusted again in that direction, and is in closest agreement to the HCCA guidance aid. The intensity forecast in the short-term is tricky. Last night and this morning, Henri's deep convection was been able to propagate into its up-shear quadrant, in spite of light to moderate northwesterly shear importing fairly dry mid-latitude air from the north. Consequently, the storm has been able to intensify and become more axis-symmetrical. Over the past few hours, however, the convection to the northwest of the center has eroded once again on Bermuda radar, likely due to dry air entrainment by the aforementioned vertical wind shear. On the other hand, the tropical cyclone is currently over sea-surface temperatures above 29 C, which will likely allow for significant boundary layer recovery of dry mid-level air that is able to get into the inner core. Thus, even as northerly vertical wind shear increases over the next 24 hours, Henri is expected to maintain its intensity. After 60 hours, this northerly shear is expected to subside, and Henri will have an opportunity to intensify towards the end of the forecast. The latest NHC intensity forecast is quite similar to the previous one for the first 60 hours, but is a little stronger in the latter time periods, blending the reliable HCCA guidance with the more aggressive regional hurricane models (HWRF, COAMPS-TC). FORECAST POSITIONS AND MAX WINDS INIT 18/0300Z 30.0N 65.1W 55 KT 65 MPH 12H 18/1200Z 29.9N 66.0W 60 KT 70 MPH 24H 19/0000Z 29.8N 67.7W 60 KT 70 MPH 36H 19/1200Z 29.8N 69.5W 60 KT 70 MPH 48H 20/0000Z 30.1N 71.1W 60 KT 70 MPH 60H 20/1200Z 30.9N 72.0W 60 KT 70 MPH 72H 21/0000Z 32.0N 71.9W 70 KT 80 MPH 96H 22/0000Z 36.6N 69.4W 80 KT 90 MPH 120H 23/0000Z 40.2N 65.0W 80 KT 90 MPH $$ Forecaster Papin/Brown
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Hurricane Linda Forecast Discussion Number 32
2021-08-18 04:55:11| Tropical Depression LIDIA
Issued at 500 PM HST Tue Aug 17 2021
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Tropical Storm Grace Forecast Discussion Number 19
2021-08-18 04:48:47| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Tue Aug 17 2021 009 WTNT42 KNHC 180248 TCDAT2 Tropical Storm Grace Discussion Number 19 NWS National Hurricane Center Miami FL AL072021 1100 PM EDT Tue Aug 17 2021 NOAA and Air Force Hurricane Hunter aircraft that have been investigating Grace this evening have found that the center moved off the western tip of Jamaica shortly before 0000 UTC. Radar and conventional satellite imagery, as well as earlier microwave data, show that convective banding has increased with a band that wraps around the eastern and northern portions of the circulation. The Air Force reconnaissance aircraft measured a peak 850-mb flight-level wind of 64 kt, and both aircraft have measured believable SFMR winds of 50-52 kt. Based on those data the maximum winds were increased to 50 kt on the 0000 UTC intermediate advisory, and the initial intensity remains unchanged for this advisory. Grace will be moving over the high ocean heat content waters of the northwestern Caribbean Sea during the next day or so. That, along with generally low to moderate vertical wind shear conditions, should allow for steady strengthening until Grace reaches the coast of the Yucatan Peninsula in just under 36 hours. The NHC intensity forecast call for Grace to become a hurricane on Wednesday, and the storm could peak near category 2 intensity before it reaches the coast of Mexico late Wednesday night or early Thursday. By the 36- hour forecast, some weakening is likely to have occurred as that point is now inland. Some weakening will likely occur while Grace moves over land, but restrengthening is predicted when the storm moves over the Bay of Campeche. The NHC intensity forecast is in best agreement with the HCCA and IVCN consensus aids. Grace has been moving slightly north of due west, or 280/12 kt. A strong deep-layer ridge the extends from the western Atlantic across the eastern and central Gulf of Mexico should continue to steer the tropical storm westward to west-northwestward for the next several days. While the dynamical models agree on this overall forecast scenario, there remains some north-south spread with the HWRF, HMON, and GFS along the northern side of the guidance envelope, taking Grace near the northeastern portion of the Yucatan Peninsula. On the other hand, the UKMET and its ensemble mean depict a more westward track toward the southern portion of the Yucatan Peninsula of Mexico. The NHC forecast splits these differences and lies near the various consensus aids, which were just a tad farther south this cycle. Key Messages: 1. Hurricane conditions and a dangerous storm surge are expected over portions of the Hurricane Warning area in the eastern Yucatan Peninsula of Mexico beginning late Wednesday night. 2. Heavy rainfall across Jamaica, the Cayman Islands, and the Yucatan Peninsula is likely to lead to flash and urban flooding. Mudslides are possible in Jamaica. 3. Tropical storm conditions are expected over portions of Jamaica for a few more hours, and over the Cayman Islands later tonight and Wednesday. Hurricane conditions are possible in the Cayman Islands by Wednesday morning. Tropical storm conditions are expected to spread westward from portions of the southern coast of Cuba in the warning area to, possibly, other portions of the southern coast of Cuba in the watch area tonight through Wednesday. FORECAST POSITIONS AND MAX WINDS INIT 18/0300Z 18.4N 79.2W 50 KT 60 MPH 12H 18/1200Z 18.9N 81.5W 60 KT 70 MPH 24H 19/0000Z 19.5N 84.7W 75 KT 85 MPH 36H 19/1200Z 20.0N 87.8W 80 KT 90 MPH...INLAND 48H 20/0000Z 20.4N 90.7W 50 KT 60 MPH...OVER WATER 60H 20/1200Z 20.7N 93.2W 65 KT 75 MPH 72H 21/0000Z 20.8N 95.6W 75 KT 85 MPH 96H 22/0000Z 20.7N 100.1W 35 KT 40 MPH...INLAND 120H 23/0000Z 20.5N 104.5W 20 KT 25 MPH...POST-TROP/INLAND $$ Forecaster Brown
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Tropical Storm Grace Forecast Discussion Number 18
2021-08-17 22:56:06| National Hurricane Center (Atlantic)
Issued at 500 PM EDT Tue Aug 17 2021 272 WTNT42 KNHC 172056 TCDAT2 Tropical Storm Grace Discussion Number 18 NWS National Hurricane Center Miami FL AL072021 500 PM EDT Tue Aug 17 2021 Radar imagery and earlier Hurricane Hunter aircraft and ASCAT observations indicate that the center of Grace has been moving over Jamaica. The aircraft and scatterometer data indicate that the maximum winds are near 45 kt. Cirrus-level outflow from the system remains quite pronounced, suggestive of weak vertical shear at this time. Grace will be moving over the waters of the northwestern Caribbean Sea beginning later tonight. These waters are of very high oceanic heat content. Although mid-level environmental humidities are shown by the SHIPS diagnoses to be only marginally moist for the next couple of days, other factors should be conducive for strengthening. The official intensity forecast, which shows Grace becoming a hurricane tomorrow, is in reasonable agreement with the latest multi-model consensus. Some slight weakening should occur due to passage over the Yucatan Peninsula, followed by re-intensification over the Bay of Campeche. There is, however, significant uncertainty in the intensity prediction for this latter part of the forecast period. The storm continues on a heading just north of west, or 280/13 kt. A strong 500-mb ridge should be maintained to the north of Grace for essentially the entire forecast period. There is good agreement among the track models on a continued generally westward to west-northwestward motion for the next 5 days. Little change has been made to the official track forecast in comparison to the previous one. The new NHC track is, again, very close to the dynamical model consensus. Key Messages: 1. Hurricane conditions and a dangerous storm surge are expected over portions of the Hurricane Warning area in the eastern Yucatan Peninsula of Mexico late Wednesday night. 2. Heavy rainfall across Haiti, Cuba, Jamaica, the Cayman Islands, and the Yucatan Peninsula is likely to cause to flash, urban, and small stream flooding, with the potential for mudslides highest in Haiti. 3. Tropical storm conditions are expected over portions of Jamaica through this evening, and over the Cayman Islands tonight and early Wednesday. Tropical storm conditions are expected to spread westward from portions of the southern coast of Cuba in the warning area to, possibly, other portions of the southern coast of Cuba in the watch area tonight through Wednesday. FORECAST POSITIONS AND MAX WINDS INIT 17/2100Z 18.4N 77.9W 45 KT 50 MPH 12H 18/0600Z 18.9N 80.3W 60 KT 70 MPH 24H 18/1800Z 19.4N 83.4W 70 KT 80 MPH 36H 19/0600Z 20.0N 86.7W 75 KT 85 MPH 48H 19/1800Z 20.5N 89.7W 60 KT 70 MPH...INLAND 60H 20/0600Z 20.9N 92.2W 65 KT 75 MPH...OVER WATER 72H 20/1800Z 21.2N 94.8W 75 KT 85 MPH 96H 21/1800Z 21.0N 99.5W 40 KT 45 MPH...INLAND 120H 22/1800Z 21.0N 103.0W 20 KT 25 MPH...POST-TROP/INLAND $$ Forecaster Pasch
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