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Tropical Storm Laura Forecast Discussion Number 10
2020-08-22 11:26:38| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sat Aug 22 2020 000 WTNT43 KNHC 220926 CCA TCDAT3 Tropical Storm Laura Discussion Number 10...Corrected NWS National Hurricane Center Miami FL AL132020 500 AM AST Sat Aug 22 2020 Corrected status at 96 and 120 h Surface observations and Doppler radar data from Puerto Rico indicate that the center of Laura is currently over the Virgin Islands, eastern Puerto Rico, and the adjacent Caribbean waters. Overall, the system has become a little better organized since the last advisory, with strong convection forming not far from the center to the east and southeast and a somewhat better defined circulation. However, the central area of light winds is quite large, and there is evidence of several vorticity centers rotating around the mean storm center. Earlier scatterometer data suggested that the maximum winds had decreased to 35 kt, and that is the initial intensity for this advisory. The initial motion is a somewhat uncertain 280/18. There is no change in the track forecast philosophy, as a subtropical ridge over the central and western Atlantic is expected to expand westward, causing Laura to move quickly west-northwestward for the next 3 days or so. After that, the storm should turn northwestward toward the western edge of the ridge over the northern Gulf coast. While the dynamical models are in good agreement with the general scenario, there is an unusual amount of cross track spread. The track guidance is spread from the Florida Keys to the western end of Cuba as the storm enters the Gulf of Mexico, and the models have potential landfall locations along the Gulf coast from the Florida Panhandle to the middle Texas coast. One complicating factor is the potential for interaction with Tropical Storm Marco, although at this time the model guidance suggests the storms will stay far enough apart to prevent direct interaction. The new forecast track is similar to the previous track through 72 hr, then it is shifted a bit to the west after that time. The new track lies near the various consensus models. Laura is moving into an environment of light shear, and combined with the somewhat improved organization it suggests the storm should strengthen. However, the forecast track takes the center over Hispaniola and then down the length of Cuba, which should at least slow any intensification. This is reflected in the new intensity forecast which shows slow strengthening. Over the Gulf of Mexico, warm water and a likely favorable shear environment should allow Laura to become a hurricane, a scenario now supported by much of the guidance. Key Messages: 1. Tropical storm conditions are expected across portions of the northern Leeward Islands, the Virgin Islands, and Puerto Rico through today. Tropical storm conditions are also expected along the northern coasts of the Dominican Republic and Haiti, and the Turks and Caicos and southeastern Bahamas Saturday into Sunday. Heavy rainfall is likely across these areas beginning and could cause mudslides and flash and urban flooding through Sunday. 2. Tropical storm conditions are possible over portions of the central Bahamas Sunday night, as well as portions of eastern and central Cuba Sunday and Sunday night. 3. The details of the long-range track and intensity forecasts remain more uncertain than usual since Laura is forecast to move near or over portions of the Greater Antilles through Monday. However, Laura could bring storm surge, rainfall, and wind impacts to portions of Cuba, the Bahamas, and Florida early next week and the northern U.S. Gulf Coast by the middle of next week. Interests there should monitor the progress of Laura and updates to the forecast during the next few days. FORECAST POSITIONS AND MAX WINDS INIT 22/0900Z 17.6N 65.5W 35 KT 40 MPH 12H 22/1800Z 18.2N 67.7W 40 KT 45 MPH 24H 23/0600Z 19.1N 71.0W 40 KT 45 MPH...INLAND 36H 23/1800Z 20.3N 74.6W 45 KT 50 MPH...INLAND 48H 24/0600Z 21.6N 78.3W 45 KT 50 MPH...INLAND 60H 24/1800Z 23.1N 81.8W 45 KT 50 MPH...INLAND 72H 25/0600Z 24.6N 84.7W 55 KT 65 MPH...OVER WATER 96H 26/0600Z 27.5N 89.5W 75 KT 85 MPH 120H 27/0600Z 31.0N 92.0W 55 KT 65 MPH...INLAND $$ Forecaster Beven
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Tropical Storm Marco Forecast Discussion Number 8
2020-08-22 10:50:42| National Hurricane Center (Atlantic)
Issued at 400 AM CDT Sat Aug 22 2020 000 WTNT44 KNHC 220850 TCDAT4 Tropical Storm Marco Discussion Number 8 NWS National Hurricane Center Miami FL AL142020 400 AM CDT Sat Aug 22 2020 SFMR data from the last leg of the 53rd Air Force Reserve reconnaissance aircraft indicated a couple of 48-50 kt winds, but were associated with a significant spike in the rainfall rate. Additionally, the flight-level winds were only 36 kt in that area and the central pressure has increased a little to 1005 mb. The cloud pattern has improved during the past several hours with deep convection developing near the center and spiral bands forming over the eastern portion of cyclone. Based on a blend the hurricane hunter data and current subjective satellite intensity estimates, the initial intensity is raised to 40 kt. Although the UW-CIMSS shear product and global models indicate a favorable upper wind pattern, GOES-16 sounder analysis data show a higher than normal vertically stable environment in the western Caribbean. This negative contribution maybe what's hampering significant development. Consequently, as shown in the previous advisory, only modest strengthening is indicated in the NHC forecast through 48 hours. Only the Decay SHIPS and LGEM intensity models indicate that Marco will become a hurricane in a couple of days. Both the HMON and HWRF have backed off of showing a hurricane in the Gulf. Afterward, increasing west-southwesterly shear should lead to weakening as the cyclone turns toward the northwestern Gulf coast. The NHC forecast lies between the higher LGEM/Decay SHIPS solution and the lower NOAA HCCA intensity model which indicates a peak intensity of 55 kt. The initial motion is estimated to be west-northwestward, or 335/10 kt. Marco is being steered toward the northwest by a mid- to upper-level cut-off low and associated trough extending into the southwestern Gulf from the Mississippi Valley. By Sunday, the aforementioned feature is forecast to lift northeastward allowing the subtropical ridge to build back over the central gulf. This should cause Marco to turn northwestward and west-northwestward early next week toward the the northwestern Gulf coast. Large-scale guidance generally agree that any binary direct or indirect interaction, while both systems are in the gulf and at near equal latitude, is unlikely at this point. The official track forecast has been adjusted to the right of the previous advisory and lies just to the left of the various multi-model consensus aids. The 34 kt wind radii have been adjusted based on the aircraft reconnaissance data and a 0224 UTC scatterometer pass. Key Messages: 1. Marco is forecast to strengthen over the northwestern Caribbean Sea through Saturday as it approaches the northeast coast of the Yucatan Peninsula. A Hurricane Watch and a Tropical Storm Warning are in effect for portions of that region. 2. The system is expected to move into the south-central Gulf of Mexico as a tropical storm on Sunday. Although some strengthening is anticipated on Sunday, weakening is forecast as the system approaches the northwestern Gulf coast on Tuesday. It is still too soon to know exactly the location and magnitude of impacts the system will produce along the central or northwestern Gulf Coast, and interests in that area should continue monitoring the progress of this system over the next few days. FORECAST POSITIONS AND MAX WINDS INIT 22/0900Z 19.6N 85.4W 40 KT 45 MPH 12H 22/1800Z 20.9N 86.1W 45 KT 50 MPH 24H 23/0600Z 22.5N 87.1W 50 KT 60 MPH 36H 23/1800Z 24.1N 88.3W 55 KT 65 MPH 48H 24/0600Z 25.7N 89.9W 60 KT 70 MPH 60H 24/1800Z 27.3N 91.3W 55 KT 65 MPH 72H 25/0600Z 28.3N 93.4W 50 KT 60 MPH 96H 26/0600Z 29.1N 96.2W 40 KT 45 MPH...INLAND 120H 27/0600Z 29.6N 97.8W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Roberts
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Tropical Storm Laura Forecast Discussion Number 9
2020-08-22 04:54:37| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Fri Aug 21 2020 000 WTNT43 KNHC 220254 TCDAT3 Tropical Storm Laura Discussion Number 9 NWS National Hurricane Center Miami FL AL132020 1100 PM AST Fri Aug 21 2020 Laura remains quite disorganized this evening. Although satellite and radar images show a fair amount of deep convection over and to the east of the northern Leeward Islands, NOAA Hurricane Hunter data and surface observations indicate that the low-level center is located well to the west of the main area of deep convection. This asymmetric structure indicates that Laura is still not vertically aligned due to at least moderate wind shear. The initial intensity is held at a possibly generous 40 kt, and most of the strongest winds are well north and east of the center. The steering pattern for Laura appears to be very well established. A subtropical ridge over the central and western Atlantic is expected to expand westward, and that should cause Laura to move west-northwestward at a fairly quick pace during the next few days. This should take the storm across Puerto Rico on Saturday, near Hispaniola Saturday night, and close to or over Cuba on Sunday and Monday. By early next week, Laura should approach the western end of the ridge and that should cause the storm to slow down and turn toward the northwest over the eastern and central Gulf of Mexico. Even though the steering pattern is well established, there are still chances of center reformations, which could cause small but important track changes. The NHC track forecast has been adjusted a little to the south of the previous one to account for the more southern initial position and westward motion. Near the end of the period, Laura's track could also be influenced by Tropical Storm Marco, which is also forecast to be over the Gulf of Mexico, however the details of that interaction are highly uncertain at this time. Although the storm's structure is quite ragged at the moment, some of the models do show Laura becoming better organized this weekend and early next week due to a decrease in wind shear and very warm waters. However, there is significant uncertainty on how much the circulation will interact with the rugged islands of Hispaniola and Cuba. If the storm is able to stay north of those islands, some notable strengthening is possible as depicted by the HWRF and HMON models. However, if the storm moves over the islands, it might not strengthen at all until it passes through that area. The bottom line is the intensity forecast is very track dependent, which makes it more uncertain than normal. Given that the new track shows more land interaction, this forecast shows less strengthening in the short term, but is largely unchanged at the longer forecast times. Key Messages: 1. Tropical storm conditions are expected across portions of the northern Leeward Islands, the Virgin Islands, and Puerto Rico through Saturday. Tropical storm conditions are also expected along the northern coasts of the Dominican Republic and Haiti, and the Turks and Caicos and southeastern Bahamas Saturday into Sunday. Heavy rainfall is likely across these areas beginning and could cause mudslides and flash and urban flooding through Sunday. 2. Tropical storm conditions are possible over portions of the central Bahamas Sunday night. 3. The details of the long-range track and intensity forecasts remain more uncertain than usual since Laura is forecast to move near or over portions of the Greater Antilles through Monday. However, Laura could bring storm surge, rainfall, and wind impacts to portions of Cuba, the Bahamas, and Florida early next week and the northern U.S. Gulf Coast by the middle of next week. Interests there should monitor the progress of Laura and updates to the forecast during the next few days. FORECAST POSITIONS AND MAX WINDS INIT 22/0300Z 17.0N 63.5W 40 KT 45 MPH 12H 22/1200Z 17.6N 65.9W 40 KT 45 MPH 24H 23/0000Z 18.4N 69.3W 40 KT 45 MPH...INLAND 36H 23/1200Z 19.5N 72.8W 40 KT 45 MPH...INLAND 48H 24/0000Z 20.8N 76.4W 45 KT 50 MPH...INLAND 60H 24/1200Z 22.1N 80.1W 45 KT 50 MPH...INLAND 72H 25/0000Z 23.8N 83.3W 55 KT 65 MPH...OVER WATER 96H 26/0000Z 26.5N 87.7W 65 KT 75 MPH...OVER WATER 120H 27/0000Z 29.2N 90.2W 65 KT 75 MPH...OVER WATER $$ Forecaster Cangialosi
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Tropical Storm Marco Forecast Discussion Number 7
2020-08-22 04:54:37| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Fri Aug 21 2020 000 WTNT44 KNHC 220254 TCDAT4 Tropical Storm Marco Discussion Number 7 NWS National Hurricane Center Miami FL AL142020 1100 PM EDT Fri Aug 21 2020 An Air Force Reserve Hurricane Hunter aircraft has investigated the system over the northwest Caribbean during the past few hours. The plane reported a number of unflagged SFMR winds between 35 and 40 kt and max flight level winds of 41 kt. A blend of these data supports an intensity of 35 kt, and therefore, this system has been designated as Tropical Storm Marco. Deep convection has increased near and to the east of Marco's center during the past few hours. Although there still isn't much evidence of inner-core banding, the data from the plane does indicate that the center of Marco has become better defined since the afternoon and that the minimum pressure has dropped. Unfortunately the intensity forecast has not become any clearer and confidence in that aspect of the forecast is quite low. Marco is embedded within an environment that could support a fast rate of strengthening. However, recent microwave data does not indicate that the system has developed an inner-core, and only gradual strengthening is likely until it does. The intensity guidance spread is quite high, with the GFS and ECMWF global models both showing little further strengthening, while the HMON regional model rapidly makes Marco a hurricane before it reaches the northeast tip of the Yucatan peninsula. That possibility can not be ruled out, but a majority of the intensity guidance favors the weaker solution of the global models. Even with the HMON outlier included, the NHC intensity forecast is above the model consensus. Once Marco moves over the central Gulf of Mexico, a rapid increase in wind shear associated with an upper-level trough should limit the potential for further strengthening, and weakening is still anticipated before Marco nears the northern Gulf Coast, as shown in the previous official forecast. Confidence in the track forecast is also lower than normal, as the models spread remains quite high. Only small adjustments were made to the NHC forecast which heavily favors the GFS and ECMWF solutions on the left side of the track guidance. It is worth noting that the NHC track forecast is near middle of the GFS and ECMWF ensembles. Marco is currently forecast to move northwestward toward a weakness in the subtropical ridge over the central Gulf of Mexico for the next day or two, before the ridge builds and turns the tropical cyclone farther west. Near the end of the period, Marco's track and intensity could be also influenced by Tropical Storm Laura which is also forecast to be over the Gulf of Mexico, however the details of that interaction are highly uncertain at this time. Given the high uncertainty in the forecast, larger than normal changes could be required to future advisories. Key Messages: 1. Marco is forecast to strengthen over the northwestern Caribbean Sea through Saturday as it approaches the northeast coast of the Yucatan Peninsula. A Hurricane Watch and a Tropical Storm Warning are in effect for portions of that region. 2. The system is expected to move into the south-central Gulf of Mexico as a tropical storm on Sunday. Although some strengthening is anticipated on Sunday, weakening is forecast as the system approaches the northwestern Gulf coast on Tuesday. It is still too soon to know exactly the location and magnitude of impacts the system will produce along the central or northwestern Gulf Coast, and interests in that area should continue monitoring the progress of this system over the next few days. FORECAST POSITIONS AND MAX WINDS INIT 22/0300Z 18.7N 84.9W 35 KT 40 MPH 12H 22/1200Z 19.7N 85.7W 45 KT 50 MPH 24H 23/0000Z 21.1N 86.7W 50 KT 60 MPH 36H 23/1200Z 22.7N 88.0W 55 KT 65 MPH 48H 24/0000Z 24.4N 89.5W 60 KT 70 MPH 60H 24/1200Z 25.9N 91.0W 60 KT 70 MPH 72H 25/0000Z 27.5N 92.8W 60 KT 70 MPH 96H 26/0000Z 29.0N 95.4W 45 KT 50 MPH...INLAND 120H 27/0000Z 30.0N 97.4W 30 KT 35 MPH...INLAND $$ Forecaster Zelinsky
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Tropical Storm Laura Forecast Discussion Number 8
2020-08-21 23:25:29| National Hurricane Center (Atlantic)
Issued at 500 PM AST Fri Aug 21 2020 000 WTNT43 KNHC 212125 CCB TCDAT3 Tropical Storm Laura Discussion Number 8...Corrected NWS National Hurricane Center Miami FL AL132020 500 PM AST Fri Aug 21 2020 Corrected formatting and initial intensity A poorly-defined convective band has become evident over the southeastern portion of the circulation. However, there is little or no deep convection near the estimated center. Overall, the system's cloud pattern still has a ragged appearance. Dvorak intensity estimates range from 35 to 45 kt, and the current intensity is held at 40 knots based on continuity from Hurricane Hunter observations from earlier today. There is a fairly well-defined upper-level outflow pattern at this time, but an upper-level trough to the west of Laura could be an impediment to future strengthening. The official intensity forecast is a little below the intensity consensus mainly due to the influences of the land masses of the Greater Antilles. At days 4-5, the intensity forecast is also a bit below the consensus due to uncertainties at these longer forecast ranges. The center is not very easy to see, even on visible or radar images, but the best guess at an initial motion is 275/15 kt. The track forecast reasoning has not changed much from the previous advisory package. Laura should move generally west-northwestward along the southern periphery of a subtropical ridge for about the next 72 hours. Later in the forecast period, the cyclone is expected to turn northwestward as it begins to move around the western side of the ridge. The track guidance has shifted westward at days 4-5 and so has the official forecast, which is mostly close to the model consensus, but not quite as far west as that guidance in the latter part of the forecast period. Another NOAA Hurricane Hunter Aircraft is scheduled to investigate Laura shortly. KEY MESSAGES: 1. Tropical storm conditions are expected across portions of the northern Leeward Islands, the Virgin Islands, and Puerto Rico today through Saturday, Tropical Storm conditions are also expected along the northern coasts of the Dominican Republic and Haiti from Saturday into Sunday. Heavy rainfall is likely across these areas beginning today and could cause mudslides and flash and urban flooding through Sunday. 2. Tropical storm conditions are possible over portions of the southeastern Bahamas and the Turks and Caicos Islands on Sunday. 3. The details of the long-range track and intensity forecasts remain more uncertain than usual since Laura is forecast to move near or over Portions of the Greater Antilles through Monday. However, Laura could bring storm surge, rainfall, and wind impacts to portions of Cuba, the Bahamas, and Florida early next week and the northern U.S. Gulf Coast by the middle of next week. Interests there should monitor the progress of Laura and updates to the forecast during the next few days. FORECAST POSITIONS AND MAX WINDS INIT 21/2100Z 17.1N 61.2W 40 KT 45 MPH 12H 22/0600Z 17.7N 63.9W 40 KT 45 MPH 24H 22/1800Z 18.6N 67.3W 45 KT 50 MPH 36H 23/0600Z 19.6N 70.7W 50 KT 60 MPH...INLAND 48H 23/1800Z 20.5N 74.3W 55 KT 65 MPH...OVER WATER 60H 24/0600Z 22.0N 77.9W 55 KT 65 MPH 72H 24/1800Z 23.5N 81.5W 55 KT 65 MPH 96H 25/1800Z 26.3N 86.5W 65 KT 75 MPH 120H 26/1800Z 29.0N 89.0W 65 KT 75 MPH $$ FORECASTER PASCH
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