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Tropical Storm Harvey Forecast Discussion Number 33

2017-08-28 16:50:05| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Mon Aug 28 2017 000 WTNT44 KNHC 281449 TCDAT4 Tropical Storm Harvey Discussion Number 33 NWS National Hurricane Center Miami FL AL092017 1000 AM CDT Mon Aug 28 2017 Radar and surface data indicate that the center of Harvey is near or just off the Texas coast south of Matagorda. The system currently has only disorganized convection near the center, with the primary deep convection in a band well to the east of the center. The initial intensity remains 35 kt based on a minimum central pressure around 997 mb and the assumption that stronger winds aloft seen on the Houston WSR-88D are mixing down to the surface in the stronger bands. While the convection is currently poorly organized, very heavy rains and life-threatening flash flooding continue over southeastern Texas and southwestern Louisiana. There have been reports of 2-day rainfall totals of close to 30 inches in the Greater Houston area. With the additional rains that are expected over the next several days, rainfall totals could reach 50 inches in some locations, which would be historic for the area. Due to the current structure, a dry slot seen in water vapor imagery over the southern part of the circulation, and the lack of intensification shown by the intensity guidance, only slight strengthening is anticipated while Harvey remains over the Gulf of Mexico. The new intensity forecast is an update of the previous one. Radar and surface observations indicate that the center is moving slowly southeastward, or 125/4 kt. A mid-level trough dropping into the Ohio Valley should cause Harvey to turn toward the east and northeast and move back over land in a couple of days. There is little change to the forecast track from the previous advisory, and the new track remains close to the dynamical model consensus. Key Messages: 1. Ongoing catastrophic and life-threatening flooding will continue across southeastern Texas. Additional rainfall accumulations of 15 to 25 inches are expected across the upper Texas coast, with isolated storm totals as high as 50 inches. Please heed the advice of local officials. Do not attempt to travel if you are in a safe place, and do not drive into flooded roadways. Refer to products from your local National Weather Service office and the NOAA Weather Prediction Center for more information on the flooding hazard. A summary of rainfall totals compiled by the Weather Prediction Center can be found at: www.wpc.ncep.noaa.gov/discussions/nfdscc1.html 2. The flood threat is spreading farther east into Louisiana. Additional rainfall amounts of 15 to 25 inches are expected in southwestern Louisiana, with rainfall amounts of 5 to 15 inches expected in south-central Louisiana and 5 to 10 inches in southeastern Louisiana. Please heed the advice of local officials and refer to products from your local National Weather Service office and the NOAA Weather Prediction Center for more information on the flooding hazard in these areas. 3. While Tropical Storm Watches and Warnings have been extended eastward to the coast of Louisiana, the impacts of winds and storm surge are expected to be secondary compared to that of the rains. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 28.5N 96.0W 35 KT 40 MPH 12H 29/0000Z 28.1N 95.7W 35 KT 40 MPH 24H 29/1200Z 28.1N 95.3W 35 KT 40 MPH 36H 30/0000Z 28.5N 94.8W 40 KT 45 MPH 48H 30/1200Z 29.4N 94.4W 40 KT 45 MPH 72H 31/1200Z 31.5N 93.5W 35 KT 40 MPH...INLAND 96H 01/1200Z 33.5N 92.0W 30 KT 35 MPH...INLAND 120H 02/1200Z 35.5N 90.5W 20 KT 25 MPH...INLAND $$ Forecaster Beven

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Potential Tropical Cyclone Ten Forecast Discussion Number 3

2017-08-28 10:57:04| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Mon Aug 28 2017 000 WTNT45 KNHC 280856 TCDAT5 Potential Tropical Cyclone Ten Discussion Number 3 NWS National Hurricane Center Miami FL AL102017 500 AM EDT Mon Aug 28 2017 Potential Tropical Cyclone Ten continues to lack a well-defined center, as shown in the coastal stations, buoys, and ASCAT scatterometer passes. Moreover, the convection - while deep - is now strung out linearly from northeast to southwest, more reminiscent of a front or trough. Thus it does not appear that genesis into a tropical cyclone is imminent. Observations from buoys and the ASCAT passes indicate that the peak winds remain about 30 kt. While the disturbance has plenty of warm water and moist air available, it's being sheared by strong upper-level westerlies. The shear may lessen slightly over the next day or so, allowing a short window of opportunity for the system to undergo genesis and some intensification. But in about 36-48 hr, the shear should go back up as the system reaches cooler SSTs, likely limiting the intensification as a tropical cyclone. At about the same time, the system should transform into an extratropical cyclone and further develop via baroclinic forcing. The intensity forecast shows a slightly delayed genesis and more gradual intensification through 24 hr compared to the previous advisory and about the same thereafter. This forecast is based upon a blend of the statistical, hurricane-mesoscale, and global models. The disturbance is officially shown as stationary, but this is an educated guess without a well-defined center being present. After meandering for another 12 hr or so, the system should consolidate and begin accelerating off toward the northeast. The mesoscale and global guidance shows higher uncertainty than usual in the 12-36 hr time frame and lower uncertainty for the 72 hr and beyond forecasts, likely because of the variability in the models of where and when a well-defined center forms. The official track forecast is very similar to the previous one. The track, intensity, and size forecasts for 48 hr and beyond are based upon guidance provided by the Ocean Prediction Center. Note that even though potential impacts from this system's winds could occur within the 36 hr time frame for a Tropical Storm Warning, because the intensity forecast is for a low-end tropical storm and the winds are all over the eastern semicircle, the threat of coastal tropical storm winds remains possible but low. Thus the Tropical Storm Watch for portions of South Carolina and North Carolina are retained at this time. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 30.3N 81.0W 30 KT 35 MPH...POTENTIAL TROP CYCLONE 12H 28/1800Z 31.1N 80.9W 30 KT 35 MPH 24H 29/0600Z 32.9N 79.2W 35 KT 40 MPH...TROPICAL CYCLONE 36H 29/1800Z 35.0N 76.1W 40 KT 45 MPH...INLAND 48H 30/0600Z 37.5N 72.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 31/0600Z 41.0N 62.0W 60 KT 70 MPH...POST-TROP/EXTRATROP 96H 01/0600Z 44.0N 51.5W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 02/0600Z 48.5N 37.0W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Landsea

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Tropical Storm Harvey Forecast Discussion Number 32

2017-08-28 10:57:01| National Hurricane Center (Atlantic)

Issued at 400 AM CDT Mon Aug 28 2017 000 WTNT44 KNHC 280856 TCDAT4 Tropical Storm Harvey Discussion Number 32 NWS National Hurricane Center Miami FL AL092017 400 AM CDT Mon Aug 28 2017 Harvey is producing intense convection in bands over the eastern semicircle of the circulation. This is resulting in the continuation of very heavy rains and life-threatening flash flooding over southeastern Texas and southwestern Louisiana. There have been reports of 2-day rainfall totals of close to 30 inches in the Greater Houston area. With the additional rains that are expected over the next several days, rainfall totals could reach 50 inches in some locations, which would be historic for the area. The initial intensity estimate remains 35 kt, based on the assumption that winds of this strength are occuring in some of the stronger bands. Since Harvey is forecast to be back over water just offshore of the coast during the next couple of days, there is some potential for restrengthening. Significant strengthening is not anticipated, however, due to the system's lack of an inner core and strong southwesterly shear associated with an upper-level trough over Texas. Radar and surface observations indicate that the center is moving slowly southeastward, or 130/3 kt. A mid-level trough dropping into the Ohio Valley should cause Harvey to turn toward the east and northeast and move back over land in a couple of days. The official track forecast remains close to the dynamical model consensus. Although the tropical storm warning may need to be extended eastward along the upper Texas and southwest Louisiana coasts later this morning, heavy rainfall and life-threatening flooding continue to be the primary threats. Key Messages: 1. Ongoing catastrophic and life-threatening flooding will continue across southeastern Texas. Additional rainfall accumulations of 15 to 25 inches are expected across the upper Texas coast, with isolated storm totals as high as 50 inches. Please heed the advice of local officials. Do not attempt to travel if you are in a safe place, and do not drive into flooded roadways. Refer to products from your local National Weather Service office and the NOAA Weather Prediction Center for more information on the flooding hazard. A summary of rainfall totals compiled by the Weather Prediction Center can be found at: www.wpc.ncep.noaa.gov/discussions/nfdscc1.html 2. The flood threat is spreading farther east into Louisiana. Additional rainfall amounts of 15 to 25 inches are expected in southwestern Louisiana, with rainfall amounts of 5 to 15 inches expected in south-central Louisiana. Please heed the advice of local officials and refer to products from your local National Weather Service office and the NOAA Weather Prediction Center for more information on the flooding hazard in these areas. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 28.6N 96.3W 35 KT 40 MPH 12H 28/1800Z 28.4N 96.0W 35 KT 40 MPH...OVER WATER 24H 29/0600Z 28.1N 95.6W 35 KT 40 MPH...OVER WATER 36H 29/1800Z 28.3N 95.2W 40 KT 45 MPH...OVER WATER 48H 30/0600Z 29.0N 94.7W 40 KT 45 MPH...OVER WATER 72H 31/0600Z 31.0N 93.9W 35 KT 40 MPH...INLAND 96H 01/0600Z 33.4N 92.5W 30 KT 35 MPH...INLAND 120H 02/0600Z 35.0N 90.5W 25 KT 30 MPH...INLAND $$ Forecaster Pasch

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Tropical Storm Harvey Forecast Discussion Number 31

2017-08-28 04:35:05| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT Sun Aug 27 2017 000 WTNT44 KNHC 280234 TCDAT4 Tropical Storm Harvey Discussion Number 31 NWS National Hurricane Center Miami FL AL092017 1000 PM CDT Sun Aug 27 2017 The unprecedented flooding rainfall event continues to unfold over much of southeastern Texas. Harvey has been moving slowly east- southeastward during the past few hours, and heavy rainbands continue to form over the northwestern Gulf and train inland over much of the upper Texas coast and southwestern Louisiana. Storm total rainfall amounts in the 20-27 inch range have been observed across much of the Greater Houston area, and additional rainfall amounts of 15 to 25 inches are expected over the next several days. Rainfall totals could reach 50 inches in some locations, which would be historic for that area. There haven't been any observations of sustained 34-kt winds over land for the past few hours, but the initial intensity remains 35 kt based on the assumption that higher winds are occuring over water, likely in rainbands. The track guidance continues to show Harvey moving just offshore of the Texas coast on Monday, then turning northward and moving inland over northeastern Texas in 48 to 72 hours. All of the global models show some slight deepening of the system after it moves over water, but given the lack of an inner core, significant strengthening is not anticipated. The new NHC track and intensity forecasts are similar to those from the previous advisory. Although the tropical storm warning has been expanded, and may need to be extended eastward along the upper Texas and southwest Louisiana coasts tomorrow morning, heavy rainfall and life- threatening flooding continue to be the primary threats. Key Messages: 1. Ongoing catastrophic and life-threatening flooding will continue across southeastern Texas. Additional rainfall accumulations of 15 to 25 inches are expected across the upper Texas coast, with isolated storm totals as high as 50 inches. Please heed the advice of local officials. Do not attempt to travel if you are in a safe place, and do not drive into flooded roadways. Refer to products from your local National Weather Service office and the NOAA Weather Prediction Center for more information on the flooding hazard. A summary of rainfall totals compiled by the Weather Prediction Center can be found at: www.wpc.ncep.noaa.gov/discussions/nfdscc1.html 2. The flood threat is spreading farther east into Louisiana. Additional rainfall amounts of 15 to 25 inches are expected in southwestern Louisiana, with rainfall amounts of 5 to 15 inches expected in south-central Louisiana. Please heed the advice of local officials and refer to products from your local National Weather Service office and the NOAA Weather Prediction Center for more information on the flooding hazard in these areas. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 28.8N 96.6W 35 KT 40 MPH...INLAND 12H 28/1200Z 28.6N 96.4W 35 KT 40 MPH...NEAR THE COAST 24H 29/0000Z 28.3N 96.0W 40 KT 45 MPH...OVER WATER 36H 29/1200Z 28.4N 95.7W 40 KT 45 MPH...OVER WATER 48H 30/0000Z 28.8N 95.3W 40 KT 45 MPH...OVER WATER 72H 31/0000Z 30.5N 94.8W 35 KT 40 MPH...INLAND 96H 01/0000Z 32.3N 93.9W 30 KT 35 MPH...INLAND 120H 02/0000Z 34.0N 92.5W 25 KT 30 MPH...INLAND $$ Forecaster Brennan

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Potential Tropical Cyclone Ten Forecast Discussion Number 2

2017-08-28 04:34:33| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Sun Aug 27 2017 000 WTNT45 KNHC 280234 TCDAT5 Potential Tropical Cyclone Ten Discussion Number 2 NWS National Hurricane Center Miami FL AL102017 1100 PM EDT Sun Aug 27 2017 Deep convection has been increasing in both intensity and coverage during the past several hours in association with Potential Tropical Cyclone Ten. However, satellite and radar data indicate that the circulation remains poorly defined, therefore, the system is not yet a tropical cyclone. The initial intensity is held at 30 kt based on the surrounding surface observations and the earlier ASCAT data. The disturbance is located in weak steering currents, and has been meandering during the last several hours. A continued slow and erratic motion is likely to continue overnight and early Monday. A mid- to upper-level trough currently over the central U.S. is expected to approach the system, and should cause the disturbance to begin moving northeastward by late Monday. A faster east- northeastward to northeastward motion is forecast thereafter when the system becomes embedded in the mid-latitude westerlies. The models are in fair agreement, and only small changes were made to the previous NHC track forecast. This forecast takes the center of the disturbance near the Georgia and South Carolina coasts tonight and Monday and along the North Carolina coastline Monday night and Tuesday. The elongated center of the disturbance is located to the west of the main area of deep convection due to strong westerly vertical wind shear. The shear is only expected to lessen a little during the next 12 to 24 hours, but it will likely weaken enough to allow the system to become a tropical cyclone. After that time, increasing shear and interaction with the aforementioned trough should cause the disturbance to lose its tropical characteristics in about 48 hours. Strengthening is likely for a couple of days while the system is post-tropical due to baroclinic effects. Although the potential for tropical storm winds are within the warning time period (36 hours), given the uncertainty in whether these winds will occur on land in northeastern South Carolina and southeastern North Carolina, a tropical storm watch remains in effect for those areas. Note that north of Duck, North Carolina, hazards from this system will be handled with non-tropical products issued by local National Weather Service offices. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 30.5N 80.8W 30 KT 35 MPH...POTENTIAL TROP CYCLONE 12H 28/1200Z 30.9N 81.0W 35 KT 40 MPH...TROPICAL CYCLONE 24H 29/0000Z 32.3N 79.9W 35 KT 40 MPH 36H 29/1200Z 34.4N 77.5W 35 KT 40 MPH...NEAR THE COAST 48H 30/0000Z 36.5N 73.8W 45 KT 50 MPH...POST-TROPICAL 72H 31/0000Z 39.9N 64.2W 55 KT 65 MPH...POST-TROP/EXTRATROP 96H 01/0000Z 43.2N 53.4W 60 KT 70 MPH...POST-TROP/EXTRATROP 120H 02/0000Z 47.2N 41.1W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Cangialosi

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