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Potential Tropical Cyclone Ten Forecast Discussion Number 1

2017-08-27 22:48:01| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Sun Aug 27 2017 000 WTNT45 KNHC 272047 TCDAT5 Potential Tropical Cyclone Ten Discussion Number 1 NWS National Hurricane Center Miami FL AL102017 500 PM EDT Sun Aug 27 2017 Convection associated with the broad area of low pressure located east of the Georgia coast has increased markedly today. Visibile satellite imagery shows multiple low-level swirls rotating around a mean center, but ASCAT data earlier today showed that the circulation was not yet well-defined. The ASCAT data and buoy observations indicate that the initial intensity is 30 kt, and buoy data suggest the central pressure is around 1007 mb. While the system is expected to remain sheared, it has a high chance of becoming a tropical depression or tropical storm before it becomes baroclinic in about 48 hours. Given that, and the potential for this system to bring tropical storm conditions to the coast from northern South Carolina through North Carolina, advisories are being initiated on this system as a Potential Tropical Cyclone. The system is currently moving little in a region of weak steering, but should begin to move slowly northward and then quickly accelerate northeastward ahead of a mid-latitude trough moving into the mid-Atlantic states. The NHC forecast follows the trend of the global models keeping the low center near the coast, but as usual there is more uncertainty than usual in the track forecast for a weak/developing system. After the system moves into the western Atlantic, it should continue accelerating east-northeastward ahead of the upper trough through the end of the period. Despite the sheared envirionment, the system should be able to intensify a little via diabatic processes before it intensifies further as it undergoes a more substantial baroclinic intensification at 48 hours and beyond. The NHC intensity forecast follows the intensity consensus through 36 hours and then follows the trend of the global model guidance and guidance from the NOAA Ocean Prediction Center. Although the potential impacts are within 36 hours, given the uncertainty in whether tropical storm force winds will occur on land in northeastern South Caroilna and southeastern North Carolina, south, a tropical storm watch has been issued for these 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 27/2100Z 31.2N 80.0W 30 KT 35 MPH...POTENTIAL TROP CYCLONE 12H 28/0600Z 31.6N 80.1W 35 KT 40 MPH...TROPICAL CYCLONE 24H 28/1800Z 32.4N 80.0W 35 KT 40 MPH 36H 29/0600Z 34.1N 78.0W 35 KT 40 MPH...INLAND 48H 29/1800Z 36.6N 75.0W 45 KT 50 MPH...POST-TROPICAL 72H 30/1800Z 40.0N 66.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 96H 31/1800Z 43.0N 55.0W 60 KT 70 MPH...POST-TROP/EXTRATROP 120H 01/1800Z 47.0N 43.0W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Brennan

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Tropical Storm Harvey Forecast Discussion Number 30

2017-08-27 22:47:06| National Hurricane Center (Atlantic)

Issued at 400 PM CDT Sun Aug 27 2017 000 WTNT44 KNHC 272046 TCDAT4 Tropical Storm Harvey Discussion Number 30 NWS National Hurricane Center Miami FL AL092017 400 PM CDT Sun Aug 27 2017 The unprecedented flooding rainfall event continues to unfold over a large area of southeastern Texas. While Harvey has been moving slowly eastward or east-southeastward today, bands of heavy rainfall have continued 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 are quite common in the Greater Houston area, and additional rainfall amounts of 15 to 25 inches are expected over the next several days. Rainfall total could reach 50 inches in some locations, which would be historic for that area. Harvey is still producing tropical-storm-force winds, with a recent observation of 34 kt with a gust to 46 kt at New Braunfels, Texas. The NHC track guidance is in better agreement showing Harvey moving just offshore of the Texas coast on Monday, then turning northward and moving inland over northeastern Texas by 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. Although a tropical storm watch has been issued, which may need to be extended eastward along the upper Texas and southwest Louisiana coast tonight, heavy rainfall and life-threatening flooding continue to 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, with isolated storm totals as high as 50 inches, through Friday. 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 FORECAST POSITIONS AND MAX WINDS INIT 27/2100Z 29.0N 97.0W 35 KT 40 MPH...INLAND 12H 28/0600Z 28.7N 96.8W 35 KT 40 MPH...INLAND 24H 28/1800Z 28.4N 96.4W 35 KT 40 MPH...NEAR THE COAST 36H 29/0600Z 28.2N 96.0W 40 KT 45 MPH...OVER WATER 48H 29/1800Z 28.4N 95.6W 40 KT 45 MPH...OVER WATER 72H 30/1800Z 29.9N 95.2W 35 KT 40 MPH...INLAND 96H 31/1800Z 31.8N 94.7W 30 KT 35 MPH...INLAND 120H 01/1800Z 33.5N 93.4W 25 KT 30 MPH...INLAND $$ Forecaster Brown

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Tropical Storm Harvey Forecast Discussion Number 29

2017-08-27 16:58:28| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Sun Aug 27 2017 000 WTNT44 KNHC 271458 TCDAT4 Tropical Storm Harvey Discussion Number 29 NWS National Hurricane Center Miami FL AL092017 1000 AM CDT Sun Aug 27 2017 Harvey continues to meander over southeastern Texas, where it is producing catastrophic and life-threatening flooding rainfall. NWS radars show that bands of deep convection continue to develop over the northwestern Gulf of Mexico and train over portions of southeastern Texas, including the Houston/Galveston metropolitan area. Rainfall amounts greater than 20-25 inches have already been reported and flash flood emergencies and warnings have been issued by local National Weather Service offices for a large portion of southeastern Texas. Additional rainfall amounts of 15 to 25 inches are expected over the next several days, and the NOAA Weather Prediction Center is now forecasting isolated storm total amounts of 50 inches. These historic rainfall amounts will exacerbate the already dire and life-threatening situation. Surface observations of winds 30-35 kt within a band of convection over the western Gulf of Mexico and along the coast of Texas support an initial intensity of 35 kt. The latest track guidance show Harvey moving slowly southeastward for the next 24 to 36 hours and the center is likely to move very close to the coast, or even offshore, between 24-48 hours. After that time, Harvey is expected to begin a northward motion which should take it inland over eastern Texas later in the period. Since a large portion of the circulation is expected to remain over water during the next several days, Harvey is maintained as a tropical storm through 72 hours. However, the strongest winds are likely to occur over the Gulf waters. Key Messages: 1. Ongoing catastrophic and life-threatening flooding will continue across southeastern Texas. Additional rainfall accumulations of 15 to 25 inches are expected, with isolated storm totals as high as 50 inches, through Friday. 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 FORECAST POSITIONS AND MAX WINDS INIT 27/1500Z 29.0N 97.4W 35 KT 40 MPH 12H 28/0000Z 28.6N 97.3W 35 KT 40 MPH...INLAND 24H 28/1200Z 28.4N 96.8W 35 KT 40 MPH...INLAND 36H 29/0000Z 28.2N 96.3W 35 KT 40 MPH...OVER WATER 48H 29/1200Z 28.2N 96.0W 35 KT 40 MPH...OVER WATER 72H 30/1200Z 29.3N 95.7W 35 KT 40 MPH...INLAND 96H 31/1200Z 30.9N 95.5W 30 KT 35 MPH...INLAND 120H 01/1200Z 32.2N 95.1W 25 KT 30 MPH...INLAND $$ Forecaster Brown

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Tropical Storm Harvey Forecast Discussion Number 28

2017-08-27 10:41:27| National Hurricane Center (Atlantic)

Issued at 400 AM CDT Sun Aug 27 2017 000 WTNT44 KNHC 270841 TCDAT4 Tropical Storm Harvey Discussion Number 28 NWS National Hurricane Center Miami FL AL092017 400 AM CDT Sun Aug 27 2017 Although the radar presentation of the inner core of Harvey has degraded considerably, the system continues to produce intense convection in bands to the east and southeast of the center. The current intensity estimate is set to 40 kt based on surface synoptic data over southeastern Texas. Since the center is expected to remain mainly over land during the forecast period, continued weakening is likely. Given that a significant portion of the circulation is over water, however, this weakening should be very slow to occur. The official intensity forecast is similar to the model consensus. Harvey has been meandering overnight and now appears to be drifting south-southwestward. The cyclone is trapped between mid-level highs to its west-northwest and east-southeast. Over the next couple of days, the flow on the southern periphery of a trough dropping over the east-central United States should cause Harvey to move slowly southeastward to eastward. Later in the forecast period, increased ridging to east of the cyclone should cause Harvey to turn northward. The official track forecast is close to the latest model consensus and brings the center to the coast and, briefly, just offshore of southeastern Texas. At this time, it is not expected that Harvey will move far enough out over the water to result in regeneration. The biggest concern with Harvey is now the rain, a lot of rain. Rainfall totals of nearly 20 inches have been reported in the Houston area. This is resulting in catastrophic flooding which, unfortunately, will continue for some time. Key Messages: 1. While Harvey's winds are decreasing, life-threatening hazards will continue from heavy rainfall over much of southeastern Texas and from storm surge along portions of the Texas coast. 2. Catastrophic and life-threatening flooding is expected across the middle and upper Texas coast from additional rainfall of 15 to 25 inches, with isolated storm totals as high as 40 inches, through Thursday. Please heed the advice of local officials 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 3. A Storm Surge Warning remains in effect for portions of the Texas coast. Life-threatening storm surge flooding will be slow to recede due to the slow motion of Harvey and a prolonged period of onshore flow. For a depiction of areas at risk, see the Storm Surge Watch/Warning Graphic at hurricanes.gov. FORECAST POSITIONS AND MAX WINDS INIT 27/0900Z 29.2N 97.7W 40 KT 45 MPH 12H 27/1800Z 29.0N 97.4W 35 KT 40 MPH...INLAND 24H 28/0600Z 28.7N 97.0W 30 KT 35 MPH...INLAND 36H 28/1800Z 28.5N 96.6W 30 KT 35 MPH...NEAR THE COAST 48H 29/0600Z 28.5N 96.1W 30 KT 35 MPH...INLAND 72H 30/0600Z 29.4N 95.6W 30 KT 35 MPH...INLAND 96H 31/0600Z 30.8N 95.5W 25 KT 30 MPH...INLAND 120H 01/0600Z 32.0N 95.0W 25 KT 30 MPH...INLAND $$ Forecaster Pasch

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Tropical Storm Harvey Forecast Discussion Number 27

2017-08-27 04:47:26| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT Sat Aug 26 2017 000 WTNT44 KNHC 270247 TCDAT4 Tropical Storm Harvey Discussion Number 27 NWS National Hurricane Center Miami FL AL092017 1000 PM CDT Sat Aug 26 2017 The central convection associated with Harvey has shown warming cloud tops during the past several hours, although radar data shows widespread rain continuing near and north of the center. Winds from the New Braunfels WSR-88D are near 65 kt at 1500-2500 ft near the center, but it is uncertain how well these winds are mixing down to the surface. The initial intensity is reduced to a somewhat uncertain 45 kt based mainly on the radar data. Harvey has drifted east-northeastward since the last advisory. While the model guidance is not in great agreement, it appears that the cyclone will drift southward or southeastward during the next couple of days due to the distant influence of a trough digging into the eastern United States. After that time, a building ridge over the Gulf of Mexico should cause Harvey to drift generally northward. The new forecast track is similar to the previous track and lies near the consensus models. At this time, the forecast track keeps the center of Harvey inland, as there is not enough agreement between the models that the center of Harvey will actually emerge over water. Harvey should continue to weaken to a tropical depression during the next day or so as the cyclone remains inland. As the center nears the coast, it is likely that the cyclone will maintain that status for several days as a large amount of the circulation will be over the water. By the end of the forecast period, the system should be far enough inland so that Harvey will again weaken. An alternative scenario is that Harvey could re-intensify if the center emerges over the Gulf. Key Messages: 1. While Harvey's winds are decreasing, life-threatening hazards will continue from heavy rainfall over much of southeastern Texas and from storm surge along portions of the Texas coast. 2. Catastrophic and life-threatening flooding is expected across the middle and upper Texas coast from additional rainfall of 15 to 25 inches, with isolated storm totals as high as 40 inches, through Thursday. Please heed the advice of local officials 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 3. A Storm Surge Warning remains in effect for portions of the Texas coast. Life-threatening storm surge flooding will be slow to recede due to the slow motion of Harvey and a prolonged period of onshore flow. For a depiction of areas at risk, see the Storm Surge Watch/Warning Graphic at hurricanes.gov. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 29.3N 97.3W 45 KT 50 MPH...INLAND 12H 27/1200Z 29.1N 97.4W 35 KT 40 MPH...INLAND 24H 28/0000Z 28.9N 97.3W 30 KT 35 MPH...INLAND 36H 28/1200Z 28.5N 97.0W 30 KT 35 MPH...INLAND 48H 29/0000Z 28.4N 96.8W 30 KT 35 MPH...INLAND 72H 30/0000Z 29.0N 96.5W 30 KT 35 MPH...INLAND 96H 31/0000Z 30.0N 96.5W 30 KT 35 MPH...INLAND 120H 01/0000Z 31.0N 96.5W 25 KT 30 MPH...INLAND $$ Forecaster Beven

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