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Tropical Storm Hanna Forecast Discussion Number 15
2020-07-26 16:45:44| National Hurricane Center (Atlantic)
Issued at 1000 AM CDT Sun Jul 26 2020 058 WTNT43 KNHC 261445 TCDAT3 Tropical Storm Hanna Discussion Number 15 NWS National Hurricane Center Miami FL AL082020 1000 AM CDT Sun Jul 26 2020 Surface observations and WSR-88D radar data from Brownsville, Texas, indicate that Hanna continues to weaken as it moves farther inland. The radar shows a couple of fairly well-defined bands of convection over the eastern semicircle and tropical-storm-force wind gusts have been reported at observing sites along the U.S./Mexico border within the past couple of hours. The initial intensity has been reduced to 40 kt, and is based primarily on recent observations and Doppler radar velocities. Hanna should continue to weaken quickly during the next 12-24 hours as it moves inland over Mexico. Hanna is forecast to become a tropical depression later today and dissipate over the mountainous terrain of Mexico by Monday night. Hanna is moving west-southwestward or 250/8 kt. The system is forecast to continue moving west-southwestward around the southern portion of a mid-level ridge over the central United States. The new NHC track forecast is similar to the previous advisory and lies near the various consensus aids. Key Messages 1. Tropical storm conditions are expected to persist into this afternoon near and to the east of the center of Hanna. 2. Heavy rainfall from Hanna has already produced numerous reports of flash flooding across south Texas. Additional heavy rainfall will continue to cause life-threatening flash flooding over south Texas and northern Mexico, and isolated minor to moderate river flooding in south Texas. 3. Storm surge along the Texas coast should continue to diminish today. FORECAST POSITIONS AND MAX WINDS INIT 26/1500Z 26.1N 99.7W 40 KT 45 MPH 12H 27/0000Z 25.5N 100.6W 30 KT 35 MPH...INLAND 24H 27/1200Z 25.0N 101.9W 25 KT 30 MPH...INLAND 36H 28/0000Z 24.9N 102.9W 20 KT 25 MPH...POST-TROP/INLAND 48H 28/1200Z...DISSIPATED $$ Forecaster Brown
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Tropical Storm Hanna Forecast Discussion Number 14
2020-07-26 10:53:42| National Hurricane Center (Atlantic)
Issued at 400 AM CDT Sun Jul 26 2020 000 WTNT43 KNHC 260853 TCDAT3 Tropical Storm Hanna Discussion Number 14 NWS National Hurricane Center Miami FL AL082020 400 AM CDT Sun Jul 26 2020 Hanna continues to weaken as the center crosses the Rio Grande River from Texas into northeastern Mexico. Satellite imagery shows some warming of the cloud tops near the center, and WSR-88D radar data shows that only about a third of the previous eyewall is still present to the southeast of the center. The storm is generating a vigorous outer convective band over the eastern semicircle. The initial intensity is reduced to 50 kt based mainly on Doppler radar winds of 50-65 kt at about 9000 ft to the northeast of the center, and it is possible that this is generous. The initial motion remains west-southwestward or 250/8 kt. The mid-level ridge over the central United States should continue to steer Hanna west-southwestward until dissipation, and the new NHC forecast track is little changed from the previous forecast. Hanna should rapidly weaken as it moves over northeastern Mexico, with the system expected to weaken to a depression in 12-18 h, if not sooner. The system is expected to dissipate completely over the rugged terrain of Mexico between 36-48 h. The radar signature of the storm has weakened to the point where there will be no more hourly position updates between advisories. Key Messages 1. Tropical storm conditions are expected to persist for several more hours near the center of Hanna, and for a few more hours in the warning area along the coast of Texas and northeastern Mexico. 2. Hanna is expected to produce heavy rains across portions of southern Texas and northeastern Mexico. These rains will result in life-threatening flash flooding and isolated minor to moderate river flooding. 3. Storm surge along the Texas coast should diminish today. FORECAST POSITIONS AND MAX WINDS INIT 26/0900Z 26.3N 98.9W 50 KT 60 MPH...INLAND 12H 26/1800Z 25.8N 99.9W 35 KT 40 MPH...INLAND 24H 27/0600Z 25.1N 101.4W 25 KT 30 MPH...INLAND 36H 27/1800Z 24.5N 102.7W 20 KT 25 MPH...POST-TROP/INLAND 48H 28/0600Z...DISSIPATED $$ Forecaster Beven
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Hurricane Hanna Forecast Discussion Number 12
2020-07-25 22:59:37| National Hurricane Center (Atlantic)
Issued at 400 PM CDT Sat Jul 25 2020 000 WTNT43 KNHC 252059 TCDAT3 Hurricane Hanna Discussion Number 12 NWS National Hurricane Center Miami FL AL082020 400 PM CDT Sat Jul 25 2020 NOAA Doppler weather radar data from Brownsville and Corpus Christi, Texas, along with reconnaissance data from the Air Force Hurricane Hunters indicate that Hanna has continued to strengthen this afternoon. A 30-nmi-wide eye remains distinct in the radar data, and dropsonde and 700-mb flight-level-level height data from the aircraft indicate that the central pressure has decreased to 973 mb. The aircraft measured a peak 700-mb flight-level wind speed of 86 kt on its last outbound leg, which equates to about 77 kt at the surface. Coincident with the flight-level wind data were SFMR surface wind speeds of 80 kt. In addition, Doppler velocity values have been averaging close to 100 kt between 5000-6000 ft in the northern and northeastern eyewall, which converts to 80-kt surface wind speed estimates. Based on these data, the initial intensity has been increased to 80 kt. No further strengthening is anticipated before the center of Hanna's eye makes landfall along the south Texas coast in a few hours. Doppler radar and aircraft reconnaissance fixes indicate that Hanna has finally made the much anticipated turn toward the west-southwest, now showing an initial motion of 255/07 kt. A west-southwestward motion is expected to continue for the next 48 hours, which will take Hanna well inland over south Texas, followed by eventual dissipation in about 48 h over over the mountains of northeastern Mexico. The new NHC track forecast remains unchanged from the previous advisory, and lies near the center of the tightly packed consensus models. Key Messages 1. Life-threatening storm surge will continue along portions of the Texas coast from Port Mansfield to Sargent, where a Storm Surge Warning is in effect. Residents in these locations should follow advice given by local emergency officials. 2. Hurricane conditions will continue within the Hurricane Warning area along the Texas coast through this evening. Strong winds will also spread inland across portions of South Texas where Tropical Storm and Hurricane Warnings are in effect. 3. Hanna is expected to produce heavy rains across portions of southern Texas and northeastern Mexico. These rains will result in life-threatening flash flooding and isolated minor to moderate river flooding. FORECAST POSITIONS AND MAX WINDS INIT 25/2100Z 26.8N 97.2W 80 KT 90 MPH 12H 26/0600Z 26.7N 98.4W 50 KT 60 MPH...INLAND 24H 26/1800Z 26.0N 100.0W 30 KT 35 MPH...INLAND 36H 27/0600Z 25.5N 101.4W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 27/1800Z...DISSIPATED INLAND $$ Forecaster Stewart
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Hurricane Hanna Forecast Discussion Number 11
2020-07-25 16:58:29| National Hurricane Center (Atlantic)
Issued at 1000 AM CDT Sat Jul 25 2020 000 WTNT43 KNHC 251458 TCDAT3 Hurricane Hanna Discussion Number 11 NWS National Hurricane Center Miami FL AL082020 1000 AM CDT Sat Jul 25 2020 NOAA Doppler radar data from Corpus Christi and Brownsville, Texas, along with reconnaissance data from the NOAA Hurricane Hunters indicate that Hanna has continued to strengthen this morning. A well-defined but fairly large 30-35-nmi-wide eye has formed and recent dropsonde data from the eye indicate that the central pressure has dropped to 978 mb. The aircraft measured a peak 700-mb flight-level wind speed of 77 kt, which equates to about 69 kt at the surface. During the past hour, Doppler velocities have sharply increased with numerous patches of 85-90 kt between 7000-8000 ft common in the northern eyewall. Although these values would typically correspond to surface winds of about 75 kt, the Doppler velocity are occurring in low reflectivity regions of 25-30 dBZ, so the full effect of those winds are likely not reaching the surface. This could be why the highest SFMR surface wind observed by the aircraft was only 63 kt. The initial intensity has been increased to 70 kt, which is a blend of the aircraft flight-level, radar, and SFMR surface wind speed estimates. The center position is a tad north of the recon fixes due to some southward tilt of the eye caused by northerly shear. This has resulted in a slower westward motion of 270/06 kt. The ridge to the north of the hurricane has been slowly building westward and southwestward based on upper-air data over the past 24 hours. This slow ridging pattern is expected to continue for the next 48 hours, resulting in Hanna gradually turning toward the west-southwest by late this afternoon or evening, with landfall occurring in about 12 h along south Texas coast. After landfall, Hanna should continue its west-southwestward motion until dissipation over the mountainous terrain of northeastern Mexico in 48-60 h. The new NHC track forecast is similar to the previous advisory track, and lies close to the tightly packed consensus model guidance. Although the deep-layer vertical wind shear is expected to remain out of the north-northwest to north at about 20 kt, the relatively large and stable eye, along with the expected convective vigor of the hurricane, could result in a little more strengthening just before landfall occurs. After landfall, rapid weakening of the wind field is expected. However, the weakening peak winds will have no negative effect on the likelihood for heavy rainfall or the possibility of isolated tornadoes developing. Key Messages 1. Life-threatening storm surge is occurring along portions of the Texas coast from Port Mansfield to Sargent, where a Storm Surge Warning is in effect. Residents in these locations should follow advice given by local emergency officials. 2. Hurricane conditions are expected along the Texas coast from Port Mansfield to Mesquite Bay, where a Hurricane Warning is in effect. Tropical storm conditions are expected to first reach the coast within the warning area this morning. 3. Hanna is expected to produce heavy rains across portions of southern Texas and northeastern Mexico. These rains could result in life-threatening flash flooding and isolated minor to moderate river flooding. FORECAST POSITIONS AND MAX WINDS INIT 25/1500Z 27.1N 96.3W 70 KT 80 MPH 12H 26/0000Z 26.9N 97.6W 70 KT 80 MPH...INLAND 24H 26/1200Z 26.4N 99.1W 45 KT 50 MPH...INLAND 36H 27/0000Z 25.9N 100.6W 25 KT 30 MPH...INLAND 48H 27/1200Z 25.3N 102.1W 15 KT 15 MPH...POST-TROP/REMNT LOW 60H 28/0000Z...DISSIPATED $$ Forecaster Stewart
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Tropical Storm Gonzalo Forecast Discussion Number 15
2020-07-25 10:43:24| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sat Jul 25 2020 000 WTNT42 KNHC 250843 TCDAT2 Tropical Storm Gonzalo Discussion Number 15 NWS National Hurricane Center Miami FL AL072020 500 AM AST Sat Jul 25 2020 On the last leg in the east semicircle of Gonzalo, the 53rd Air Force Reserve Hurricane Hunter aircraft reported numerous SFMR winds of 35 to 40 kts, with lighter winds at flight-level. The surface circulation, however, was still poorly defined, and barely closed. Based on the reconnaissance observations, the initial intensity is held at 35 kt for this advisory. Due to the fact that Gonzalo is moving within an impeding thermodynamic environment, little change in intensity is forecast as the cyclone approaches the southern Windward Islands this afternoon. As Gonzalo moves into the eastern Caribbean Sea, lingering large-scale subsidence and the cyclone's close proximity to the coast of Venezuela are predicted to cause the system to weaken and degenerate into a trough of low pressure in a couple of days which is consistent with the global model's solution. The initial motion is estimated to be westward, or 270/15 kt. Gonzalo should gain very little latitude with time as it continues moving westward to west-northwestward within the fresh low-level tradewind flow. The official forecast is once again nudged a bit toward the south and aligns with the NOAA HFIP HCCA consensus model. Key Messages 1. Gonzalo is forecast to bring tropical storm conditions to a portion of the southern Windward Islands today and tonight. Tropical Storm Warnings are currently in effect for some of the islands. Interests in the southern Windward Islands should monitor the progress of Gonzalo and follow any advice given by local officials. 2. Gonzalo is expected to produce heavy rain over portions of the southern Windward Islands. This could lead to life-threatening flash flooding. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 10.1N 58.7W 35 KT 40 MPH 12H 25/1800Z 10.7N 61.4W 35 KT 40 MPH 24H 26/0600Z 11.5N 65.3W 30 KT 35 MPH 36H 26/1800Z 12.1N 69.4W 30 KT 35 MPH 48H 27/0600Z...DISSIPATED $$ Forecaster Roberts
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