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Tropical Storm Hanna Forecast Discussion Number 9

2020-07-25 04:49:24| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT Fri Jul 24 2020 000 WTNT43 KNHC 250249 TCDAT3 Tropical Storm Hanna Discussion Number 9 NWS National Hurricane Center Miami FL AL082020 1000 PM CDT Fri Jul 24 2020 Hanna continues to strengthen over the northwestern Gulf of Mexico. Satellite and Doppler radar images indicate that the inner core continues to become better organized and the outer bands are now more symmetrical around the center. The NOAA Hurricane Hunters are currently investigating Hanna and have found maximum 850 mb flight-level winds of 72 kt and maximum SFMR winds of 51 kt. Based on this data, the initial intensity is increased to 55 kt for this advisory. The aircraft has also reported a minimum pressure of 992 mb, which is a 8 mb drop from the flight earlier today. The NOAA aircraft data indicate that the center has moved a little south of west during the past few hours, and the storm is now a little south of the previous forecast track. A strengthening subtropical ridge over the central U.S. should cause the storm to continue to move generally westward, taking the center across the southern Texas coast tomorrow afternoon or early evening. After landfall, the storm is expected to turn to the west-southwest or southwest across extreme southern Texas and northern Mexico, and that motion should continue until the system dissipates. Hanna still has another 18 hours or so to strengthen as it remains in light wind shear conditions and over the warm Gulf of Mexico waters. Since the structure of the system continues to improve, it seems likely that Hanna will reach hurricane intensity before it makes landfall. The peak intensity could be higher than what is shown in the intensity forecast below since landfall is expected to occur between the 12 and 24 h forecast times. After landfall, rapid weakening is anticipated, and Hanna is expected to dissipate on Monday over the rugged terrain of northern Mexico. The NHC intensity forecast lies at the high end of the model guidance for the next 24 h. Key Messages 1. There is a danger of life-threatening storm surge along the Texas coast from Baffin Bay 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 Saturday 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 25/0300Z 27.1N 94.8W 55 KT 65 MPH 12H 25/1200Z 27.1N 96.1W 65 KT 75 MPH 24H 26/0000Z 27.0N 97.7W 60 KT 70 MPH...INLAND 36H 26/1200Z 26.6N 99.3W 35 KT 40 MPH...INLAND 48H 27/0000Z 25.9N 101.0W 25 KT 30 MPH...INLAND 60H 27/1200Z 25.2N 102.4W 20 KT 25 MPH...POST-TROP/INLAND 72H 28/0000Z...DISSIPATED $$ Forecaster Cangialosi

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Tropical Storm Gonzalo Forecast Discussion Number 14

2020-07-25 04:40:49| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Fri Jul 24 2020 000 WTNT42 KNHC 250240 TCDAT2 Tropical Storm Gonzalo Discussion Number 14 NWS National Hurricane Center Miami FL AL072020 1100 PM AST Fri Jul 24 2020 Although there has been a recent increase in deep convection in association with Gonzalo, data from an Air Force Reserve Hurricane Hunter aircraft continues to show that the tropical cyclone is poorly organized. The aircraft has not yet found winds to support tropical storm strength, however the advisory intensity will remain a possibly generous 35-kt until the aircraft completes its mission overnight. There is also some possibility that this recent convective burst could result in some short-term re-organization. However, with the system losing organization over the past day or so, it is becoming less likely that the small cyclone will be able to significantly recover due to the nearby dry mid-level environment. The updated NHC intensity forecast no longer calls for any re-strengthening, and Gonzalo could even become a tropical depression before reaching the Windward Islands. After that time, dry air and Gonzalo's close proximity to the coast of Venezuela are likely to cause the system to weaken and degenerate into a trough of low pressure. The NHC forecast now calls for dissipation by 60 h, but this could occur sooner. Gonzalo continues moving generally westward or 270/15 kt. The system is not expected to gain much latitude as it should continue moving westward to west-northwestward within the low-level easterly flow. The track guidance continues to trend southward and the NHC track forecast has again been shifted in that direction. The new track lies to the south of the consensus aids, closest to the GFS and UKMET ensemble means. Key Messages 1. Gonzalo is forecast to bring tropical storm conditions to a portion of the southern Windward Islands Saturday and Saturday night. 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 25/0300Z 10.0N 57.1W 35 KT 40 MPH 12H 25/1200Z 10.4N 59.4W 35 KT 40 MPH 24H 26/0000Z 11.3N 62.6W 35 KT 40 MPH 36H 26/1200Z 12.2N 66.0W 30 KT 35 MPH 48H 27/0000Z 12.7N 69.7W 25 KT 30 MPH 60H 27/1200Z...DISSIPATED $$ Forecaster Brown

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Tropical Storm Hanna Forecast Discussion Number 8

2020-07-24 22:59:47| National Hurricane Center (Atlantic)

Issued at 400 PM CDT Fri Jul 24 2020 000 WTNT43 KNHC 242059 TCDAT3 Tropical Storm Hanna Discussion Number 8 NWS National Hurricane Center Miami FL AL082020 400 PM CDT Fri Jul 24 2020 Satellite imagery, along with Doppler radar data from Houston and Corpus Christi, indicate that Hanna has been getting better organized over the past several hours. Curved banding features have improved and a banding eye has developed in the radar data. The NOAA reconnaissance aircraft reported SFMR winds of 43-45 kt on its last outbound leg and a ship D5DE5 just east of the center reported an elevated wind speed of 51 kt at 1400Z. Based on these data, along with an estimated pressure of 999 mb from surrounding oil rigs, the initial intensity has been conservatively increased to 45 kt. Reconnaissance and radar fix data indicate that Hanna has turned westward, and the motion is now 275/09 kt. Hanna is forecast to move generally westward along the southern periphery of a deep-layer ridge for the next 24 hours, with landfall expected along the south-central coast of Texas within the hurricane warning area Saturday afternoon or early evening. The new NHC forecast track is just an extension of the previous advisory track, and lies close to an average of the consensus models TVCN, NOAA-HCCA, and FSSE. Given the improved internal structure noted in radar imagery, along with SSTs of at least 30 deg C and an impressive outflow pattern, increased frictional convergence as the cyclone moves closer to the coast and the approaching nocturnal convective maximum should support additional strengthening, and Hanna is now forecast to become a hurricane prior to making landfall. The NHC forecast of 65 kt in 24 hours is between the latest HWRF model run, which brings Hanna to 70 kt just prior to landfall, and the intensity consensus models HCCA and IVCN, which are just below hurricane strength. Due to Hanna forecast to reach hurricane strength, Hurricane and Storm Surge Warnings have been issued for portions of the Texas coast. Key Messages 1. There is a danger of life-threatening storm surge along the Texas coast from Baffin Bay 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 Baffin Bay to Mesquite Bay, where a Hurricane Warning is in effect. Tropical storm conditions are expected to first reach the coast within the warning area Saturday 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 24/2100Z 27.3N 94.3W 45 KT 50 MPH 12H 25/0600Z 27.4N 95.6W 55 KT 65 MPH 24H 25/1800Z 27.3N 97.2W 65 KT 75 MPH 36H 26/0600Z 27.0N 98.6W 40 KT 45 MPH...INLAND 48H 26/1800Z 26.6N 100.3W 25 KT 30 MPH...INLAND 60H 27/0600Z 25.6N 102.0W 20 KT 25 MPH...INLAND 72H 27/1800Z...DISSIPATED $$ Forecaster Stewart

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Tropical Storm Gonzalo Forecast Discussion Number 13

2020-07-24 22:37:47| National Hurricane Center (Atlantic)

Issued at 500 PM AST Fri Jul 24 2020 000 WTNT42 KNHC 242037 TCDAT2 Tropical Storm Gonzalo Discussion Number 13 NWS National Hurricane Center Miami FL AL072020 500 PM AST Fri Jul 24 2020 An Air Force Reserve Hurricane Hunter aircraft investigated Gonzalo earlier this afternoon and found it to very poorly organized. The aircraft even reported seeing multiple low-level swirls which is surprising given the small size of the cyclone. The highest flight-level winds measured by the plane were 41 kt while the highest believable SFMR values were right around 35 kt. Based on that data, Gonzalo's intensity has been lowered to 35 kt. Small systems like Gonzalo are notorious for quick changes in structure and intensity, both up and down. Therefore, despite its current downswing, it is too soon to say for sure that Gonzalo will not restrengthen to some degree before it reaches the southern Windward Islands. That said, confidence in the intensity forecast is a little higher now that we have better data to base the forecast on and it does not seem likely that Gonzalo will overcome the dry air that is currently inhibiting its development. Given the current structure of the tropical storm, the NHC intensity forecast has been lowered significantly, but still allows for some slight restrengthening during the next 24 h. The new forecast is much closer to the intensity consensus, below only the HWRF model which does not appear to have a realistic initialization. Once Gonzalo reaches the eastern Caribbean, weakening is anticipated and the cyclone is forecast to dissipate within 3 days, if not sooner. Gonzalo has sped westward all day with a motion near 270/16 kt. The guidance continues to insist that Gonzalo will gain a little latitude in the near future, and a general westward to west-northwestward motion is still forecast for the next few days. The NHC track forecast has again been shifted southward, but now lies near the middle of the guidance envelope and very near the various track consensus aids. Key Messages 1. Gonzalo is forecast to bring tropical storm conditions across portions of the southern Windward Islands Saturday and Saturday night. 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 24/2100Z 10.0N 55.6W 35 KT 40 MPH 12H 25/0600Z 10.4N 58.0W 40 KT 45 MPH 24H 25/1800Z 11.4N 61.1W 40 KT 45 MPH 36H 26/0600Z 12.2N 64.2W 40 KT 45 MPH 48H 26/1800Z 13.1N 67.9W 35 KT 40 MPH 60H 27/0600Z 13.4N 71.1W 30 KT 35 MPH 72H 27/1800Z...DISSIPATED $$ Forecaster Zelinsky

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Tropical Storm Hanna Forecast Discussion Number 7

2020-07-24 16:59:42| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Fri Jul 24 2020 000 WTNT43 KNHC 241459 TCDAT3 Tropical Storm Hanna Discussion Number 7 NWS National Hurricane Center Miami FL AL082020 1000 AM CDT Fri Jul 24 2020 Reports from a NOAA reconnaissance aircraft this morning and nearby ship D5DY4 indicate that Hanna has strengthened a little. However, the aircraft data also showed that Hanna's center had moved or reformed a little farther north near the northern edge of the convective cloud mass. A partial SSMI/S pass around 1231Z suggested that a mid-level eye feature could be forming, but it also possible that a dry slot may be intruding into the cloud shield from the northwest and west. The initial intensity of 40 kt is based on aircraft SFMR surface winds of 38-40 kt, and the 1200Z D5DY5 ship report of 48 kt at 89 meters elevation, which reduces to a 38-kt 10-meter wind speed. Even with the earlier northwestward jump in the center position, reconnaissance and microwave satellite data indicate that Hanna's motion is still west-northwestward or 285/08 kt. There remains no significant change to the previous official track forecast or reasonings over the past couple of days. The latest NHC model guidance remains in good agreement that mid-level ridge will build to the north and northwest of Hanna over the next couple of days, resulting in the cyclone turning westward by tonight and on Saturday. It should then turn west-southwestward Saturday night and Sunday. The new NHC forecast track continues to show the center making landfall along the south-central coast of Texas within the tropical storm warning area Saturday afternoon or evening, which is in good agreement with the various consensus models. Hanna's convective cloud shield remains very asymmetrical with the bulk of the convection confined to the southern semicircle despite the otherwise symmetrical and expanding upper-level outflow pattern. More recently, some deep convection has developed near the center and the aforementioned possible mid-level eye feature. Hanna is forecast to remain in relatively low vertical wind shear regime and over SSTs of 30C or more, a combination that typically favors significant intensification. However, nearby dry mid-level air noted in 1200Z soundings from Corpus Christi and Brownsville has been eroding and preventing convection from developing in the northwest quadrant and near the center, which has inhibited strengthening over the past couple of days despite the low shear conditions. The latest global model guidance shows the dry air mixing out in about 24 h just prior to landfall, which should allow for at least gradual strengthening until landfall occurs in about 30 h or so. However, if an eyewall forms during the next 12 h, then it is possible that Hanna could be near 60 kt when it makes landfall. The new NHC intensity forecast is similar to the previous advisory, and is a blend of the IVCN and HCCA consensus intensity forecasts. Key Messages 1. Hanna is forecast to strengthen and it is expected to bring tropical-storm-force winds to portions of the Texas coast, where a tropical storm warning is in effect. 2. Hanna is expected to produce heavy rains across portions of southern Texas. These rains could result in flash flooding and isolated minor to moderate river flooding. FORECAST POSITIONS AND MAX WINDS INIT 24/1500Z 27.2N 93.2W 40 KT 45 MPH 12H 25/0000Z 27.5N 94.6W 45 KT 50 MPH 24H 25/1200Z 27.4N 96.2W 55 KT 65 MPH 36H 26/0000Z 27.3N 97.6W 50 KT 60 MPH...INLAND 48H 26/1200Z 27.0N 99.0W 35 KT 40 MPH...INLAND 60H 27/0000Z 26.3N 100.4W 25 KT 30 MPH...INLAND 72H 27/1200Z 25.7N 101.6W 15 KT 15 MPH...POST-TROP/REMNT LOW 96H 28/1200Z...DISSIPATED $$ Forecaster Stewart

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