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Post-Tropical Cyclone Olga Forecast Discussion Number 3

2019-10-26 04:53:39| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT Fri Oct 25 2019 000 WTNT42 KNHC 260253 TCDAT2 Post-Tropical Cyclone Olga Discussion Number 3 NWS National Hurricane Center Miami FL AL172019 1000 PM CDT Fri Oct 25 2019 Earlier this evening, the last 2 passes through Olga made by an Air Force Reserve Hurricane Hunter aircraft showed that the cyclone becoming embedded within a cold front. Strong northwesterly flow was observed within 10 n mi northwest of Olga's center and a sharp temperature and dew point gradient was measured across the cyclone. It does not appear that Olga has separated from the front in any significant way since the plane left. In fact, recent surface observations suggest that either the front passes through the center of the cyclone or its circulation has become poorly defined. Based on all these data, Olga is now classified as post-tropical and this is the last NHC advisory. Since Olga is entangled with the front, the winds and seas associated the front are now considered to be representative of the overall system. The intensity of the post-tropical cyclone is set at 45 kt based on SFMR winds of 48 kt and flight-level winds of 54 kt found by the plane behind the front. No substantial change in Olga's strength is anticipated before it reaches the coast Saturday morning, and the winds should decrease quickly thereafter. The post-tropical cyclone is forecast to move quickly up the Mississippi Valley on Saturday, before turning northeastward toward the Great Lakes late Saturday or early Sunday. Dissipation is anticipated before the end of the weekend. Severe weather, including heavy rain, gusty winds, and isolated tornadoes will be the primary hazard associated with post-tropical Olga as it races northward. Coastal flooding is also possible tonight along portions of the Louisiana coast. For more information specific to your area, please see products from your local weather service office at weather.gov. Key messages: 1. Olga is now a post-tropical cyclone. Detailed information about hazards related to wind, rainfall, coastal flooding, and tornadoes can be found in products issued by local National Weather Service forecast offices, available at weather.gov FORECAST POSITIONS AND MAX WINDS INIT 26/0300Z 27.8N 92.2W 45 KT 50 MPH...POST-TROPICAL 12H 26/1200Z 31.8N 90.4W 35 KT 40 MPH...POST-TROP/EXTRATROP 24H 27/0000Z 38.0N 88.5W 30 KT 35 MPH...POST-TROP/EXTRATROP 36H 27/1200Z 43.5N 83.5W 30 KT 35 MPH...POST-TROP/EXTRATROP 48H 28/0000Z...DISSIPATED $$ Forecaster Zelinsky

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Tropical Storm Pablo Forecast Discussion Number 2

2019-10-26 04:40:16| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Fri Oct 25 2019 000 WTNT43 KNHC 260240 TCDAT3 Tropical Storm Pablo Discussion Number 2 NWS National Hurricane Center Miami FL AL182019 1100 PM AST Fri Oct 25 2019 Pablo continues to exhibit a tight circulation with an occasional eye feature evident in satellite images, which is why the system is classified a tropical storm. However, a larger look at the east Atlantic reveals that Pablo is a tiny feature within a broad extratropical cyclone. The initial wind speed is held at 40 kt, which is based on a recent ASCAT-C overpass that showed a small area of tropical-storm-force winds near the center. It should be noted that a much larger area of winds of about the same strength, associated with the parent extratropical low, exist to the north and west of Pablo. The small tropical storm is moving east-southeastward at 8 kt as the overall trough continues to dig in that direction. A turn to the east should occur by early Saturday, followed by a faster northeastward or north-northeastward motion by Saturday night, taking the cyclone across the Azores. By the end of the weekend and early next week, a slower northward motion seems likely before the storm is absorbed by another extratropical low to its west. The NHC track forecast lies near the middle of the guidance envelope. Pablo could strengthen a little during the next 24 hours while it remains in unstable conditions and over waters that should support some convection. However, the system is expected to move over sharply colder waters Saturday night and Sunday, and that should cause Pablo to lose its tropical characteristics. The models show the extratropical low dissipating or becoming absorbed by another extratropical low in a little more than 3 days. Given that Pablo is embedded within a large extratropical low, which itself is forecast to bring strong winds to the Azores, the Portuguese Institute for the Sea and Atmosphere (IPMA) has included the effects of this small cyclone in their products. Those products already account for the strong winds and high waves expected in the Azores. FORECAST POSITIONS AND MAX WINDS INIT 26/0300Z 35.5N 31.1W 40 KT 45 MPH 12H 26/1200Z 35.6N 28.9W 45 KT 50 MPH 24H 27/0000Z 37.7N 25.1W 45 KT 50 MPH 36H 27/1200Z 41.2N 22.2W 40 KT 45 MPH...POST-TROP/EXTRATROP 48H 28/0000Z 44.0N 21.1W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 29/0000Z 47.3N 20.9W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 30/0000Z...DISSIPATED $$ Forecaster Cangialosi

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Tropical Storm Pablo Forecast Discussion Number 1

2019-10-25 22:36:08| National Hurricane Center (Atlantic)

Issued at 500 PM AST Fri Oct 25 2019 000 WTNT43 KNHC 252036 TCDAT3 Tropical Storm Pablo Discussion Number 1 NWS National Hurricane Center Miami FL AL182019 500 PM AST Fri Oct 25 2019 High-resolution visible satellite imagery gave us a surprise today. A tropical cyclone has formed within a larger extratropical cyclone in the northeastern Atlantic. This is not unique and has occurred several times in the past, primarily during the latter part of the hurricane season. Pablo is a very small-scale tropical cyclone, but ASCAT data clearly show a well-defined but small circulation with 40-kt winds embedded within the larger low. This is the intensity assigned to the cyclone for this advisory. The cloud pattern consists of an eye-type feature surrounded by a ring of deep convection. Given the small size of the cyclone, and the baroclinic environment, the intensity forecast is highly uncertain. At this time, the NHC forecast calls for a small increase in the winds and for the cyclone to become extratropical in about 36 hours. However, this transition could occur sooner than anticipated. Pablo is currently moving toward the east-southeast at about 9 kt while embedded within the circulation of the larger extratropical low. Pablo should then turn toward the northeast with some increase in forward speed, as indicated by the multi-model consensus aids. In fact, all the models are in very good agreement, and the NHC forecast is in the middle of the guidance envelope. Given that Pablo is embedded within a large extratropical low, which itself is forecast to bring strong winds to the Azores, the Portuguese Institute for the Sea and Atmosphere (IPMA) has included the effects of this small cyclone in their products. Those products already account for the strong winds and high waves. FORECAST POSITIONS AND MAX WINDS INIT 25/2100Z 35.8N 32.2W 40 KT 45 MPH 12H 26/0600Z 35.3N 30.7W 45 KT 50 MPH 24H 26/1800Z 36.3N 26.8W 45 KT 50 MPH 36H 27/0600Z 40.0N 23.5W 45 KT 50 MPH 48H 27/1800Z 43.0N 21.5W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 28/1800Z 46.5N 20.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 29/1800Z...DISSIPATED $$ Forecaster Avila

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Tropical Storm Olga Forecast Discussion Number 2

2019-10-25 22:35:04| National Hurricane Center (Atlantic)

Issued at 400 PM CDT Fri Oct 25 2019 000 WTNT42 KNHC 252035 TCDAT2 Tropical Storm Olga Discussion Number 2 NWS National Hurricane Center Miami FL AL172019 400 PM CDT Fri Oct 25 2019 Although Tropical Depression Seventeen began looking less and less like a tropical cyclone in satellite imagery, scatterometer data and reports from an Air Force Reserve Hurricane Hunter aircraft indicate that so far the tropical cyclone remains just ahead of the approaching cold front, with the aircraft showing the front located about 25 n mi from the center in the southwestern quadrant. In addition, the aircraft and scatterometer data indicate that the cyclone's winds have increased to 35 kt in the northeastern quadrant. Based on this, the depression is upgraded to Tropical Storm Olga. It should be noted that a large area of 35-45 kt winds is occurring west of the cold front over the western Gulf of Mexico, although these winds are more due to the cold air surging across the Gulf than to the cyclone's circulation. Olga has begun its expected acceleration toward the north-northeast with the initial motion now 030/16. A deep-layer baroclinic trough over the southern Plains states should steer the cyclone generally north-northeastward with an additional increase in forward speed during the next couple of days. The center is expected to cross the northern Gulf coast tonight or Saturday morning and eventually reach the eastern Great Lakes by late Sunday. The new forecast track is nudged a little to the east of the previous one based on the initial position and motion through 36 h and an eastward shift in the guidance at 48 h. All indications are that Olga will complete extratropical transition during the next few hours as it merges with the cold front. The intensity forecast shows slight strengthening during the first 12 h based on the premise that the winds west of the cold front remain strong as they wrap into the circulation of Olga. The post-tropical low should weaken after landfall, and it is expected to dissipate just after the 48-h point. Key messages: 1. Since Olga is expected to merge with a cold front and become post-tropical by tonight, hazards related to wind, rainfall and coastal flooding will be covered by products issued by local National Weather Service forecast offices, available at weather.gov FORECAST POSITIONS AND MAX WINDS INIT 25/2100Z 26.3N 93.2W 35 KT 40 MPH 12H 26/0600Z 29.8N 91.7W 40 KT 45 MPH...POST-TROP/EXTRATROP 24H 26/1800Z 35.2N 89.8W 30 KT 35 MPH...POST-TROP/EXTRATROP 36H 27/0600Z 40.1N 86.4W 25 KT 30 MPH...POST-TROP/EXTRATROP 48H 27/1800Z 44.5N 81.5W 25 KT 30 MPH...POST-TROP/EXTRATROP 72H 28/1800Z...DISSIPATED $$ Forecaster Beven

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Tropical Depression Seventeen Forecast Discussion Number 1

2019-10-25 16:32:35| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Fri Oct 25 2019 000 WTNT42 KNHC 251432 TCDAT2 Tropical Depression Seventeen Discussion Number 1 NWS National Hurricane Center Miami FL AL172019 1000 AM CDT Fri Oct 25 2019 Satellite imagery indicates that the low pressure system in the western Gulf of Mexico has developed a well-defined circulation. In addition, a cluster of strong convection is located near and to the northeast of the low-level center. Thus, advisories are being initiated on Tropical Depression Seventeen. The initial intensity is set at 30 kt, and it is possible based on last night's scatterometer data that this is conservative. A deep-layer baroclinic trough over the southern Plains states should steer the cyclone north-northeastward with an increase in forward speed during the next couple of days, with the center crossing the northern Gulf coast tonight or Saturday morning. The track guidance is in good agreement, and the forecast track lies close to the various consensus models. A surface cold front associated with the baroclinic trough is quickly approaching the center of the depression, and the tropical cyclone is expected to merge with the front during the next 12 h. Based on this, the cyclone is expected to become a gale-force post-tropical low before it reaches the northern Gulf coast. The low should weaken after landfall, with dissipation expected just after 48 h. There is a chance that the system could briefly become a tropical storm this afternoon before it merges with the cold front. However, even if this occurs it will make little difference to the impacts on the northern Gulf coast. Key messages: 1. Since depression is expected to merge with a cold front and become post-tropical by tonight, hazards related to wind, rainfall and coastal flooding will be covered by products issued by local National Weather Service forecast offices, available at weather.gov FORECAST POSITIONS AND MAX WINDS INIT 25/1500Z 25.6N 94.4W 30 KT 35 MPH 12H 26/0000Z 28.2N 93.1W 35 KT 40 MPH...POST-TROP/EXTRATROP 24H 26/1200Z 32.6N 91.3W 30 KT 35 MPH...POST-TROP/EXTRATROP 36H 27/0000Z 38.1N 89.1W 25 KT 30 MPH...POST-TROP/EXTRATROP 48H 27/1200Z 43.2N 85.4W 20 KT 25 MPH...POST-TROP/EXTRATROP 72H 28/1200Z...DISSIPATED $$ Forecaster Beven

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