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Tropical Storm Alvin Forecast Discussion Number 13

2019-06-28 22:32:54| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Fri Jun 28 2019 000 WTPZ41 KNHC 282032 TCDEP1 Tropical Storm Alvin Discussion Number 13 NWS National Hurricane Center Miami FL EP012019 200 PM PDT Fri Jun 28 2019 Alvin is rapidly weakening due to motion over sea surface temperatures of 23-24C and increasing southwesterly vertical wind shear, with the low-level center now partly exposed at the southern edge of the weakening convective mass. The initial intensity is reduced to 45 kt based on a blend of recent ASCAT data and subjective satellite intensity estimates. Continued rapid weakening is expected, and Alvin is forecast to become a remnant low in about 24 h and dissipate completely after 36 h. The initial motion is 310/13. The cyclone should continue generally northwestward for the next 12-18 h due to flow around a mid-level ridge to the north. After that time, the weakening and increasingly shallow system should turn west-northwestward as the low-level winds become the predominant steering mechanism. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 19.7N 118.6W 45 KT 50 MPH 12H 29/0600Z 20.7N 120.0W 35 KT 40 MPH 24H 29/1800Z 21.5N 121.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 30/0600Z 22.0N 123.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 30/1800Z...DISSIPATED $$ Forecaster Beven

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Tropical Storm Alvin Forecast Discussion Number 12

2019-06-28 16:35:21| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Fri Jun 28 2019 456 WTPZ41 KNHC 281435 TCDEP1 Tropical Storm Alvin Discussion Number 12 NWS National Hurricane Center Miami FL EP012019 800 AM PDT Fri Jun 28 2019 Alvin continues to lose organization as a steady weakening trend has commenced. The satellite presentation has become more ragged and the center is now very close to the southwestern edge of the deep convection. Satellite intensity estimates continue to decrease, with a blended average indicating a 55 kt initial intensity for this advisory. Alvin is already over SSTs of 24 C and will move over even cooler waters over the next 36 hours. In addition, the latest guidance depicts southwesterly shear of 15 to 20 kt impacting the circulation, and this is forecast to increase to over 30 kt in 24 hours. These factors, along with Alvin moving into an increasingly stable atmospheric environment, will result in continued steady weakening into this weekend. By Saturday night, Alvin is expected to become devoid of deep convection, and the cyclone is forecast to dissipate by Sunday. Alvin accelerated slightly overnight, with an initial motion of 305/14 kt. This faster motion is expected to be only temporary and the official track forecast is near the clustering of the consensus aids. Alvin will be steered around the southwestern periphery of mid-level ridging to its north through today. Thereafter, a much weaker cyclone will become steered by the lower level environmental flow, which will result in a turn to the west-northwest and decrease in forward speed tonight into Saturday. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 19.0N 117.7W 55 KT 65 MPH 12H 29/0000Z 20.1N 119.3W 45 KT 50 MPH 24H 29/1200Z 21.0N 121.0W 35 KT 40 MPH 36H 30/0000Z 21.6N 122.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 30/1200Z...DISSIPATED $$ Forecaster Latto/Beven

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Tropical Storm Alvin Forecast Discussion Number 11

2019-06-28 10:36:46| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Fri Jun 28 2019 000 WTPZ41 KNHC 280836 TCDEP1 Tropical Storm Alvin Discussion Number 11 NWS National Hurricane Center Miami FL EP012019 200 AM PDT Fri Jun 28 2019 Alvin's satellite presentation has begun to degrade overnight with the overall cloud pattern becoming elongated from southwest to northeast. Earlier ASCAT data indicated that the center was located within the southwestern portion of the main convective mass, suggesting that southwesterly shear has caused the system to become less symmetric. Subjective Dvorak T-numbers from SAB and TAFB have started to decrease, and a blend of the various satellite intensity estimates yields an initial wind speed of 60 kt for this advisory. Increasing southwesterly shear and cooler waters ahead of the storm are expected to cause rapid weakening during the next 24 to 36 hours. Since Alvin is a small cyclone, it is likely to suffer from the affects of the hostile environment more quickly. As a result, the NHC intensity forecast calls for a faster rate of weakening than indicated by the statistical SHIPS/LGEM models and is closest to the latest Florida State Superensemble. The cyclone is forecast to degenerate into a remnant low on Saturday and it should dissipate shortly thereafter. The initial motion estimate is 305/13 kt. The track forecast philosophy remains the same as the previous advisory. Alvin should continue to move around the western periphery of a subtropical ridge during the next couple of days, with the weakening cyclone turning more westward and decelerating. The latest NHC track forecast is near the various consensus aids and is essentially an update of the previous official forecast. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 18.0N 116.3W 60 KT 70 MPH 12H 28/1800Z 19.2N 118.0W 55 KT 65 MPH 24H 29/0600Z 20.3N 119.8W 40 KT 45 MPH 36H 29/1800Z 20.9N 121.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 30/0600Z 21.3N 122.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 01/0600Z...DISSIPATED $$ Forecaster Brown

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Hurricane Alvin Forecast Discussion Number 10

2019-06-28 04:32:14| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Thu Jun 27 2019 000 WTPZ41 KNHC 280232 TCDEP1 Hurricane Alvin Discussion Number 10 NWS National Hurricane Center Miami FL EP012019 800 PM PDT Thu Jun 27 2019 Somewhat surprisingly, Alvin has strengthened into a hurricane this evening. The diminutive system is exhibiting a rather symmetric CDO with very deep convection bursting near the center. Microwave images show a small eye about 10 n mi in diameter. Subjective Dvorak classifications from both TAFB and SAB, along with objective intensity estimates from UW-CIMSS, support a current intensity of 65 kt. Alvin is not expected to maintain its intensity for very long. Within 12 to 24 hours, the cyclone should encounter significantly stronger southwesterly shear and SSTs below 24 deg C. These hostile environmental factors should bring about rapid weakening, as supported by essentially all of the numerical guidance. Alvin is expected to degenerate into a remnant low on Saturday. The hurricane is moving a little to the right and slightly faster than previous estimates, with an initial motion of about 305/14 kt. Alvin should continue to move near the western periphery of a subtropical ridge for the next 48 hours, with the weakening cyclone gradually turning toward the left and decelerating. The official track forecast is very close to the latest corrected dynamical model consensus. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 17.4N 115.4W 65 KT 75 MPH 12H 28/1200Z 18.7N 117.1W 60 KT 70 MPH 24H 29/0000Z 20.1N 119.1W 45 KT 50 MPH 36H 29/1200Z 20.9N 120.6W 35 KT 40 MPH 48H 30/0000Z 21.5N 121.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 01/0000Z...DISSIPATED $$ Forecaster Pasch

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Tropical Storm Alvin Forecast Discussion Number 9

2019-06-27 22:32:09| National Hurricane Center (East Pacific)

Issued at 300 PM MDT Thu Jun 27 2019 000 WTPZ41 KNHC 272032 TCDEP1 Tropical Storm Alvin Discussion Number 9 NWS National Hurricane Center Miami FL EP012019 300 PM MDT Thu Jun 27 2019 A pair of timely ASCAT passes just before 1800 UTC indicate that Alvin has strengthened a little more. Multiple 45-50 kt wind vectors were present in the northwest quadrant of the cyclone in both passes. The intensity of the tropical storm has been increased to 55 kt since the ASCAT instrument is likely undersampling the strongest winds of this small tropical storm. Most of the intensity models indicate that Alvin has reached its peak intensity, however, the HWRF and GFS suggest that Alvin could still squeak out a little more intensification during the next 12 h or so. While I can't rule out that Alvin could get a little stronger tonight, its window for strengthening is likely closing soon. The cyclone's infrared cloud signature has already taken on a shear pattern, and GFS- and ECMWF-based SHIPS diagnostics suggest that the shear should steadily increase during the next 48 h. Furthermore, the tropical storm is quickly approaching cooler waters. Nearly all of the models show Alvin degenerating into a remnant low within about 48 h and dissipating soon thereafter, and the NHC forecast reflects this. The initial motion of Alvin is still 300/12 kt. No changes of significance were made to the NHC track forecast which continues to closely follow HCCA and TVCN. Alvin should continue on this general heading for another 24 hours or so, before gradually turning westward as it degenerates into a remnant low over the weekend. FORECAST POSITIONS AND MAX WINDS INIT 27/2100Z 16.6N 114.2W 55 KT 65 MPH 12H 28/0600Z 17.7N 115.9W 55 KT 65 MPH 24H 28/1800Z 19.3N 118.0W 45 KT 50 MPH 36H 29/0600Z 20.3N 119.9W 35 KT 40 MPH 48H 29/1800Z 20.9N 121.3W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 30/1800Z...DISSIPATED $$ Forecaster Zelinsky

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