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Subtropical Storm Leslie Forecast Discussion Number 10

2018-09-28 22:47:45| National Hurricane Center (Atlantic)

Issued at 500 PM AST Fri Sep 28 2018 295 WTNT43 KNHC 282047 TCDAT3 Subtropical Storm Leslie Discussion Number 10 NWS National Hurricane Center Miami FL AL132018 500 PM AST Fri Sep 28 2018 Central convection associated with Post-Tropical Storm Leslie has gradually increased during the last couple of days and is now organized into a group of bands that wraps most of the way around the center. In addition, scatterometer data show that the cyclone has lost much of its large baroclinic wind field, and that the radius of maximum winds has contracted from 120-180 n mi yesterday to 90 n mi or less today. While the storm has also developed a warm core and shed some of its baroclinic characteristics, it is embedded in a large deep-layer low pressure system, and thus it is designated subtropical instead of tropical. The initial intensity is set at 45 kt based on the scatterometer data. Leslie has been moving generally westward for the the past few days. The large-scale models forecast a general southwesterly motion for the next 3-4 days as the cyclone is steered by a segment of the subtropical ridge to its west and another large deep-layer low forming to its east over the eastern Atlantic, with a decrease in forward speed near the end of the forecast period as the ridge to the west weakens. The forecast guidance is tightly clustered through 120 h, and the forecast track is near the center of the guidance envelope and the consensus models. The forecast track takes the center of Leslie over increasing sea surface temperatures during the next several days, although the temperatures may not be as warm as those indicated in the SHIPS model. The global models suggest that little change in strength will occur during the first 48-72 h as Leslie gradually develops the upper-level outflow pattern of a tropical cyclone and transitions to a tropical storm. After that time, they are in good agreement that the cyclone will strengthen. Based on this, the intensity forecast shows only modest intensification during the first 48 h, followed by strengthening to a probably conservative 60 kt. The forecast also calls for transition to a tropical storm between 48-72 h, with the caveat that this could occur earlier. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 36.1N 48.1W 45 KT 50 MPH 12H 29/0600Z 35.4N 49.6W 45 KT 50 MPH 24H 29/1800Z 34.4N 51.2W 45 KT 50 MPH 36H 30/0600Z 33.8N 52.2W 50 KT 60 MPH 48H 30/1800Z 33.2N 53.1W 50 KT 60 MPH 72H 01/1800Z 32.5N 54.5W 55 KT 65 MPH...TROPICAL STORM 96H 02/1800Z 31.0N 56.0W 60 KT 70 MPH 120H 03/1800Z 31.0N 57.0W 60 KT 70 MPH $$ Forecaster Beven

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Tropical Storm Kirk Forecast Discussion Number 20

2018-09-28 22:35:45| National Hurricane Center (Atlantic)

Issued at 500 PM AST Fri Sep 28 2018 981 WTNT42 KNHC 282035 TCDAT2 Tropical Storm Kirk Discussion Number 20 NWS National Hurricane Center Miami FL AL122018 500 PM AST Fri Sep 28 2018 Kirk is barely meeting the criteria for a tropical cyclone. The small low-level center is still exposed well to the west of most of the deep convection. The last fix from the earlier Air Force Reserve Hurricane Hunter mission found that the cyclone was still closed, but the maximum winds had decreased to near 35 kt. Since it seems likely that winds of this magnitude are still occuring in the convection to the east of Kirk, the system is maintained as a tropical storm for this advisory. Another reconnaissance mission is scheduled for tonight, and it should give a better estimate of the intensity of Kirk, and if the cyclone still has a well-defined surface circulation. No significant changes have been made to the track or intensity forecasts. Kirk is expected to move generally west-northwestward to northwestward over the next 12 hours or so while weakening due to the continued effects of strong westerly wind shear. By tomorrow morning, the cyclone will likely have degenerated into a trough of low pressure. Even though Kirk is weakening, heavy rains are expected over St Croix and eastern Puerto Rico during the next day or two while Kirk or its remnants pass to the south of those islands. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 14.7N 64.7W 35 KT 40 MPH 12H 29/0600Z 15.3N 66.2W 30 KT 35 MPH 24H 29/1800Z...DISSIPATED $$ Forecaster Zelinsky

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Hurricane Rosa Forecast Discussion Number 14

2018-09-28 17:18:13| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Fri Sep 28 2018 903 WTPZ45 KNHC 281517 CCA TCDEP5 Hurricane Rosa Discussion Number 14...Corrected NWS National Hurricane Center Miami FL EP202018 800 AM PDT Fri Sep 28 2018 Corrected typo in second paragraph. Cloud tops surrounding the distinct eye of Rosa have warmed considerably over the past few hours. A recent SSMI overpass showed a distinct double eyewall structure, and this is likely the reason for the degradation of Rosa's appearance. Dvorak intensity estimates from TAFB and SAB have decreased as a result, and the initial intensity has been therefore decreased to 120 kt. Given the continued warming of cloud tops since 1200 UTC, it is possible that Rosa has weakened a little more than this. Since an eyewall replacement cycle is ongoing, Rosa is no longer expected to intensify. In the short term, some additional weakening is likely, typical of major hurricanes undergoing eyewall replacements. If this process completes within the next 24 hours, there will be some opportunity for the hurricane to re-intensify while the shear is low and the hurricane remains over warm SSTs. However, steady weakening is anticipated beginning Saturday night since the cyclone is forecast to cross over much cooler SSTs. By 96 h, a weaker Rosa will likely approach the northern west coast of the Baja California peninsula and the resulting interaction with land will likely cause the cyclone to dissipate. It is worth noting that a farther northwest track would likely result in Rosa weakening faster than currently indicated, while a farther southeast track could allow Rosa to maintain a slightly stronger circulation as it crosses the northern Gulf of California. Rosa has begun its long-anticipated turn toward the northwest, and the initial motion estimate is 315/6 kt. The track models remain in good agreement that Rosa will gradually turn toward the north, and then north-northeast over the next few days ahead of an approaching mid- to upper-level trough to the northwest. No significant changes were made to the official track forecast, but it has been adjusted slightly to the left (or northwest) at most times, in line with the latest consensus guidance. Even though the NHC forecast calls for the surface circulation of Rosa to dissipate after making landfall along the northern Baja California coast, its associated moisture is expected to spread northeastward through parts of the southwest United States. For more information about potential rainfall in that area, please see products from the Weather Prediction Center and your local NWS forecast office. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 17.2N 117.5W 120 KT 140 MPH 12H 29/0000Z 17.8N 118.1W 110 KT 125 MPH 24H 29/1200Z 19.2N 118.6W 105 KT 120 MPH 36H 30/0000Z 21.0N 118.9W 95 KT 110 MPH 48H 30/1200Z 23.0N 118.8W 80 KT 90 MPH 72H 01/1200Z 26.7N 117.4W 55 KT 65 MPH 96H 02/1200Z 31.6N 115.0W 35 KT 40 MPH...INLAND 120H 03/1200Z...DISSIPATED $$ Forecaster Zelinsky

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Tropical Storm Kirk Forecast Discussion Number 19

2018-09-28 16:45:14| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Fri Sep 28 2018 287 WTNT42 KNHC 281445 TCDAT2 Tropical Storm Kirk Discussion Number 19 NWS National Hurricane Center Miami FL AL122018 1100 AM AST Fri Sep 28 2018 Kirk has become less organized since the last advisory, with satellite imagery showing that the low-level center is now exposed well to the west-northwest of the remaining deep convection. Reports from an Air Force Reserve Hurricane Hurricane Hunter aircraft indicate that the winds have decreased to near 40 kt and that the central pressure has risen to near 1007 mb. The aircraft also reports that the circulation is losing definition in the southwestern quadrant. Kirk should continue to weaken due to the effects of 30 kt of westerly vertical shear, and the NHC forecast continues to call for dissipation just after 24 h. As noted in the previous discussion, there is a chance dissipation could occur earlier than currently forecast. The center has jogged back to the west-northwest during the past few hours, which results in an uncertain initial motion of 285/11. Kirk should move generally west-northwestward on the south side of the subtropical ridge until dissipation. Even though Kirk is weakening and moving away from the Lesser Antilles, the associated gusty winds and rains should continue affecting the islands today. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 13.8N 63.6W 40 KT 45 MPH 12H 29/0000Z 14.2N 65.3W 35 KT 40 MPH 24H 29/1200Z 14.8N 67.6W 25 KT 30 MPH 36H 30/0000Z...DISSIPATED $$ Forecaster Beven

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Tropical Storm Kirk Forecast Discussion Number 18

2018-09-28 10:32:40| National Hurricane Center (Atlantic)

Issued at 500 AM AST Fri Sep 28 2018 002 WTNT42 KNHC 280832 TCDAT2 Tropical Storm Kirk Discussion Number 18 NWS National Hurricane Center Miami FL AL122018 500 AM AST Fri Sep 28 2018 Kirk is a highly sheared cyclone with most of the associated weather well east of the center. Despite the lack of organization of the cloud pattern, a reconnaissance plane a few hours ago, reported winds to support an initial intensity of 45 kt. Another plane will be investigating Kirk early this morning and will determine how much the cyclone has weakened. The upper-level winds are highly unfavorable across the entire Caribbean basin, and the most likely scenario is for Kirk to open up into a trough sooner rather than later as indicated by most of the global models. The NHC forecast keeps the cyclone for another 24 hours, but dissipation could occur much earlier. Satellite imagery, radar from Martinique, and plane fixes indicate that Kirk jogged toward the west-southwest earlier. This could be an indication that the center is becoming less defined, but the bottom line is that the system as a whole is expected to move westward about 10 kt since it is embedded within the trade winds. This is the solution provided by most of the models, which all show a weakening trough propagating westward across the eastern and central Caribbean Sea. Interests in the Lesser Antilles should continue to bear in mind that most of the weather associated with Kirk is displaced to the east of the center. These winds and rains are still likely to continue spreading westward over the islands in the Tropical Storm Warning area for the next several hours. Higher winds are anticipated especially over elevated terrain. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 13.2N 62.5W 45 KT 50 MPH 12H 28/1800Z 13.2N 64.0W 40 KT 45 MPH 24H 29/0600Z 14.0N 66.5W 30 KT 35 MPH 36H 29/1800Z...DISSIPATED $$ Forecaster Avila

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