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Tropical Storm Kirk Forecast Discussion Number 15

2018-09-27 16:52:07| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Thu Sep 27 2018 451 WTNT42 KNHC 271452 TCDAT2 Tropical Storm Kirk Discussion Number 15 NWS National Hurricane Center Miami FL AL122018 1100 AM AST Thu Sep 27 2018 Increasing vertical shear is having a notable influence on the structure of Kirk, as visible satellite imagery shows that the low-level center of the cyclone is now exposed to the west of the main area of deep convection. Nonetheless, the Air Force Hurricane Hunters still found strong winds in that convection. In fact, based on SFMR and flight-level winds from the Hurricane Hunters, the advisory intensity of 45 kt may be a conservative estimate. With the increasing vertical decoupling of the vortex and even stronger shear associated with upper-level westerlies over the Caribbean Sea, weakening is likely over the next couple of days. Kirk should degenerate into a remnant low in 2 to 3 days, if not sooner. The official forecast is close to the multi-model intensity consensus, IVCN. The storm continues moving west-northwestward, with a current motion estimate of 285/13 kt. A mid-level high pressure area just to the east of Florida is likely to steer Kirk on a west-northwestward to westward course for the next few days. Some further slowing of forward speed is expected as the high weakens slightly. The NHC track forecast is very close to the latest HFIP corrected consensus prediction. Interests in the Lesser Antilles should bear in mind that, although Kirk is becoming disorganized, strong winds are still occurring over the eastern portion of the circulation. These winds are still likely to spread westward over the islands in the Tropical Storm Warning area later today. Higher winds are especially likely over elevated terrain. FORECAST POSITIONS AND MAX WINDS INIT 27/1500Z 13.8N 59.3W 45 KT 50 MPH 12H 28/0000Z 14.3N 61.0W 40 KT 45 MPH 24H 28/1200Z 14.9N 63.2W 35 KT 40 MPH 36H 29/0000Z 15.5N 65.4W 30 KT 35 MPH 48H 29/1200Z 15.9N 67.7W 25 KT 30 MPH 72H 30/1200Z 16.0N 72.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 01/1200Z...DISSIPATED $$ Forecaster Pasch

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Tropical Storm Kirk Forecast Discussion Number 14

2018-09-27 10:40:33| National Hurricane Center (Atlantic)

Issued at 500 AM AST Thu Sep 27 2018 162 WTNT42 KNHC 270840 TCDAT2 Tropical Storm Kirk Discussion Number 14 NWS National Hurricane Center Miami FL AL122018 500 AM AST Thu Sep 27 2018 Kirk has not changed much overnight. Although the storm is producing a large area of deep convection, the cloud pattern is not very well organized with the center located near the southwestern edge of the thunderstorms. This asymmetric cloud pattern is due to about 20 kt of southwesterly shear. The Air Force Hurricane Hunters passed through the northeastern quadrant of Kirk a few hours ago and found winds to support the same intensity of 45 kt. In addition, quality control of a ship report that came in around the same time also supports that intensity. Another Air Force plane is scheduled to investigate Kirk later this morning. A large fetch of strong upper-level westerly or southwesterly winds are over the entire Caribbean Sea, and Kirk will be moving into these conditions during the next few days. These very hostile winds aloft should cause Kirk to steadily weaken, decouple, and ultimately dissipate in 3 or 4 days. The GFS and ECMWF models suggest that dissipation could occur even sooner. The intensity models are in good agreement, and the NHC forecast is the same as the previous one. Center fixes from the Air Force reconnaissance aircraft indicate that Kirk is moving west-northwestward at 14 kt. A continued west-northwest motion but at a slower pace is expected during the next few days as Kirk moves on the south side of a low- to mid-level ridge. The latest models have not changed much, and the NHC track forecast lies near the middle of the guidance envelope. This forecast takes Kirk across the Lesser Antilles later today as a tropical storm. FORECAST POSITIONS AND MAX WINDS INIT 27/0900Z 13.5N 58.3W 45 KT 50 MPH 12H 27/1800Z 14.2N 60.2W 45 KT 50 MPH 24H 28/0600Z 14.9N 62.5W 40 KT 45 MPH 36H 28/1800Z 15.6N 64.7W 35 KT 40 MPH 48H 29/0600Z 16.0N 67.0W 30 KT 35 MPH 72H 30/0600Z 16.3N 71.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 01/0600Z...DISSIPATED $$ Forecaster Cangialosi

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Hurricane Rosa Forecast Discussion Number 9

2018-09-27 10:40:02| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Thu Sep 27 2018 748 WTPZ45 KNHC 270839 TCDEP5 Hurricane Rosa Discussion Number 9 NWS National Hurricane Center Miami FL EP202018 300 AM MDT Thu Sep 27 2018 The cloud pattern is a little more impressive with plenty of deep convection and a well-defined cyclonically-curved band south of the center. There is no evidence of an eye yet in conventional IR imagery. Satellite intensity estimates from all agencies, however, are unanimously 4.5 on the Dvorak scale, so the intensity is kept at 75 kt. Both atmospheric and oceanic conditions are favorable for intensification with the possibility of rapid strengthening within the next 12 to 24 hours, although intensity guidance is not as aggressive as in earlier runs. The NHC forecast follows closely the intensity consensus and is very similar to the previous one. Beyond 3 days, Rosa should be over cooler waters, and by the time it reaches the northern Baja California peninsula, the cyclone should have weakened to a tropical storm. Rosa is moving westward or 270 degrees at 10 kt steered by the deep easterly flow around a subtropical ridge. Rosa will soon reach the southwestern edge of the high and will begin to move toward the northwest and northward as an eastward moving mid-level trough erodes the high to the north. Rosa should then turn toward the northeast ahead of the trough by the end of the forecast period. This is the solution provided by most of the track models which all turn the cyclone northward and then northeastward. The NHC forecast is in the middle of the guidance envelope and is in between the corrected consensus HCCA and the multi-model aids. FORECAST POSITIONS AND MAX WINDS INIT 27/0900Z 17.1N 114.1W 75 KT 85 MPH 12H 27/1800Z 17.2N 115.6W 90 KT 105 MPH 24H 28/0600Z 17.5N 117.0W 100 KT 115 MPH 36H 28/1800Z 17.8N 118.0W 105 KT 120 MPH 48H 29/0600Z 18.8N 118.8W 105 KT 120 MPH 72H 30/0600Z 22.0N 119.0W 90 KT 105 MPH 96H 01/0600Z 25.5N 118.0W 60 KT 70 MPH 120H 02/0600Z 29.0N 116.0W 45 KT 50 MPH $$ Forecaster Avila

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Tropical Storm Kirk Forecast Discussion Number 13

2018-09-27 04:52:03| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Wed Sep 26 2018 339 WTNT42 KNHC 270251 TCDAT2 Tropical Storm Kirk Discussion Number 13 NWS National Hurricane Center Miami FL AL122018 1100 PM AST Wed Sep 26 2018 Strengthening vertical shear is beginning to take its toll on Kirk, with the low-level center displaced to the west of the deep convection. An Air Force Reserve Hurricane Hunter aircraft found that the central pressure has risen to 1002 mb, with maximum 850 mb flight-level winds of 56 kt and believable SFMR winds as high as 44 kt. Based on these wind data, Kirk's initial intensity is lowered to 45 kt. Vertical shear is forecast to increase further, reaching over 30 kt in about 24 hours, which should cause Kirk to continue weakening over the next day or two. And, based on the latest global model guidance, the cyclone could open up into a trough any time after passing by the Lesser Antilles. The new NHC intensity forecast is mainly an update of the previous one to account for the lower initial intensity, and it continues to closely follow the intensity consensus, IVCN, and the HCCA guidance. Dissipation is now shown by day 4, but as mentioned above, this could occur a lot sooner. Kirk appears to have slowed down just a little, with an initial motion toward the west-northwest, or 285/14 kt. Ridging to the north should maintain Kirk on this general trajectory, with perhaps just a slight deceleration as it moves into the eastern Caribbean Sea. There are some speed differences among the models, with the ECMWF showing a weaker and faster system, while the GFS shows a slightly stronger and slower system. The NHC track forecast is between these two solutions and is closest to the HCCA model. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 13.0N 57.0W 45 KT 50 MPH 12H 27/1200Z 13.6N 58.6W 45 KT 50 MPH 24H 28/0000Z 14.4N 60.9W 40 KT 45 MPH 36H 28/1200Z 15.1N 63.3W 35 KT 40 MPH 48H 29/0000Z 15.6N 65.6W 30 KT 35 MPH 72H 30/0000Z 16.0N 69.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 01/0000Z...DISSIPATED $$ Forecaster Berg

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Hurricane Rosa Forecast Discussion Number 8

2018-09-27 04:35:33| National Hurricane Center (East Pacific)

Issued at 900 PM MDT Wed Sep 26 2018 884 WTPZ45 KNHC 270235 TCDEP5 Hurricane Rosa Discussion Number 8 NWS National Hurricane Center Miami FL EP202018 900 PM MDT Wed Sep 26 2018 During the past several hours, the convective pattern of Rosa has become more symmetric, and perhaps an eye is trying to emerge in the last few satellite images. Overall, Rosa appears somewhat stronger than the past advisory, so the initial wind speed is slightly raised to 75 kt- near the TAFB Dvorak estimate and the CIMSS ADT. The hurricane has been steadily strengthening over the past day, and, with conducive atmospheric and oceanic conditions in the forecast for the next couple of days, this trend should continue. A more rapid intensification period is possible if the inner core becomes better defined. Curiously, the intensity guidance has come in lower than the last cycle, despite no obvious inhibiting factors from all of the global models. I'd rather keep the high forecast of my predecessor until the reasons for this lower peak intensity become clear. In addition, the corrected-consensus guidance is higher than the rest of the aids, supporting the stronger forecast. By day 3 weakening should commence as Rosa moves over cooler waters, and rapid weakening is possible by the end of the forecast while the cyclone encounters high shear over quite cool waters. Rosa has turned westward, now moving at about 10 kt. A mid-level high over the southwestern United States should steer the hurricane on this general course for the next day or so. After that time, the high shifts eastward due to a series of troughs approaching the west coast of the United States, causing Rosa to gradually turn toward the northwest by Friday, north on Saturday and to the northeast by Monday. There are still some pretty large speed differences in the models at long range, with the GFS-based guidance a lot faster than the ECMWF or UKMET models and their ensembles. There are no obvious reasons to favor either solution at this time, so the track forecast will stay close to the dynamical model consensus and the previous forecast. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 16.9N 113.1W 75 KT 85 MPH 12H 27/1200Z 17.0N 114.6W 90 KT 105 MPH 24H 28/0000Z 17.1N 116.2W 100 KT 115 MPH 36H 28/1200Z 17.6N 117.4W 105 KT 120 MPH 48H 29/0000Z 18.4N 118.2W 110 KT 125 MPH 72H 30/0000Z 21.2N 119.2W 90 KT 105 MPH 96H 01/0000Z 24.6N 118.6W 70 KT 80 MPH 120H 02/0000Z 28.0N 116.0W 45 KT 50 MPH $$ Forecaster Blake

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