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Tropical Storm Xavier Forecast Discussion Number 6

2018-11-04 03:37:26| National Hurricane Center (East Pacific)

Issued at 1000 PM CDT Sat Nov 03 2018 000 WTPZ45 KNHC 040237 TCDEP5 Tropical Storm Xavier Discussion Number 6 NWS National Hurricane Center Miami FL EP252018 1000 PM CDT Sat Nov 03 2018 Xavier's overall structure has not changed since this afternoon. The tropical storm is still strongly sheared and deep convection is primarily occurring to the northeast of its low-level center. Recent objective and subjective intensity estimates range from 45 to 50 kt. Earlier ASCAT data explicitly contained several vectors near 45 kt, but the instrument could have under-sampled the maximum winds. Based on all these data, 50 kt seems most representative of the tropical storm's intensity at this time. Regardless of Xavier's exact maximum winds, it is likely nearing its peak intensity now. Some slight additional strengthening in the short term can not be ruled out, however the global models indicate that strong wind shear will continue through the forecast period and the flow aloft will become less supportive for convection by late Sunday or early Monday. All of the intensity models forecast that Xavier will begin to weaken in about 24 h. By 96 h, if not sooner, the dynamical models indicate that Xavier will lose all deep convection and become a remnant low. Virtually no change was made to the official intensity forecast, which is merely an update of the previous advisory. Xavier is now moving toward the northeast, and the initial motion estimate is 035/6 kt. With the continued exception of the UKMET model, the typically reliable track guidance is in good agreement on the track of the tropical storm. The cyclone will likely turn northward tonight or tomorrow, and is then forecast to turn steadily westward in another day or two as it weakens and becomes vertically shallow. The UKMET does not show this turn and shows a stronger/deeper Xavier that moves farther north, though this scenario appears unlikely given the strong agreement among the intensity models that Xavier will weaken. Only minor adjustments were made to the NHC track forecast, which blends the previous official forecast with the HCCA and GFEX consensus aids at most forecast hours. FORECAST POSITIONS AND MAX WINDS INIT 04/0300Z 16.1N 105.7W 50 KT 60 MPH 12H 04/1200Z 16.7N 105.6W 50 KT 60 MPH 24H 05/0000Z 17.4N 105.9W 45 KT 50 MPH 36H 05/1200Z 17.8N 106.6W 40 KT 45 MPH 48H 06/0000Z 17.9N 107.7W 35 KT 40 MPH 72H 07/0000Z 18.1N 110.1W 30 KT 35 MPH 96H 08/0000Z 18.3N 112.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 09/0000Z 18.5N 115.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Zelinsky

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Tropical Storm Xavier Forecast Discussion Number 5

2018-11-03 21:40:28| National Hurricane Center (East Pacific)

Issued at 300 PM MDT Sat Nov 03 2018 000 WTPZ45 KNHC 032040 TCDEP5 Tropical Storm Xavier Discussion Number 5 NWS National Hurricane Center Miami FL EP252018 300 PM MDT Sat Nov 03 2018 Xavier continues to show a sheared cloud pattern in conventional satellite imagery this afternoon, with the low-level center located near or just southwest of the main convective mass. The various subjective and objective satellite intensity estimates are near 45 kt, and recent scatterometer data also indicate winds near 45 kt. Thus, the initial intensity remains at that value. Analyses from CIMSS and from the SHIPS model indicate that Xavier is still in an environment of 20-25 kt of southwesterly vertical shear. There is little change in the intensity forecast philosophy from the last advisory. During the next 12-24 h, the dynamical models suggest that an upper-level trough located to the north and west of Xavier should provide upper-level divergence over the cyclone. This could allow some additional strengthening despite the ongoing shear. After that time, the trough is forecast to dissipate, leaving the tropical storm in an area of upper-level convergence, moderate to strong shear, and a dry surrounding air that should cause it to weaken. Based on this evolution, the intensity forecast calls for a little more strengthening early in the forecast, followed by gradual weakening through the remainder of the forecast period. As in the previous forecast, Xavier is expected to degenerate to a remnant low in about 96 h. The forecast again follows the overall trend of the intensity guidance and lies near the upper edge of the guidance through 48 h. The initial motion is now 060/8. As mentioned previously, Xavier should turn northeastward and then northward during the next 24 h toward a weakness in the subtropical ridge created by the aforementioned trough. As Xavier weakens and becomes a shallow system, the cyclone should turn toward the west-northwest and west as it is steered by the low-level flow to the south of the subtropical ridge. All of the dynamical models follow this scenario except for the UKMET, which shows a much more northward motion toward the southern Gulf of California. The new forecast track will follow the model consensus in showing the westward motion, and the new NHC forecast track is similar to the previous track. FORECAST POSITIONS AND MAX WINDS INIT 03/2100Z 15.6N 106.1W 45 KT 50 MPH 12H 04/0600Z 16.1N 105.7W 50 KT 60 MPH 24H 04/1800Z 16.9N 105.7W 50 KT 60 MPH 36H 05/0600Z 17.3N 106.1W 45 KT 50 MPH 48H 05/1800Z 17.5N 106.8W 40 KT 45 MPH 72H 06/1800Z 18.0N 109.5W 30 KT 35 MPH 96H 07/1800Z 18.0N 112.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 08/1800Z 18.5N 114.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Beven

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Tropical Storm Xavier Forecast Discussion Number 4

2018-11-03 15:34:25| National Hurricane Center (East Pacific)

Issued at 900 AM MDT Sat Nov 03 2018 000 WTPZ45 KNHC 031434 TCDEP5 Tropical Storm Xavier Discussion Number 4 NWS National Hurricane Center Miami FL EP252018 900 AM MDT Sat Nov 03 2018 Although Xavier is being affected by 20-25 kt of westerly vertical shear, the cyclone continues to generate a large burst of convection and the low-level center is now located under the southwestern edge of the convective mass. The initial intensity is increased to 45 kt, which is at the upper end of the various satellite intensity estimates. During the next 24 h, the dynamical models suggest that an upper-level trough located to the north and west of Xavier should provide upper-level divergence over the cyclone. This could allow some additional strengthening despite the ongoing shear. After that time, the trough is forecast to dissipate, leaving the tropical storm in an area of upper-level convergence and moderate to strong shear that should cause it to weaken. Based on this evolution, the intensity forecast calls for a little more strengthening during the next 12-24 h, followed by gradual weakening through the remainder of the forecast period, with the cyclone becoming a remnant low in about 96 h. The forecast follows the overall trend of the intensity guidance and lies near the upper edge of the guidance. Based on a combination of conventional and microwave satellite fixes, the initial motion is estimated to be 060/7. There is again little change to the forecast track philosophy. Xavier should turn northeastward and then northward during the next 24 h toward a weakness in the subtropical ridge created by the aforementioned trough. As Xavier weakens and becomes a shallow system, the cyclone should turn toward the west-northwest and west as it is steered by the low-level flow to the south of the subtropical ridge. The new forecast track is nudged just a little to the east and north of the previous track, but it remains close to the various consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 03/1500Z 15.3N 107.0W 45 KT 50 MPH 12H 04/0000Z 15.8N 106.4W 50 KT 60 MPH 24H 04/1200Z 16.6N 106.0W 50 KT 60 MPH 36H 05/0000Z 17.3N 106.1W 45 KT 50 MPH 48H 05/1200Z 17.4N 106.5W 40 KT 45 MPH 72H 06/1200Z 17.5N 108.0W 30 KT 35 MPH 96H 07/1200Z 17.5N 111.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 08/1200Z 18.0N 113.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Beven

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Tropical Storm Xavier Forecast Discussion Number 3

2018-11-03 09:36:51| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Sat Nov 03 2018 000 WTPZ45 KNHC 030836 TCDEP5 Tropical Storm Xavier Discussion Number 3 NWS National Hurricane Center Miami FL EP252018 300 AM MDT Sat Nov 03 2018 A large burst of deep convection has developed over the northeastern and eastern portions of Xavier's circulation overnight. An earlier GMI microwave overpass indicated that the center was located near the southwestern edge of the convection, but there was evidence of an increase in banding over the northeastern portion of the storm. Dvorak data T-numbers from TAFB and SAB were T2.5 and T3.0, respectively, so the initial intensity has been increased to 40 kt for this advisory. Xavier is expected to remain embedded within an area of moderate to strong southwesterly shear during the next 24 to 36 hours, and these conditions are likely to prevent significant strengthening. Although the statistical guidance shows no additional intensification, the dynamical models deepen the system over the next day or so, and the NHC forecast calls for a slight increase in wind speed today, followed by little change in strength through Sunday. This is in good agreement with the latest HFIP corrected consensus model. By 48 hours the shear is expected to become even stronger, and as a result, gradual weakening should occur thereafter. Xavier is forecast to degenerate into a remnant low by day 4, if not sooner. The aforementioned microwave pass was very helpful in locating the center of Xavier. Based on that data and recent satellite fixes, the initial motion estimate is east-northeastward at about 6 kt. The track forecast reasoning has not changed from the previous advisory. Xavier should turn northeastward, then northward by tonight toward a weakness in the subtropical ridge created by a deep-layer trough over central Mexico. After Xavier weakens, the cyclone should turn toward west-northwestward or westward as it is steered by the low-level flow. Since there is still a fair amount of spread among the track models as to how far north Xavier will move before it weakens and turns westward, the NHC track is close to the various consensus aids at 48 hours and beyond. Most of the track models have trended a little faster after 48 hours, and the official forecast has been adjusted accordingly. FORECAST POSITIONS AND MAX WINDS INIT 03/0900Z 14.7N 107.7W 40 KT 45 MPH 12H 03/1800Z 15.2N 107.0W 45 KT 50 MPH 24H 04/0600Z 16.0N 106.4W 45 KT 50 MPH 36H 04/1800Z 16.6N 106.3W 45 KT 50 MPH 48H 05/0600Z 17.1N 106.5W 40 KT 45 MPH 72H 06/0600Z 17.5N 107.7W 30 KT 35 MPH 96H 07/0600Z 17.6N 110.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 08/0600Z 18.0N 112.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown

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Tropical Storm Xavier Forecast Discussion Number 2

2018-11-03 03:33:52| National Hurricane Center (East Pacific)

Issued at 900 PM MDT Fri Nov 02 2018 000 WTPZ45 KNHC 030233 TCDEP5 Tropical Storm Xavier Discussion Number 2 NWS National Hurricane Center Miami FL EP252018 900 PM MDT Fri Nov 02 2018 For the 22nd time this year, a tropical storm (Xavier) has formed over the eastern North Pacific. The most recent intensity estimates from TAFB and the UW-CIMSS SATCON support increasing the initial intensity to 35 kt. Xavier is the first tropical storm to reach the "X" name on the East Pacific namelist since 1992. No changes of note were made to the intensity forecast. The tropical storm is strongly sheared from the southwest and convective activity is limited to the eastern semicircle of the cyclone. Although Xavier should be located over warm waters for the next 5 days, strong upper-level southwesterly flow will cause high wind shear across the cyclone. The HWRF, HMON, and COAMPS-TC models all forecast that the tropical storm could strengthen a little more over the next day or so, while the statistical guidance indicates that Xavier is already near its peak intensity. The NHC intensity forecast follows the consensus and shows slight strengthening through the weekend. By early next week, increased shear and a drier surrounding environment will likely cause Xavier to weaken and become a remnant low. It has been difficult to identify the center of Xavier this evening, but it is estimated that the tropical storm is still moving generally east-northeastward at around 7 kt. A weakness in the subtropical ridge created by a large deep-layer trough extending over central Mexico and the Gulf of Mexico should cause Xavier to turn toward the northeast or north overnight and tomorrow. There has been a shift in the GFS and its associated regional models, which now show a farther northeast track of Xavier, closer to the coast of Mexico. However, a majority of the dynamical models still show the cyclone turning abruptly westward and away from land while it weakens by early next week. Out of respect for the ECMWF and its ensemble, which show a much farther west track for Xavier, the NHC forecast has been nudged only slightly toward the northeast through 48 h and now lies a little to the west of the TVCE track consensus. FORECAST POSITIONS AND MAX WINDS INIT 03/0300Z 14.5N 108.2W 35 KT 40 MPH 12H 03/1200Z 14.8N 107.5W 40 KT 45 MPH 24H 04/0000Z 15.6N 106.8W 45 KT 50 MPH 36H 04/1200Z 16.4N 106.5W 45 KT 50 MPH 48H 05/0000Z 17.1N 106.4W 45 KT 50 MPH 72H 06/0000Z 17.8N 107.0W 35 KT 40 MPH 96H 07/0000Z 17.5N 109.0W 30 KT 35 MPH 120H 08/0000Z 18.0N 111.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Zelinsky

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