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Tropical Storm Xavier Forecast Discussion Number 12

2018-11-05 15:32:33| National Hurricane Center (East Pacific)

Issued at 800 AM MST Mon Nov 05 2018 000 WTPZ45 KNHC 051432 TCDEP5 Tropical Storm Xavier Discussion Number 12 NWS National Hurricane Center Miami FL EP252018 800 AM MST Mon Nov 05 2018 A burst of deep convection occurred over the low-level center around the time of the last advisory, but that activity has again been scoured off to the northeast due to 30 kt of southwesterly shear. Satellite intensity estimates have not changed, and the initial intensity remains 50 kt, which is very close to the latest UW-CIMSS ADT and SATCON estimates. Xavier has been tenaciously resisting the ill effects of shear for the time being. However, the circulation will be moving westward toward a drier environment where mid-level relative humidity values are 30-40 percent. In theory, the combination of strong shear and drier air should put an end to deep convection production, but relatively warm waters could still allow the cyclone to produce intermittent bursts of shower and thunderstorm activity over the next several days. Based on the latest intensity guidance, no changes were made to the official forecast, which continues to show Xavier becoming a remnant low in 48 hours and dissipating by day 4. Caught within a break in the subtropical ridge, Xavier is only creeping west-northwestward, or 295/3 kt. As deep convection gradually dwindles near the cyclone, the shallower circulation is expected to be steered westward to the south of a low-level ridge stretching across northern Mexico and the Baja California peninsula. The new NHC track forecast is nearly identical to the previous one during the first 24 hours. After 24 hours, it has been nudged southward toward the various consensus aids, continuing the trend that was noted by the previous forecaster. Even though Xavier is slowly moving away from the coast of Mexico, inclement weather is still occurring near the coasts of Colima and Jalisco, and tropical-storm-force winds could still be occurring in that vicinity. Therefore, it's prudent to continue the Tropical Storm Warning until we have confirmation that the strong winds have shifted farther offshore. FORECAST POSITIONS AND MAX WINDS INIT 05/1500Z 18.5N 106.2W 50 KT 60 MPH 12H 06/0000Z 18.7N 107.0W 40 KT 45 MPH 24H 06/1200Z 18.9N 108.3W 35 KT 40 MPH 36H 07/0000Z 18.9N 109.7W 30 KT 35 MPH 48H 07/1200Z 18.8N 111.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 08/1200Z 18.5N 113.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 09/1200Z...DISSIPATED $$ Forecaster Berg

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Tropical Storm Xavier Forecast Discussion Number 11

2018-11-05 09:42:00| National Hurricane Center (East Pacific)

Issued at 300 AM CST Mon Nov 05 2018 000 WTPZ45 KNHC 050841 TCDEP5 Tropical Storm Xavier Discussion Number 11 NWS National Hurricane Center Miami FL EP252018 300 AM CST Mon Nov 05 2018 The satellite presentation of Xavier has degraded somewhat overnight, with the main area of convection decreasing in coverage and becoming more separated from the low-level center. Somewhat surprisingly, a couple of ASCAT passes between 0345 and 0500 UTC indicated peak winds of around 50 kt. This suggests that Xavier may have been slightly stronger than previously estimated since the overall structure of the storm was better defined yesterday afternoon and evening. Based on these data, the intensity was adjusted to 50 kt on the 0600 UTC intermediate advisory, and remains at that value for now. The intensity forecast reasoning remains unchanged. Strong shear and an increasingly drier mid-level air mass are expected to cause the tropical storm to weaken fairly quickly over the next day or so, and the global models suggest that Xavier will degenerate into a remnant low in 36 to 48 hours. Xavier has been moving slowly northwestward or 305/3 kt. A low- to mid-level ridge that is building to the north of Xavier should cause the cyclone to turn west-northwestward, and then westward during the next 12 to 24 hours. As the system weakens it is forecast to move westward or west-southwestward within the low-level flow until dissipation occurs in 3 to 4 days. The track guidance envelope shifted somewhat southward this cycle, and as a result, the official forecast was adjusted in that direction but it remains to the north of the consensus models out of respect for continuity with the previous NHC track. FORECAST POSITIONS AND MAX WINDS INIT 05/0900Z 18.4N 105.9W 50 KT 60 MPH 12H 05/1800Z 18.7N 106.8W 40 KT 45 MPH 24H 06/0600Z 18.9N 108.0W 35 KT 40 MPH 36H 06/1800Z 19.1N 109.3W 30 KT 35 MPH 48H 07/0600Z 19.2N 110.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 08/0600Z 19.0N 112.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 09/0600Z...DISSIPATED $$ Forecaster Brown

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Tropical Storm Xavier Forecast Discussion Number 10

2018-11-05 03:35:02| National Hurricane Center (East Pacific)

Issued at 900 PM CST Sun Nov 04 2018 000 WTPZ45 KNHC 050234 TCDEP5 Tropical Storm Xavier Discussion Number 10 NWS National Hurricane Center Miami FL EP252018 900 PM CST Sun Nov 04 2018 Xavier continues to be influenced by strong southwesterly shear, on the order of 30 kt, yet appears to be maintaining its intensity for now. In fact, microwave imagery shows only a slight eastward tilt of the center with height which is surprising for a tropical cyclone apparently experiencing shear of such magnitude. It is quite possible that strong upper-level divergence over the area is helping to maintain the strength of the storm. Dvorak intensity estimates remain at 45 kt from both TAFB and SAB which will continue to be used for the advisory intensity. In spite of Xavier's resilience to a hostile atmospheric environment, the strong shear and an increasingly drier mid-level air mass should soon take their toll on the cyclone. The GFS and the ECMWF global models suggest that the system will degenerate into a remnant low within a couple of days, and this is also shown by the official forecast. Xavier has been moving slowly and just to the west of north, or a motion of 350/5 kt, toward a slight weakness in the mid-level flow to the southeast of the Baja California peninsula. A ridge is forecast to build to the north of the cyclone, and this should cause Xavier to turn toward the west-northwest during the next day or so. By 3-4 days, the weak and shallow cyclone is likely to move generally westward within the low-level flow field. The official forecast is similar to the previous one and is very close to the latest dynamical model consensus track. FORECAST POSITIONS AND MAX WINDS INIT 05/0300Z 18.5N 105.7W 45 KT 50 MPH 12H 05/1200Z 18.8N 106.4W 40 KT 45 MPH 24H 06/0000Z 19.3N 107.5W 35 KT 40 MPH 36H 06/1200Z 19.6N 108.7W 30 KT 35 MPH 48H 07/0000Z 19.8N 109.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 08/0000Z 19.7N 112.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 09/0000Z 19.5N 113.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 120H 10/0000Z...DISSIPATED $$ Forecaster Pasch

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Tropical Storm Xavier Forecast Discussion Number 9

2018-11-04 21:40:32| National Hurricane Center (East Pacific)

Issued at 300 PM CST Sun Nov 04 2018 000 WTPZ45 KNHC 042040 TCDEP5 Tropical Storm Xavier Discussion Number 9 NWS National Hurricane Center Miami FL EP252018 300 PM CST Sun Nov 04 2018 After being sheared off this morning, deep convection has redeveloped and persisted over Xavier's center of circulation. Dvorak Current Intensity numbers from TAFB and SAB remain 3.0, and the latest UW-CIMSS SATCON estimate is 43 kt. The initial intensity therefore remains 45 kt. Although shear analyses indicate that about 25 kt of southwesterly shear is affecting Xavier, an upper-level trough in the vicinity appears to be producing a decent amount of divergence aloft to support the ongoing convection. The global models show that trough dissipating and the upper flow becoming unidirectional within 12 hours, which should cut off the divergence and allow the adverse effects of shear and dry air to take over. As a result, gradual weakening is expected during the next couple of days, and Xavier may cease to produce organized deep convection (and thus become a remnant low) in 36-48 hours. The remnant low should dissipate by day 4, if not sooner. The updated NHC intensity forecast is conservative, following continuity from the previous forecast and lying near the upper bound of the intensity models. Xavier's motion still appears to be slowly northward, or 350/5 kt. The global models, most of which assume that Xavier will become a shallow system soon, show the cyclone turning northwestward and west-northwestward during the next 24 hours. While this seems reasonable, as long as Xavier maintains vertical integrity, it will likely continue moving closer to the right side of the guidance envelope. With the assumption that deep convection won't dissipate right away, the NHC track forecast is to the right of the consensus aids, close to the ECMWF solution, during the first 24 hours. After 24 hours, it remains close to the TVCN multi-model consensus. A 1600 UTC ASCAT pass indicated that Xavier's tropical-storm-force wind field on the east side was larger than previously estimated, with those winds lying near the coast of southwestern Mexico. As a result, the government of Mexico issued a Tropical Storm Warning for a portion of the coasts of Michoacan, Colima, and Jalisco. Locally heavy rainfall and large swells are also likely to affect the coast of southwestern Mexico during the next day or two. FORECAST POSITIONS AND MAX WINDS INIT 04/2100Z 18.1N 105.5W 45 KT 50 MPH 12H 05/0600Z 18.7N 106.0W 40 KT 45 MPH 24H 05/1800Z 19.2N 107.1W 35 KT 40 MPH 36H 06/0600Z 19.5N 108.2W 30 KT 35 MPH 48H 06/1800Z 19.6N 109.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 07/1800Z 19.4N 111.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 08/1800Z 19.0N 114.0W 15 KT 15 MPH...POST-TROP/REMNT LOW 120H 09/1800Z...DISSIPATED $$ Forecaster Berg

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Tropical Storm Xavier Forecast Discussion Number 7

2018-11-04 09:38:29| National Hurricane Center (East Pacific)

Issued at 300 AM CST Sun Nov 04 2018 000 WTPZ45 KNHC 040838 TCDEP5 Tropical Storm Xavier Discussion Number 7 NWS National Hurricane Center Miami FL EP252018 300 AM CST Sun Nov 04 2018 Xavier remains a sheared tropical cyclone. Although deep convection continues to develop over the northeastern portion of the circulation, recent satellite imagery suggests that the center has become a little more exposed to the southwest of the convective mass. Objective and subjective Dvorak T-numbers have not changed overnight, and a blend of those data along with the latest SATCON estimate still yields an initial wind speed of 50 kt. Xavier has likely peaked in intensity as the strong vertical wind shear over the system is forecast to increase further today and tonight. This should result in gradual weakening during the next day or two, and the new NHC intensity forecast follows the trend of the latest multi-model intensity consensus. The dynamical models indicate that Xavier will lose its deep convection in 48 to 72 hours, and the official forecast calls for the system to degenerate to a remnant low by day 3. The latest satellite fixes suggest that Xavier has made its anticipated northward turn. The tropical storm is forecast to move slowly northward today, but it should turn west-northwestward, then westward during the next 24 to 36 hours as it weakens and is steered by the low-level flow to the south of a subtropical ridge. The UKMET model remains an outlier as it keeps the cyclone stronger and deeper which allows Xavier to move much farther north. The remainder of the track guidance is in good agreement, and the updated NHC track is near a blend of the HWRF, GFS, and ECMWF models, and is very close to the latest FSSE guidance. Although the center Xavier is not forecast to move much closer to the coast of southwestern Mexico, large swells and locally heavy rainfall could affect portions of that area during the next day or two. FORECAST POSITIONS AND MAX WINDS INIT 04/0900Z 16.6N 105.9W 50 KT 60 MPH 12H 04/1800Z 17.3N 105.9W 45 KT 50 MPH 24H 05/0600Z 17.8N 106.7W 40 KT 45 MPH 36H 05/1800Z 18.0N 107.8W 35 KT 40 MPH 48H 06/0600Z 18.2N 109.0W 30 KT 35 MPH 72H 07/0600Z 18.3N 111.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 08/0600Z 18.5N 113.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 09/0600Z...DISSIPATED $$ Forecaster Brown

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