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Hurricane Sergio Forecast Discussion Number 34

2018-10-07 22:33:42| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Sun Oct 07 2018 000 WTPZ41 KNHC 072033 TCDEP1 Hurricane Sergio Discussion Number 34 NWS National Hurricane Center Miami FL EP212018 200 PM PDT Sun Oct 07 2018 Sergio has maintained its annular-like structure over the past several hours. The eye has expanded to nearly 90 n mi across, and there is little evidence of convective banding in multiple microwave overpasses since 1200 UTC this morning. Dvorak classifications from TAFB and SAB have decreased since the last advisory, however the UW-CIMSS ADT and SATCON are a little higher, so the initial intensity has been lowered only slightly to 85 kt. Very little change has been made to the official track or intensity forecasts. Sergio is still forecast to slow down and turn northward over the next day or so. In fact, the 12 h forecast point is practically already inside the eye of the hurricane. By Tuesday, one or more shortwave troughs working southward along the western side of a deep-layer trough centered over the southwestern U.S. should cause Sergio to accelerate northeastward. Interestingly, although the various global models solutions have changed with this forecast cycle, the consensus has been fairly consistent, so only minor adjustments were required to the official track forecast. Slow weakening is still anticipated over the next few days as Sergio possibly maintains its annular structure. By mid-week, Sergio will be moving over progressively cooler waters, and a faster rate of weakening is likely. The NHC forecast is very similar to the previous advisory, and is near the IVCN and HCCA intensity consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 07/2100Z 14.7N 127.5W 85 KT 100 MPH 12H 08/0600Z 15.0N 128.1W 80 KT 90 MPH 24H 08/1800Z 15.6N 128.4W 75 KT 85 MPH 36H 09/0600Z 16.4N 127.9W 70 KT 80 MPH 48H 09/1800Z 17.3N 126.7W 65 KT 75 MPH 72H 10/1800Z 19.6N 122.8W 60 KT 70 MPH 96H 11/1800Z 23.5N 118.0W 50 KT 60 MPH 120H 12/1800Z 28.0N 112.5W 40 KT 45 MPH $$ Forecaster Zelinsky

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Tropical Depression Fourteen Forecast Discussion Number 4

2018-10-07 16:53:39| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Sun Oct 07 2018 000 WTNT44 KNHC 071453 TCDAT4 Tropical Depression Fourteen Discussion Number 4 NWS National Hurricane Center Miami FL AL142018 1000 AM CDT Sun Oct 07 2018 Satellite and radar data indicate that the depression continues to become better organized, but surface data suggests the circulation may be somewhat elongated. There is still evidence of westerly shear as the center is located near the western edge of the main convective mass, but there has been an increase in banding over the eastern semicircle since yesterday afternoon. The depression appears to be close to tropical storm strength and Dvorak estimates from TAFB and SAB are between 30-35 kt. An Air Force Reserve reconnaissance aircraft is scheduled to investigate the system early this afternoon and should provide a better assessment of the intensity of the cyclone. For now, the intensity is held at a possibly conservative 30 kt. The moderate westerly shear that is affecting the depression is forecast to gradually decrease over the next day or two as an upper-level trough over the Gulf of Mexico moves westward and weakens. This, in combination with warm waters, should allow for gradual strengthening as the system moves northward over the Gulf of Mexico. Nearly all of the intensity models bring the cyclone to hurricane strength over the Gulf of Mexico in 2 to 3 days, and the NHC forecast follows suit. The new NHC intensity forecast is slightly higher than the previous advisory and again lies near the ICON intensity consensus. This is a little below the more aggressive HWRF and HCCA models. The depression is moving northward at about 5 kt. The system is forecast to move generally northward during the next 2 to 3 days, with some increase in forward speed as it moves between a deep-layer ridge over the western Atlantic and a trough over the west-central United Sates. A northeastward turn is expected after 72 hours as the aforementioned trough progresses eastward across the central United States. The dynamical models generally agree on the overall scenario, but there are still large difference in forward speed. In fact, the ECMWF ensemble has members that are still over the Gulf of Mexico in 5 days, and others that reach southern New England in that time period. The NHC forecast is near the left side of the guidance envelope through 48 hours out of respect for the GFS and ECMWF that are both on that side of the track spread. After that time, the NHC track forecast is close to the various consensus aids to account for both the along and cross track spread of the guidance. Key Messages for Tropical Depression Fourteen: 1. The depression is forecast to produce heavy rainfall and flash flooding over portions of western Cuba and the northeastern Yucatan Peninsula of Mexico during the next couple of days. 2. The depression is forecast to become a tropical storm later today, and tropical storm conditions are expected by tonight over portions of western Cuba and the northeastern Yucatan Peninsula, where tropical storm warnings are in effect. 3. There is an increasing risk of dangerous storm surge, rainfall, and wind impacts over portions of the northern Gulf Coast by mid-week, although it is too soon to specify the exact location and magnitude of these impacts. Residents in these areas should monitor the progress of this system. FORECAST POSITIONS AND MAX WINDS INIT 07/1500Z 19.2N 86.9W 30 KT 35 MPH 12H 08/0000Z 20.0N 86.5W 40 KT 45 MPH 24H 08/1200Z 21.5N 86.5W 45 KT 50 MPH 36H 09/0000Z 23.2N 86.8W 55 KT 65 MPH 48H 09/1200Z 24.9N 87.2W 60 KT 70 MPH 72H 10/1200Z 28.7N 86.5W 70 KT 80 MPH 96H 11/1200Z 33.0N 82.5W 45 KT 50 MPH...INLAND 120H 12/1200Z 37.8N 73.0W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown

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Tropical Storm Leslie Forecast Discussion Number 45

2018-10-07 16:50:09| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Sun Oct 07 2018 000 WTNT43 KNHC 071449 TCDAT3 Tropical Storm Leslie Discussion Number 45 NWS National Hurricane Center Miami FL AL132018 1100 AM AST Sun Oct 07 2018 Despite marginal SSTs near 24 deg C, Leslie has persisted with little change in its structure. An average of the UW-CIMSS SATCON and current intensity estimates from TAFB and SAB still supports an initial intensity of 50 kt. Although Leslie is currently located in a low-shear environment, GFS and ECMWF SHIPS diagnostics suggests that mid-level humidities are fairly low, and the cyclone should remain over marginal SSTs for the foreseeable future. All of the intensity guidance forecasts little to no intensity change during the next day or so. However, by 36 h, nearly all of the dynamical models, both global and regional, forecast that Leslie will begin to restrengthen. On the other hand, the statistical-dynamical models do not forecast much change through day 5. The NHC forecast has been adjusted a little higher to keep it close to the intensity consensus, and I can't rule out that Leslie could become a hurricane again at some point during the coming week. No large changes were made to the NHC track forecast, but this should not be interpreted as a sign of confidence in the forecast. Leslie is currently moving with an initial motion of east-southeast, or 115/9 kt. The track model spread is high from the very beginning of the forecast, with the GFS and its associated regional models indicating that Leslie will continue on a similar heading for the next several days, while the ECMWF and UKMET forecast that Leslie will slow down and turn soon turn toward the southeast or south-southeast. The track forecast variance stems from differences in how quickly the models show Leslie separating from a mid-level trough to its north, if at all, and by day 5, the GFS and ECMWF solutions vary by about 750 n mi. At this point, I don't have a good reason to pick one solution over another, and it should be noted that based on the ECMWF ensemble tracks, there is a whole spectrum of possible solutions between these extremes. The NHC track forecast therefore remains near the TVCN and GFEX aids as a course of least regret, but significant changes could be required to future advisories if the track of Leslie becomes more clear. Large swells generated by Leslie are expected to continue through tonight across the northeastern coast of the United States, Bermuda, the Greater and Lesser Antilles, and Atlantic Canada. Please consult products from your local weather office as these conditions could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 07/1500Z 36.6N 51.4W 50 KT 60 MPH 12H 08/0000Z 36.2N 49.7W 50 KT 60 MPH 24H 08/1200Z 35.4N 47.3W 50 KT 60 MPH 36H 09/0000Z 34.2N 44.5W 55 KT 65 MPH 48H 09/1200Z 32.6N 41.7W 55 KT 65 MPH 72H 10/1200Z 29.1N 36.6W 60 KT 70 MPH 96H 11/1200Z 28.5N 31.9W 60 KT 70 MPH 120H 12/1200Z 30.0N 28.0W 55 KT 65 MPH $$ Forecaster Zelinsky

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Hurricane Sergio Forecast Discussion Number 33

2018-10-07 16:38:08| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Sun Oct 07 2018 000 WTPZ41 KNHC 071437 TCDEP1 Hurricane Sergio Discussion Number 33 NWS National Hurricane Center Miami FL EP212018 800 AM PDT Sun Oct 07 2018 Somewhat quickly and unexpectedly, Sergio took on the appearance of an annular hurricane overnight. The eye of the hurricane expanded, nearly doubling in size (now 70 n mi across), and most of the banding features disappeared. However, IR imagery over the past hour or two indicates that the hurricane is still somewhat asymmetrical, suggesting that the hurricane may not have a classical annular structure, at least not yet. The initial intensity has been lowered to 90 kt, in agreement with the latest current intensity estimates from TAFB and SAB. The hurricane continues to move due west with an initial forward speed of 7 kt. Sergio is still expected to slow down and turn first northward, and then northeastward over the next couple of days. By mid-week, a mid-level shortwave trough moving southward off coast of California should cause Sergio to accelerate northeastward toward the Baja California peninsula. The global models remain in fairly good agreement on the track of the cyclone through the middle of next week, and only small changes were made to the NHC track forecast to move it closer to the model consensus. As long as Sergio can maintain its annular-like structure, only slow weakening is anticipated due to continued effects of ocean upwelling combined with the slow forward motion of the hurricane. By the end of the forecast period, Sergio will be moving over much cooler SSTs located west of the Baja California peninsula, and a faster weakening rate is forecast. Given the lower initial intensity of Sergio, the official intensity forecast is a little lower for the first two days of the forecast, but is very similar beyond that time. FORECAST POSITIONS AND MAX WINDS INIT 07/1500Z 14.5N 126.8W 90 KT 105 MPH 12H 08/0000Z 14.8N 127.6W 85 KT 100 MPH 24H 08/1200Z 15.2N 128.2W 80 KT 90 MPH 36H 09/0000Z 15.9N 128.1W 75 KT 85 MPH 48H 09/1200Z 16.7N 127.3W 70 KT 80 MPH 72H 10/1200Z 18.8N 123.8W 65 KT 75 MPH 96H 11/1200Z 22.0N 119.5W 55 KT 65 MPH 120H 12/1200Z 26.5N 114.0W 45 KT 50 MPH $$ Forecaster Zelinsky

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Hurricane Sergio Forecast Discussion Number 32

2018-10-07 10:53:03| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Sun Oct 07 2018 000 WTPZ41 KNHC 070852 TCDEP1 Hurricane Sergio Discussion Number 32 NWS National Hurricane Center Miami FL EP212018 200 AM PDT Sun Oct 07 2018 Sergio appears to have lost some strength during the past several hours. Deep convection has decreased in intensity, and the eye appears larger and more ragged in recent satellite images. The initial intensity is lowered a little to 100 kt, which is near the upper end of the satellite intensity estimates, and this could be a little generous. The hurricane is still moving westward at about 7 kt, and a slow westward or west-northwestward motion is expected for the next 12 hours. The steering currents are expected to weaken later today, and Sergio will likely drift northwestward and northward tonight and Monday. After that time, a large trough over the southwestern United States is expected to cause Sergio to move toward the northeast with increasing forward speed. The track models are tightly clustered, and only small changes were made to the previous NHC forecast. The predicted slow motion of the tropical cyclone during the next couple of days will likely cause ocean upwelling, which could result in continued slow weakening in the short term. In the longer range, the models show Sergio moving into an atmospheric environment of drier air and stronger shear and over waters cooler than 26 deg C, which should continue the weakening trend or even accelerate it. The NHC intensity forecast is largely an update of the previous one, and it is in best agreement with the IVCN and HCCA models. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 14.6N 126.1W 100 KT 115 MPH 12H 07/1800Z 14.7N 127.0W 95 KT 110 MPH 24H 08/0600Z 15.0N 127.7W 90 KT 105 MPH 36H 08/1800Z 15.7N 127.8W 85 KT 100 MPH 48H 09/0600Z 16.5N 127.2W 80 KT 90 MPH 72H 10/0600Z 18.5N 124.3W 70 KT 80 MPH 96H 11/0600Z 22.0N 119.6W 60 KT 70 MPH 120H 12/0600Z 26.6N 114.2W 45 KT 50 MPH $$ Forecaster Cangialosi

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