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Tropical Storm Rosa Forecast Discussion Number 24

2018-10-01 04:34:08| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Sun Sep 30 2018 547 WTPZ45 KNHC 010234 TCDEP5 Tropical Storm Rosa Discussion Number 24 NWS National Hurricane Center Miami FL EP202018 800 PM PDT Sun Sep 30 2018 All of Rosa's associated deep convection is located within the northeastern quadrant of the circulation, moving out ahead of the center due to 25-30 kt of southwesterly shear. Subjective and objective intensity estimates have decreased since the previous advisory but encompass a wide range from about 45 kt to 65 kt. The initial intensity is lowered to 55 kt, the average of these estimates and similar to the latest UW-CIMSS SATCON estimate. Rosa's center is now over sub-24C waters, heading for waters around 21C along the Baja California coast, and the shear is forecast to increase further in the coming days. As a result, Rosa is expected to weaken below tropical storm intensity between 24-36 hours, after it has reached the Baja California coast. All of the cyclone's deep convection is likely to be sheared away soon thereafter, making Rosa a remnant low between 36-48 hours, if not sooner. The remnant low should dissipate over Arizona by 48 hours. Rosa continues to move north-northeastward, or 025/10 kt. The flow on the eastern side of a large mid-level trough located off the U.S. West Coast should continue to steer Rosa north-northeastward, with some acceleration beginning by Monday night. Although there are still some speed differences among the models, particularly between the faster GFS and slower ECMWF, the guidance remains tightly clustered overall, and the new NHC track forecast is very close to the multi-model consensus aids. Key Messages: 1. The main hazard expected from Rosa or its remnants is very heavy rainfall in Baja California, northwestern Sonora, and the U.S. Desert Southwest. These rains are expected to produce life-threatening flash flooding and debris flows in the deserts, and landslides in mountainous terrain. For more information about potential rainfall in that area, please see products from the Weather Prediction Center and your local NWS forecast office. 2. Tropical storm conditions are expected over portions of the central and northern Baja California peninsula on Monday, possibly spreading to the northern Gulf of California Monday night. Interests in those locations should monitor the progress of Rosa. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 26.0N 117.6W 55 KT 65 MPH 12H 01/1200Z 27.3N 116.8W 45 KT 50 MPH 24H 02/0000Z 29.1N 115.6W 35 KT 40 MPH 36H 02/1200Z 31.5N 114.1W 30 KT 35 MPH...NEAR THE SONORA COAST 48H 03/0000Z 34.2N 112.4W 25 KT 30 MPH...POST-TROP/INLAND 72H 04/0000Z...DISSIPATED $$ Forecaster Berg

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Tropical Storm Leslie Forecast Discussion Number 18

2018-09-30 22:38:34| National Hurricane Center (Atlantic)

Issued at 500 PM AST Sun Sep 30 2018 762 WTNT43 KNHC 302038 TCDAT3 Tropical Storm Leslie Discussion Number 18 NWS National Hurricane Center Miami FL AL132018 500 PM AST Sun Sep 30 2018 Leslie has generally changed little in organization today. The tropical storm continues to produce deep convection in a band to the southeast of the center, but there is a minimal amount of shower activity elsewhere. This asymmetric cloud pattern is due to about 25 kt of northwesterly wind shear. The initial intensity is again held at 45 kt, but some of the satellite estimates suggest that this could be a little generous. The global models show the upper-level pattern becoming more favorable over Leslie in about a day, which combined with warmer SSTs should allow Leslie to gradually strengthen during the next 2 to 3 days. After that time, the storm is expected to move northeastward back over its previous track and cooler waters partly caused by its own upwelling. These conditions should end the strengthening trend and induce some weakening. The NHC intensity forecast is largely an update of the previous one and in line with the IVCN, FSSE, and HCCA consensus models. Leslie is drifting to the southwest, with the latest initial motion estimate being 240/4 kt. The storm is forecast to remain in very weak steering currents, and Leslie will likely drift southward to southwestward during the next few days on the east side of a mid-level ridge. Thereafter, a developing trough to the southwest of Leslie should cause the system to move northeastward at a slightly faster pace. The models continue to shift back and forth each cycle, which is not surprising given the weak steering. This forecast is adjusted a little to the left of the previous one to come into better agreement with the latest models. The bottom line is that Leslie is forecast to meander over the central Atlantic for the next several days. Large swells generated by Leslie when it was a strong extratropical low will continue to affect the east coast of the United States and most of the Greater and Lesser Antilles for another day or two. These swells could cause life-threatening surf and rip currents. Although the swells will diminish some by mid-week, they will likely remain hazardous for the same locations through the forecast period due to Leslie's slow motion. FORECAST POSITIONS AND MAX WINDS INIT 30/2100Z 33.5N 53.2W 45 KT 50 MPH 12H 01/0600Z 33.3N 53.7W 50 KT 60 MPH 24H 01/1800Z 32.9N 54.3W 55 KT 65 MPH 36H 02/0600Z 32.1N 55.0W 60 KT 70 MPH 48H 02/1800Z 31.3N 55.3W 65 KT 75 MPH 72H 03/1800Z 31.0N 54.7W 65 KT 75 MPH 96H 04/1800Z 33.5N 53.5W 60 KT 70 MPH 120H 05/1800Z 36.5N 52.0W 60 KT 70 MPH $$ Forecaster Cangialosi

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Tropical Storm Sergio Forecast Discussion Number 6

2018-09-30 22:35:33| National Hurricane Center (East Pacific)

Issued at 300 PM MDT Sun Sep 30 2018 110 WTPZ41 KNHC 302035 TCDEP1 Tropical Storm Sergio Discussion Number 6 NWS National Hurricane Center Miami FL EP212018 300 PM MDT Sun Sep 30 2018 Satellite imagery over the past several hours as well as microwave and scatterometer data indicate that the center of Sergio is farther south than previously analyzed. The deep convection near the center has become ragged in appearance and elongated from east-west. However, microwave data continues to show a well-defined mid-level circulation, and satellite intensity estimates are unanimously supporting 55 kt, which will be the initial intensity for this advisory. The initial motion estimate is now 260/11 kt, partially due to adjustment of the center farther south. Otherwise, there are no changes in the forecast track philosophy from the previous advisory. For the next couple of days, Sergio should move generally westward or just south of due west around the southern periphery of a large deep-layer subtropical ridge extending from Mexico westward across the eastern Pacific. By 48 hours, a mid- to upper-level trough moving southeastward along and offshore of the western U.S. will erode the western part of the ridge. This will allow the cyclone to turn west-northwestward to northwestward from 48- to 96-hours with a gradual decrease in forward speed. Very near the end of the forecast period, the trough should shift eastward and low- to mid-level ridging should build to the northwest of the cyclone. This pattern change should induce a more westward turn by 120 hours. Despite the current ragged appearance of the cyclone, the environment of low-shear, high-moisture, and warm waters are expected to support a period of rapid intensification sometime within the next 36 hours or so. By 36 hours, northeasterly shear is expected to develop over the storm and increase to 25 kt by 48 hours. This should at least limit the rate of intensification if not weaken the cyclone slightly from 48- to 72-hours. After that time, global models indicate that the shear will lessen to under 10 kt for the remainder of the forecast period. There may be a window of time beginning after 72 hours where some additional strengthening could occur. By 96 hours, the system will then be moving over waters of 26-27 C very near a gradient of cooler SSTs just to the north. The current intensity forecast calls for a steadying of intensity after the shear abates, then a slow weakening trend commences by the end of the period due to cooler SSTs. Other than a slight delay in Sergio becoming a hurricane, the intensity forecast is essentially the same as the previous forecast and remains close to the dynamical model consensus. Based on this intensity forecast, Sergio is still forecast to become a major hurricane on Tuesday. FORECAST POSITIONS AND MAX WINDS INIT 30/2100Z 11.5N 106.3W 55 KT 65 MPH 12H 01/0600Z 11.4N 108.1W 65 KT 75 MPH 24H 01/1800Z 11.2N 110.4W 80 KT 90 MPH 36H 02/0600Z 11.4N 112.6W 95 KT 110 MPH 48H 02/1800Z 11.9N 114.5W 105 KT 120 MPH 72H 03/1800Z 13.8N 117.5W 100 KT 115 MPH 96H 04/1800Z 16.0N 120.0W 100 KT 115 MPH 120H 05/1800Z 17.3N 122.0W 90 KT 105 MPH $$ Forecaster Latto/Cangialosi

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Hurricane Rosa Forecast Discussion Number 23

2018-09-30 22:33:34| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Sun Sep 30 2018 534 WTPZ45 KNHC 302033 TCDEP5 Hurricane Rosa Discussion Number 23 NWS National Hurricane Center Miami FL EP202018 200 PM PDT Sun Sep 30 2018 An Air Force Reserve Unit Hurricane Hunter aircraft recently investigated Rosa, and found peak 700-mb flight-level winds that still supported minimal hurricane intensity. However, the SFMR-observed surface winds were somewhat lower, which is not surprising since the system has minimal deep convection and is over 24-25 deg SSTs. Given that the central pressure is still fairly low, 982 mb, Rosa is being maintained, perhaps generously, as a hurricane for this advisory. With increasing shear and cooler waters ahead for the system, weakening seems inevitable. The official intensity forecast is similar to the latest HWRF model prediction, and shows Rosa weakening to a depression by the time it reaches the southwest United States. The initial motion is north-northeastward, or 025/10 kt. The track forecast scenario remains essentially unchanged from the previous couple of advisory packages. The flow on the eastern side of a large mid-level trough approaching from the west should steer Rosa on a north-northeastward track for the next couple of days. The official track forecast is very close to the latest dynamical model consensus. The wind radii have been adjusted slightly based on data from a recent ASCAT scatterometer overpass. Key Messages: 1. The main hazard expected from Rosa or its remnants is very heavy rainfall in Baja California, northwestern Sonora, and the U.S. Desert Southwest. These rains are expected to produce life-threatening flash flooding and debris flows in the deserts, and landslides in mountainous terrain. For more information about potential rainfall in that area, please see products from the Weather Prediction Center and your local NWS forecast office. 2. Tropical storm conditions are expected over portions of the central and northern Baja California peninsula on Monday, possibly spreading to the northern Gulf of California Monday night. Interests in those locations should monitor the progress of Rosa. FORECAST POSITIONS AND MAX WINDS INIT 30/2100Z 25.2N 118.1W 65 KT 75 MPH 12H 01/0600Z 26.5N 117.4W 55 KT 65 MPH 24H 01/1800Z 28.1N 116.2W 45 KT 50 MPH 36H 02/0600Z 29.9N 115.0W 40 KT 45 MPH...INLAND 48H 02/1800Z 32.3N 113.9W 30 KT 35 MPH...INLAND 72H 03/1800Z 37.0N 112.0W 20 KT 25 MPH...POST-TROP/INLAND 96H 04/1800Z...DISSIPATED $$ Forecaster Pasch

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Tropical Storm Sergio Forecast Discussion Number 5

2018-09-30 16:58:05| National Hurricane Center (East Pacific)

Issued at 1000 AM CDT Sun Sep 30 2018 200 WTPZ41 KNHC 301457 TCDEP1 Tropical Storm Sergio Discussion Number 5 NWS National Hurricane Center Miami FL EP212018 1000 AM CDT Sun Sep 30 2018 Recent microwave data indicate that the inner core of Sergio continues to become better defined, with an eye-like feature evident. However, this eye feature is not yet apparent in geostationary satellite imagery. Deep convection with cloud top temperatures of -70 C are concentrated around the storm's center as well as along a prominent banding feature on the south side. The average of available satellite intensity estimates support an intensity of 50 kt, which will be the initial intensity for this advisory. The initial motion estimate is 270/11 kt. There continues to be no significant changes in the forecast track philosophy from the previous few forecasts. For the next couple of days, Sergio should move generally westward or just south of due west around the southern periphery of a large deep-layer subtropical ridge that extends from Mexico westward across the eastern Pacific. By 48 hours, a mid- to upper-level trough will move southeastward along and offshore the western U.S., which will erode the ridge from the west. This will allow the cyclone to turn west-northwestward then northwestward from 48- to 96-hours with a gradual decrease in forward speed. Thereafter, the trough should shift eastward and low- to mid-level ridging should build to the northwest of the cyclone. This pattern change should induce a more westward turn toward the end of the forecast period. Sergio will remain in an environment of low-shear, high-moisture, and over warm waters for the next 24 hours or so, which should result in rapid intensification. This is in agreement with rapid intensification indices from the SHIPS model of 40 to 45 percent over the next 24 hours. By 36 hours, northeasterly shear is expected to develop over the storm environment and increase to 25 kt by 48 hours. This should at least limit the rate of intensification if not weaken the cyclone slightly from 48- to 72-hours. After that time, global models indicate that the shear will lessen to under 10 kt by 96 hours, but by that time the system will be moving over waters of 26-27 C very near a gradient of cooler SSTs just to the north. Based on this, the intensity remains steady from 72- to 96-hours and then shows slow weakening by the end of the period. The intensity forecast is a little higher that the previous advisory, and is close to the dynamical model consensus. Based on this intensity forecast, Sergio is forecast to become a major hurricane by Tuesday. FORECAST POSITIONS AND MAX WINDS INIT 30/1500Z 12.1N 105.4W 50 KT 60 MPH 12H 01/0000Z 12.1N 107.0W 65 KT 75 MPH 24H 01/1200Z 11.8N 109.2W 80 KT 90 MPH 36H 02/0000Z 11.7N 111.4W 95 KT 110 MPH 48H 02/1200Z 12.0N 113.5W 105 KT 120 MPH 72H 03/1200Z 13.6N 116.6W 100 KT 115 MPH 96H 04/1200Z 16.0N 119.0W 100 KT 115 MPH 120H 05/1200Z 17.5N 121.5W 90 KT 105 MPH $$ Forecaster Latto/Cangialosi

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