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Tropical Depression Eighteen-E Forecast Discussion Number 2

2018-09-08 22:51:09| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Sat Sep 08 2018 130 WTPZ43 KNHC 082051 TCDEP3 Tropical Depression Eighteen-E Discussion Number 2 NWS National Hurricane Center Miami FL EP182018 200 PM PDT Sat Sep 08 2018 GOES-16 visible imagery shows the center of the depression on the edge of a convective mass, with a large part of the eastern part of the circulation exposed due to shear. Dvorak estimates are a little higher than the last advisory, but the evidence is not strong enough yet to upgrade the system to a tropical storm, so the winds will stay 30 kt. Gradual strengthening is anticipated while the cyclone remains over warm waters within a light-to-moderate shear environment. After 72 hours, the water temperatures drop off quite a bit and weakening should begin. The biggest change is that the model guidance is considerably lower in this cycle, perhaps due to easterly shear persisting for a bit longer. Only a small decrease was made to the intensity forecast at long range, but later advisories could be lower if model trends continue. Visible imagery also helped reposition the depression about a degree west of the last advisory. Ironically, the initial motion estimate is unchanged, still 290/10 kt. A mid-level ridge over Mexico should steer the system northwestward for the next day or so, then the dominant eastern Pacific subtropical ridge is forecast to turn the system back toward the west-northwest. Numerical guidance is a fair distance west of the previous cycle, and the NHC forecast follows that trend, resulting in a large westward adjustment to the NHC forecast after absorbing the initial position change. FORECAST POSITIONS AND MAX WINDS INIT 08/2100Z 15.8N 116.8W 30 KT 35 MPH 12H 09/0600Z 16.5N 117.8W 35 KT 40 MPH 24H 09/1800Z 17.6N 118.8W 40 KT 45 MPH 36H 10/0600Z 18.9N 119.9W 45 KT 50 MPH 48H 10/1800Z 19.9N 121.3W 50 KT 60 MPH 72H 11/1800Z 21.0N 125.0W 60 KT 70 MPH 96H 12/1800Z 22.3N 129.0W 50 KT 60 MPH 120H 13/1800Z 23.5N 132.0W 35 KT 40 MPH $$ Forecaster Blake

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Hurricane Olivia Forecast Discussion Number 33

2018-09-08 22:50:07| Tropical Depression LIDIA

Issued at 200 PM PDT Sat Sep 08 2018

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Tropical Storm Isaac Forecast Discussion Number 5

2018-09-08 22:48:39| National Hurricane Center (Atlantic)

Issued at 500 PM AST Sat Sep 08 2018 510 WTNT44 KNHC 082048 TCDAT4 Tropical Storm Isaac Discussion Number 5 NWS National Hurricane Center Miami FL AL092018 500 PM AST Sat Sep 08 2018 The structure of the cyclone, while still a shear pattern, is improving, with the low-level center now near the convective overcast and improved outflow in the eastern semicircle. Satellite intensity estimates have increased to the 30-45 kt range, with the CIMSS satellite consensus technique now suggesting winds near 35 kt. Based on these estimates, the initial intensity is increased to 35 kt and the depression is upgraded to Tropical Storm Isaac. Isaac is now moving slowly westward, with the initial motion 275/6. The subtropical ridge to the north of Isaac is forecast to steer the system westward with an increasing forward speed for at least the next 2-3 days. After that time, there is some uncertainty in the track forecast due to the formation of a mid- to upper-level trough over the central Atlantic, with some of the track guidance showing a decrease in forward speed and a more northerly motion near the end of the forecast period. The GFS and ECMWF models show a continued westerly motion through that time, and the official forecast follows that scenario, although with a slower forward speed than in the previous forecast. The new forecast is again similar to the earlier forecast and lies near the various consensus models. Conditions appear favorable for gradual strengthening during the next 72 h as Isaac moves westward across the warm waters of the tropical Atlantic. In best agreement with the SHIPS model for the next three days, the new intensity forecast is raised from the previous forecast during this time. From 72-120 h, the system is expected to encounter westerly wind shear, which is expected to cause some weakening. FORECAST POSITIONS AND MAX WINDS INIT 08/2100Z 14.5N 36.6W 35 KT 40 MPH 12H 09/0600Z 14.6N 37.7W 40 KT 45 MPH 24H 09/1800Z 14.7N 39.5W 50 KT 60 MPH 36H 10/0600Z 14.7N 42.0W 60 KT 70 MPH 48H 10/1800Z 14.7N 44.6W 65 KT 75 MPH 72H 11/1800Z 14.5N 50.0W 75 KT 85 MPH 96H 12/1800Z 14.5N 55.5W 75 KT 85 MPH 120H 13/1800Z 15.0N 61.0W 70 KT 80 MPH $$ Forecaster Beven

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Tropical Storm Florence Forecast Discussion Number 38

2018-09-08 22:45:07| National Hurricane Center (Atlantic)

Issued at 500 PM AST Sat Sep 08 2018 748 WTNT41 KNHC 082045 TCDAT1 Tropical Storm Florence Discussion Number 38 NWS National Hurricane Center Miami FL AL062018 500 PM AST Sat Sep 08 2018 A NOAA P3 aircraft conducted a research mission several hours ago in Florence and measured SFMR surface winds of around 60 kt and winds up to 65 kt at a flight level of 8000 feet. Velocities of 65-70 kt at 500 meters were also measured by the Doppler radar on the plane. Based on these data, the initial wind speed is raised to 60 kt. Dropsonde data also showed that the central pressure was down to 989 mb. Florence is slowly recovering from the dry air its circulation ingested while it was under the influence of strong shear. Convection in the outer bands is relatively thin but is deeper and more persistent near the center. Now that the shear has decreased and the warm waters ahead of Florence reach deeper into the ocean, continued strengthening is anticipated. In fact, the official forecast continues to show a period of rapid intensification, now beginning 12-24 hours, with Florence reaching major hurricane intensity between 36-48 hours. One fly in the ointment is that the SHIPS diagnostics are keeping mid-level relative humidities around the cyclone around 50 percent, which isn't particularly moist, but I'm going to assume that Florence will be able to scour out the dry air within its circulation in the coming days. The HCCA model and the ICON intensity consensus support maintaining a forecast peak intensity of 125 kt in 4 days or so, so no significant changes were made from the previous forecast. Regardless of the specifics of the other models--some of which are higher and some of which are lower--Florence is expected to be a powerful major hurricane on days 3 through 5 as it moves across the southwestern Atlantic Ocean. Florence is creeping westward (270 degrees) at 4 kt, trapped between high pressure to its northeast and southwest. A different blocking ridge is expected to develop north and northeast of Bermuda over the next few days, causing Florence to accelerate toward the west-northwest and northwest between days 3-5. There have been some notable shifts in the model guidance on this cycle, with the ECMWF model swinging to the northeast closer to the GFS, and the HWRF model swinging farther south along the southern edge of the guidance envelope. Despite this change in the deterministic ECMWF run, its individual ensemble members are still showing a significant spread of solutions from just north of the Bahamas to offshore the coast of North Carolina by day 5. Because of this spread, the updated NHC track forecast largely maintains continuity and remains close to the TVCN multi-model consensus. And despite the ECMWF's shift, this track prediction remains north of the HCCA and FSSE solutions. Key Messages: 1. Florence is forecast to be a dangerous major hurricane near the southeast U.S. coast by late next week, and the risk of direct impacts continues to increase. However, given the uncertainty in track and intensity forecasts at those time ranges, it's too soon to determine the exact timing, location, and magnitude of those impacts. 2. Interests along the U.S. East Coast, particularly from north Florida through North Carolina, should closely monitor the progress of Florence, ensure they have their hurricane plan in place, and follow any advice given by local officials. 3. Large swells affecting Bermuda and portions of the U.S. East Coast will continue into next week. These swells will result in life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 08/2100Z 24.6N 54.7W 60 KT 70 MPH 12H 09/0600Z 24.6N 55.4W 70 KT 80 MPH 24H 09/1800Z 24.7N 56.6W 80 KT 90 MPH 36H 10/0600Z 25.0N 58.3W 95 KT 110 MPH 48H 10/1800Z 25.4N 60.5W 110 KT 125 MPH 72H 11/1800Z 26.9N 66.4W 120 KT 140 MPH 96H 12/1800Z 29.5N 72.5W 125 KT 145 MPH 120H 13/1800Z 32.5N 77.0W 120 KT 140 MPH $$ Forecaster Berg

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Hurricane Olivia Forecast Discussion Number 32

2018-09-08 16:59:37| Tropical Depression LIDIA

Issued at 800 AM PDT Sat Sep 08 2018

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