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Tropical Storm Hilda Forecast Discussion Number 19

2021-08-04 10:47:35| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Wed Aug 04 2021 000 WTPZ43 KNHC 040847 TCDEP3 Tropical Storm Hilda Discussion Number 19 NWS National Hurricane Center Miami FL EP082021 200 AM PDT Wed Aug 04 2021 Hilda continues to weaken tonight. For a 12 h period, the low-level circulation was mostly devoid of deep convection, though recently a few convective cells are redeveloping south of the estimated center. Unfortunately, there has not been any recent scatterometer data to help determine the storm's intensity. The current initial intensity of Hilda is set to a possibly generous 40 kt for this advisory, blending the final-T numbers and current intensity estimates from TAFB and SAB, in addition to the most recent UW-CIMSS SATCON intensity estimate. Further weakening is forecast, as Hilda is now moving over sea-surface temperatures below 25 C, though some residual mid-level moisture may allow for sporadic convective bursts to occur for the next 24-36 hours. By 48 hours, the ECMWF, GFS, and HWRF models all agree Hilda will lose any remaining organized convection and become a remnant low, with this low opening up to a trough this weekend, well east-northeast of the Hawaiian Islands. Now that Hilda is becoming an increasingly shallow cyclone, the storm is beginning to bend slightly to the left, now moving to the west-northwest at 300/8 kt. Low- to mid-level ridging to the north and east of Hilda is expected to build in further over the next several days, and should allow the cyclone to turn a bit more westward at a slightly faster motion by the end of the forecast period. The latest NHC track forecast is very close to the previous one, and remains near the multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 04/0900Z 18.9N 126.6W 40 KT 45 MPH 12H 04/1800Z 19.6N 127.8W 35 KT 40 MPH 24H 05/0600Z 20.4N 129.5W 30 KT 35 MPH 36H 05/1800Z 21.3N 131.5W 30 KT 35 MPH 48H 06/0600Z 22.1N 133.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 06/1800Z 22.6N 136.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 07/0600Z...DISSIPATED $$ Forecaster Papin/Beven

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Post-Tropical Cyclone Ignacio Forecast Discussion Number 10

2021-08-04 04:36:54| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Tue Aug 03 2021 000 WTPZ45 KNHC 040236 TCDEP5 Post-Tropical Cyclone Ignacio Discussion Number 10 NWS National Hurricane Center Miami FL EP102021 800 PM PDT Tue Aug 03 2021 Ignacio consists of a swirl of low-level clouds and has been devoid of deep convection anywhere near its center since this morning. Therefore the system no longer qualifies as a tropical cyclone and is now a remnant low, or a post-tropical cyclone. The low has been moving east-southeastward, or about 120/6 kt. A turn toward the southeast and south is expected on Wednesday while the system moves around the northern side of a low-level ridge. Although the low will be moving over slightly warmer waters, strong easterly shear should prevent regeneration, and the system should dissipate in 24 h or so. This is the last advisory issued by the National Hurricane Center on Ignacio. For additional information on the remnant low please see High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFEPI, WMO header FZPN02 KWBC, and on the web at ocean.weather.gov/shtml/NFDHSFEPI.php FORECAST POSITIONS AND MAX WINDS INIT 04/0300Z 20.1N 115.0W 25 KT 30 MPH...POST-TROPICAL 12H 04/1200Z 19.6N 114.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 24H 05/0000Z...DISSIPATED $$ Forecaster Pasch

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Tropical Storm Hilda Forecast Discussion Number 18

2021-08-04 04:36:27| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Tue Aug 03 2021 000 WTPZ43 KNHC 040236 TCDEP3 Tropical Storm Hilda Discussion Number 18 NWS National Hurricane Center Miami FL EP082021 800 PM PDT Tue Aug 03 2021 Hilda is a weakening tropical cyclone. Its low-level center is now exposed in visible satellite imagery, and infrared cloud top temperatures have rapidly warmed as the system is currently not producing any deep convection. Despite this lack of convection, earlier scatterometer data revealed several 45-kt wind vectors in the northern and eastern portions of the circulation. The initial intensity is lowered to 45 kt for this advisory, which is supported by a blend of the final-T numbers and current intensity estimates from TAFB and SAB, and the objective UW-CIMSS SATCON estimate. A mid-level ridge centered over the southwestern U.S. continues to steer Hilda northwestward at around 7 kt. As the vortex spins down and becomes vertically shallow, Hilda is expected to turn west-northwestward and accelerate a bit as a low-level ridge builds westward across the eastern Pacific. The official NHC track forecast is largely unchanged from the previous one and lies close to the multi-model consensus. Hilda is moving over cooler waters and into a more stable environment, so continued weakening is expected over the next few days. The official NHC forecast now shows Hilda weakening to a tropical depression by Thursday morning and degenerating to a remnant low soon thereafter. The remnant low is still expected to open up into a trough this weekend well east-northeast of the Hawaiian Islands. FORECAST POSITIONS AND MAX WINDS INIT 04/0300Z 18.4N 125.5W 45 KT 50 MPH 12H 04/1200Z 19.1N 126.5W 40 KT 45 MPH 24H 05/0000Z 19.9N 128.0W 35 KT 40 MPH 36H 05/1200Z 20.7N 129.8W 30 KT 35 MPH 48H 06/0000Z 21.6N 132.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 60H 06/1200Z 22.3N 134.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 07/0000Z 22.9N 136.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 08/0000Z...DISSIPATED $$ Forecaster Reinhart/Pasch

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Tropical Storm Hilda Forecast Discussion Number 17

2021-08-03 22:39:57| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Tue Aug 03 2021 000 WTPZ43 KNHC 032039 TCDEP3 Tropical Storm Hilda Discussion Number 17 NWS National Hurricane Center Miami FL EP082021 200 PM PDT Tue Aug 03 2021 Deep convection in Hilda's central dense overcast has been weakening today, with the low-level center still on the northern side of the cloud mass. Satellite classifications have decreased since the last advisory, and a partial ASCAT pass around 1700 UTC showed maximum winds of about 45 kt. Assuming some undersampling and that the eastern radius-of-maximum winds could have been missed, the initial wind speed is set to 50 kt. A combination of shear, cool water temperatures, and a more stable environment should keep Hilda on a weakening trend throughout the forecast period. Model guidance continues to be in very good agreement, and the new NHC forecast is basically an update of the previous one. Hilda is expected to degenerate into a remnant low by Friday and dissipate as a trough this weekend well east of the Hawaiian Islands. The storm continues moving northwestward, now a little slower at about 6 kt. A mid-level ridge centered over southern California should build westward during the next few days as a mid-latitude trough along 135W moves northward out of the area. This pattern is expected to turn Hilda west-northwestward tomorrow and accelerate the cyclone in that direction as it encounters stronger low- to mid-level flow. Model guidance is a shade faster and to the left of the last cycle, and the new NHC track forecast follows that trend. FORECAST POSITIONS AND MAX WINDS INIT 03/2100Z 17.8N 125.0W 50 KT 60 MPH 12H 04/0600Z 18.5N 125.9W 45 KT 50 MPH 24H 04/1800Z 19.4N 127.2W 40 KT 45 MPH 36H 05/0600Z 20.2N 128.6W 35 KT 40 MPH 48H 05/1800Z 21.1N 130.5W 30 KT 35 MPH 60H 06/0600Z 21.9N 132.7W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 06/1800Z 22.5N 135.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 07/1800Z...DISSIPATED $$ Forecaster Blake

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Tropical Depression Ignacio Forecast Discussion Number 9

2021-08-03 22:36:49| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Tue Aug 03 2021 000 WTPZ45 KNHC 032036 TCDEP5 Tropical Depression Ignacio Discussion Number 9 NWS National Hurricane Center Miami FL EP102021 200 PM PDT Tue Aug 03 2021 Ignacio has been devoid of deep convection within 75 nmi of the center for the more than 6 hours now due to strong easterly vertical wind shear. The initial intensity has been lowered to 25 kt based on the continued degradation in the convective pattern and a 1536Z ASCAT-A scatterometer pass that revealed a patch of 27-kt surface wind vectors south of the center. The small cyclone is expected to meander over water temperatures near 26 deg C for the next 12-24 hours, while the shear is forecast to increase to near 30 kt during that time. Owing to these unfavorable environmental conditions, Ignacio is forecast to degenerate into a remnant low pressure system by late this afternoon, followed by dissipation on Wednesday. The initial motion estimate is now 090/03 kt. Ignacio is forecast to make a small clockwise loop within weak low-level steering flow until the system dissipates around 36 hours. The new NHC official track forecast is similar to the previous advisory track, and lies close to the tightly clustered simple- and corrected-consensus models. FORECAST POSITIONS AND MAX WINDS INIT 03/2100Z 20.4N 115.7W 25 KT 30 MPH 12H 04/0600Z 20.4N 115.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 04/1800Z 19.9N 114.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 05/0600Z...DISSIPATED $$ Forecaster Stewart

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