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Tropical Storm Polo Forecast Discussion Number 4
2020-11-18 15:40:59| National Hurricane Center (East Pacific)
Issued at 700 AM PST Wed Nov 18 2020 000 WTPZ41 KNHC 181440 TCDEP1 Tropical Storm Polo Discussion Number 4 NWS National Hurricane Center Miami FL EP212020 700 AM PST Wed Nov 18 2020 Satellite images indicate that the depression has strengthened into a tropical storm. The small central dense overcast has grown during the past several hours and a few banding features have formed. Dvorak estimates range from 30 to 45 kt, and the initial wind speed is set to 40 kt, which matches the latest CIMSS satellite consensus estimate. Polo could strengthen a little more today, but an increase in shear and dry-air entrainment should start the weakening process on Thursday, with the system expected to become a non-convective remnant low on Friday. The new NHC forecast is a little below the model consensus, close to the previous NHC forecast, leaning toward the idea that the small tropical cyclone will probably weaken faster than the bulk of the guidance anticipates. The initial motion continues to be west-northwestward at 10 kt. There has been no change to the forecast philosophy, with Polo forecast to remain on the southern side of a mid-level ridge throughout the period. The storm should turn more westward on Thursday as the system weakens and becomes more shallow. The new forecast is south of the latest model consensus, nudged slightly north of the previous NHC forecast. FORECAST POSITIONS AND MAX WINDS INIT 18/1500Z 16.3N 116.0W 40 KT 45 MPH 12H 19/0000Z 16.5N 117.6W 40 KT 45 MPH 24H 19/1200Z 16.7N 119.6W 35 KT 40 MPH 36H 20/0000Z 16.9N 121.5W 30 KT 35 MPH 48H 20/1200Z 17.0N 123.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 21/0000Z 17.0N 126.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 21/1200Z...DISSIPATED $$ Forecaster Blake
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Tropical Depression Iota Forecast Discussion Number 20
2020-11-18 09:38:39| National Hurricane Center (Atlantic)
Issued at 300 AM CST Wed Nov 18 2020 309 WTNT41 KNHC 180838 TCDAT1 Tropical Depression Iota Discussion Number 20 NWS National Hurricane Center Miami FL AL312020 300 AM CST Wed Nov 18 2020 Deep convection is no longer occurring near Iota's center, but curved broken bands of convection still exist within 100 n mi in the northern semicircle. For that reason, Iota is being maintained as a tropical cyclone. Earlier ASCAT and ScatSat scatterometer data between 0200-0300 UTC indicated surface winds of 30-32 kt offshore the north-central coast of Honduras, while tropical-storm-force wind gusts were noted in surface observations along the north coast of Honduras. As a result, the intensity was maintained at 35 kt at the 0600 UTC synoptic time. Since then, however, winds have decreased along the coast and offshore, which justify making Iota a 30-kt tropical depression at the 0900 UTC advisory time. Therefore, the Tropical Storm Warning for the northern coast of Honduras has been discontinued. The initial motion estimate is now 255/11 kt. Iota or its remnants should continue moving west-southwestward across El Salvador, possibly emerging over the eastern North Pacific Ocean as a post-tropical cyclone before dissipation occurs by late today. At this time, most of the available NHC model guidance does not show regeneration over the eastern Pacific, with only the HWRF and HMON regional models showing brief redevelopment to tropical depression status on Thursday after Iota degenerates to a remnant low later today. However, this is considered a low probability alternate scenario due to unfavorable upper-level winds expected across the eastern North Pacific. Iota is still expected to produce very serious flash flooding and mud slides. These hazards could result in potentially catastrophic effects, especially when compounded upon Hurricane Eta's destruction from a couple of weeks ago. Key Messages: 1. Life-threatening flash flooding and river flooding is expected through Thursday across portions of Central America due to heavy rainfall from Iota. Flooding and mudslides across portions of Honduras, Nicaragua and Guatemala could be exacerbated by saturated soils in place, resulting in significant to potentially catastrophic impacts. FORECAST POSITIONS AND MAX WINDS INIT 18/0900Z 13.7N 88.3W 30 KT 35 MPH...INLAND EL SALVADOR 12H 18/1800Z 13.0N 89.9W 20 KT 25 MPH...POST-TROP/REMNT LOW 24H 19/0600Z...DISSIPATED $$ Forecaster Stewart
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Tropical Depression Twenty-one-E Forecast Discussion Number 3
2020-11-18 09:36:41| National Hurricane Center (East Pacific)
Issued at 100 AM PST Wed Nov 18 2020 000 WTPZ41 KNHC 180836 TCDEP1 Tropical Depression Twenty-One-E Discussion Number 3 NWS National Hurricane Center Miami FL EP212020 100 AM PST Wed Nov 18 2020 The curved band feature that was prominent in earlier satellite images has dissipated, likely due to very dry air surrounding the cyclone. The depression now consists of a small central dense overcast (CDO) that has just recently become established in the past few hours. Earlier ASCAT data indicated that the strongest winds were occurring to the west of the center of the depression, near the curved band that existed at that time, while winds of 20-25 kt were occurring around the center. The nearest sampling by a scatterometer tonight was by the ASCAT-A, which did pass over some of the same area that had the strongest winds earlier, with peak winds now only 20 kt. Assuming the reorganizing of the convection near the center has helped to increased the winds somewhat there, the initial intensity is being held at 30 kt. If the current CDO feature persists this morning, then the depression will likely strengthen to a tropical storm later today. By early Thursday, moderate west-southwesterly shear, cooler oceanic temperatures, and the presence of a very dry and stable air mass should cause the cyclone to begin weakening, and by Thursday night the system is expected to degenerate to a remnant low. The latest NHC intensity forecast is unchanged from the previous one and is in agreement with the various multimodel consensus aids. The initial motion continues to be west-northwestward at 10 kt. The depression is moving to the south of a mid-level ridge, and the cyclone is expected to continue in this general motion through tonight. A turn to the west within the low-level easterly trade wind flow is expected on Thursday as the system loses its deep convection and becomes shallow. The track forecast was nudged a little to the left of the previous advisory track due to a shift in the model guidance in that direction. FORECAST POSITIONS AND MAX WINDS INIT 18/0900Z 15.7N 115.2W 30 KT 35 MPH 12H 18/1800Z 16.1N 116.8W 35 KT 40 MPH 24H 19/0600Z 16.5N 118.9W 35 KT 40 MPH 36H 19/1800Z 16.7N 120.9W 30 KT 35 MPH 48H 20/0600Z 16.8N 123.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 20/1800Z 16.8N 125.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 21/0600Z...DISSIPATED $$ Forecaster Latto
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Tropical Depression Twenty-One-E Forecast Discussion Number 2
2020-11-18 03:37:07| National Hurricane Center (East Pacific)
Issued at 800 PM MST Tue Nov 17 2020 000 WTPZ41 KNHC 180236 TCDEP1 Tropical Depression Twenty-One-E Discussion Number 2 NWS National Hurricane Center Miami FL EP212020 800 PM MST Tue Nov 17 2020 Conventional satellite imagery and an earlier AMSR2 microwave pass showed curved bands developing over the western portion of the cyclone, although deep convection remains rather limited near the depression's surface center. Subjective satellite intensity estimate T-numbers haven't changed during the past 6 hours and the initial intensity is held at 30 kt for this advisory. The HCCA and IVCN multi-model intensity aids along with the LGEM model indicate that the depression will strengthen to a low-end tropical storm during the next 12-24 hrs and the NHC forecast continues to show this trend. Afterward, modest west-southwesterly shear, cooler oceanic temperatures, and the presence of a very dry and stable air mass should cause the cyclone to weaken and degenerate to a remnant low in 2 days. The deterministic guidance agrees that the depression will open up into a trough of low pressure in 4 days, or less. This is also reflected in the official intensity forecast. The initial motion is estimated to be west-northwestward, or 285/10 kt in the mid-tropospheric steering current provided by high pressure anchored to the north of the cyclone. The depression is expected to continue in this general motion through Thursday. Through the remaining forecast period, the depression is forecast to turn westward in the low-level easterly flow as a shallow, or vertically limited cyclone. The track forecast is basically an update of the previous one and is close to the HCCA and TVCE consensus models. FORECAST POSITIONS AND MAX WINDS INIT 18/0300Z 15.5N 114.3W 30 KT 35 MPH 12H 18/1200Z 15.9N 115.9W 35 KT 40 MPH 24H 19/0000Z 16.5N 118.0W 35 KT 40 MPH 36H 19/1200Z 16.9N 120.0W 30 KT 35 MPH 48H 20/0000Z 17.3N 122.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 20/1200Z 17.3N 124.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 21/0000Z...DISSIPATED $$ Forecaster Roberts
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Tropical Storm Iota Forecast Discussion Number 19
2020-11-18 03:35:37| National Hurricane Center (Atlantic)
Issued at 900 PM CST Tue Nov 17 2020 000 WTNT41 KNHC 180235 TCDAT1 Tropical Storm Iota Discussion Number 19 NWS National Hurricane Center Miami FL AL312020 900 PM CST Tue Nov 17 2020 Most of the deep convection associated with Iota has weakened during the past several hours, with the primary remaining convection now in a band well removed from the center in the northwestern semicircle. The initial intensity is reduced to 35 kt, and these winds are possibly occuring in two areas - a small area near what is left of the inner core and along the coast of Honduras in the Tropical Storm warning area. Iota should continue to quickly weaken, with the system expected to drop below tropical-storm strength during the next few hours and to dissipate completely between 12-24 h. At this time, the available guidance is not bullish on any regeneration of the system over the Pacific. The initial motion is 270/10. The cyclone or its remnants should move westward to west-southwestward before dissipation occurs. Iota is still expected to produce very serious hazards while it is over central America, including flash flooding and mud slides, These hazards could result in potentially catastrophic effects, especially when compounded upon Hurricane Eta's destruction from a couple of weeks ago. Key Messages: 1. Life-threatening flash flooding and river flooding is expected through Thursday across portions of Central America due to heavy rainfall from Iota. Flooding and mudslides across portions of Honduras, Nicaragua and Guatemala could be exacerbated by saturated soils in place, resulting in significant to potentially catastrophic impacts. 2. Tropical-storm conditions, primarily close to the center of Iota and along the coast of Honduras, are still expected for the next few hours. FORECAST POSITIONS AND MAX WINDS INIT 18/0300Z 13.7N 87.3W 35 KT 40 MPH...INLAND 12H 18/1200Z 13.4N 88.7W 25 KT 30 MPH...POST-TROP/INLAND 24H 19/0000Z...DISSIPATED $$ Forecaster Beven
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