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Post-Tropical Cyclone Polo Forecast Discussion Number 9

2020-11-19 21:32:50| National Hurricane Center (East Pacific)

Issued at 100 PM PST Thu Nov 19 2020 000 WTPZ41 KNHC 192032 TCDEP1 Post-Tropical Cyclone Polo Discussion Number 9 NWS National Hurricane Center Miami FL EP212020 100 PM PST Thu Nov 19 2020 A few convective cells continue to pulse over 100 n mi northeast of Polo's center, but overall the cyclone has not produced persistent, organized deep convection since yesterday evening. Therefore, Polo is being designated as a remnant low. A recent ASCAT pass sampled the eastern part of Polo's circulation and showed winds around 25 kt, so it is assumed that 30-kt winds are still occurring closer to the center. Moderate westerly shear, marginally warm waters, and a dry environment should cause Polo's winds to gradually decrease, and the circulation is expected to open up into a trough by 36 hours, per the latest global model guidance. Polo is moving just south of due west (265/10 kt), steered by a low- to mid-level ridge to its north. This general motion is expected to continue until the low dissipates, and the NHC track forecast is down the middle of the tightly packed guidance envelope. 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 19/2100Z 16.9N 121.3W 30 KT 35 MPH...POST-TROP/REMNT LOW 12H 20/0600Z 16.9N 122.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 20/1800Z 16.8N 125.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 21/0600Z...DISSIPATED $$ Forecaster Berg

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Tropical Depression Polo Forecast Discussion Number 8

2020-11-19 15:33:43| National Hurricane Center (East Pacific)

Issued at 700 AM PST Thu Nov 19 2020 000 WTPZ41 KNHC 191433 TCDEP1 Tropical Depression Polo Discussion Number 8 NWS National Hurricane Center Miami FL EP212020 700 AM PST Thu Nov 19 2020 Occasional bursts of deep convection have been developing to the east and northeast of Polo's center since yesterday evening, but none have lasted for more than about an hour or two. ASCAT-C data received after the scatterometer pass noted in the previous advisory did not explicitly show tropical-storm-force winds, suggesting that Polo continues to weaken, and the most recent Dvorak CI numbers from TAFB and SAB are 2.0. For these reasons, Polo is now assumed to be a 30-kt tropical depression. Polo has not maintained enough organized convection to be considered a tropical cyclone for the last 12 to 15 hours, and if sustained convection does not redevelop soon, the system will likely be declared a remnant low later this afternoon. The remnant low is expected to continue weakening due to westerly shear, only marginally warm waters, and dry air, and it is expected to dissipate by 48 hours, if not sooner. Polo is being steered westward (275/10 kt) to the south of a low- to mid-level ridge. Once Polo becomes a remnant low, the shallow circulation should take on a south-of-due-west motion in about 24 hours, continuing that trajectory until it dissipates. This pattern is shown by nearly all the reliable track models, and the NHC forecast lies down the middle of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 19/1500Z 17.1N 120.3W 30 KT 35 MPH 12H 20/0000Z 17.1N 121.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 20/1200Z 17.0N 123.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 21/0000Z 16.7N 126.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 21/1200Z...DISSIPATED $$ Forecaster Berg

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Tropical Storm Polo Forecast Discussion Number 7

2020-11-19 09:48:07| National Hurricane Center (East Pacific)

Issued at 100 AM PST Thu Nov 19 2020 000 WTPZ41 KNHC 190848 TCDEP1 Tropical Storm Polo Discussion Number 7 NWS National Hurricane Center Miami FL EP212020 100 AM PST Thu Nov 19 2020 Polo has been devoid of deep convection near the center for more than 6 hours. However, a narrow band of convection with cloud tops to -60 to -70 deg C has recently developed in the northeastern quadrant 30-40 nmi from the center, in the same location where a 0439Z partial ASCAT-B scatterometer pass indicated a few surface wind vectors of 34-35 kt. Therefore, Polo is being maintained as a tropical storm with an intensity of 35 kt for this advisory. The initial motion estimate is now 280/10 kt. A low-/mid-level ridge situated to the north of Polo should steer the small cyclone generally westward until it dissipates in a day or two. The new NHC track forecast is similar to but a tad south of the previous advisory track, and lies close to the tightly packed consensus models TVCE, GFEX, and NOAA-HCCA. Over the next two days, Polo is forecast to move into a less favorable environment consisting of moderate-to-strong westerly shear, a drier and more stable air mass, and sea-surface temperatures less than 26 deg C. As a result, convection should steadily weaken, causing Polo to gradually spin down and become a remnant low by this afternoon or tonight, and dissipate by 60 hours, if not sooner. The official intensity forecast is similar to the previous advisory, and closely follows the intensity consensus models IVCN and HCCA. FORECAST POSITIONS AND MAX WINDS INIT 19/0900Z 17.1N 119.3W 35 KT 40 MPH 12H 19/1800Z 17.1N 120.9W 30 KT 35 MPH 24H 20/0600Z 17.1N 123.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 20/1800Z 17.0N 125.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 21/0600Z 16.6N 128.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 21/1800Z...DISSIPATED $$ Forecaster Stewart

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Tropical Storm Polo Forecast Discussion Number 6

2020-11-19 03:34:31| National Hurricane Center (East Pacific)

Issued at 700 PM PST Wed Nov 18 2020 000 WTPZ41 KNHC 190234 TCDEP1 Tropical Storm Polo Discussion Number 6 NWS National Hurricane Center Miami FL EP212020 700 PM PST Wed Nov 18 2020 Satellite imagery shows that the convection associated with Polo has diminished this evening, with the remaining convection now to the east of the exposed low-level center. The initial intensity is held at a possibly generous 35 kt as a blend of subjective and objective satellite intensity estimates. Polo is moving into an environment of moderate westerly shear, a dryer air mass, and decreasing sea surface temperatures, and the system should gradually weaken during the next 48 h. The new intensity forecast has minor adjustments from the previous forecast, and it calls for Polo to degenerate to a remnant low by 36 h and dissipate by 60 h. The initial motion is 285/11. A low-level ridge to the north of the cyclone should steer the system generally westward until it dissipates. and the new track forecast is an update of the previous forecast. FORECAST POSITIONS AND MAX WINDS INIT 19/0300Z 16.9N 118.3W 40 KT 45 MPH 12H 19/1200Z 17.2N 119.9W 35 KT 40 MPH 24H 20/0000Z 17.3N 122.0W 30 KT 35 MPH 36H 20/1200Z 17.3N 124.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 21/0000Z 17.3N 126.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 21/1200Z...DISSIPATED $$ Forecaster Beven

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Tropical Storm Polo Forecast Discussion Number 5

2020-11-18 21:33:27| National Hurricane Center (East Pacific)

Issued at 100 PM PST Wed Nov 18 2020 000 WTPZ41 KNHC 182033 TCDEP1 Tropical Storm Polo Discussion Number 5 NWS National Hurricane Center Miami FL EP212020 100 PM PST Wed Nov 18 2020 While the cloud pattern was fairly well organized this morning, Polo provided a little surprise when the center popped out of the central dense overcast. The system has since developed deep convection near the center, so perhaps this was a temporary fluctuation but reflects marginal environmental conditions. The initial wind speed is kept at 40 kt as a blend of the satellite data, and unfortunately scatterometer data missed again for a more certain estimate. Polo probably will peak in intensity during the next 12 hours or so before a combination of higher shear and dry/stable air causes the storm to weaken and eventually become a remnant low on Friday. No significant changes were made to the intensity forecast, and there were no meaningful model outliers from the NHC prediction. At least the exposed center allowed for a more precise initial motion estimate, though it ended up about the same as before 285/10. Model guidance is tightly clustered on the storm turning westward tomorrow while it remains to the south of a low- to mid-level ridge. The small cyclone will likely decay into a trough of low pressure by the weekend. Only cosmetic changes were made to the last forecast, which continues to lie near or just south of the model consensus. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 16.5N 117.2W 40 KT 45 MPH 12H 19/0600Z 16.8N 118.9W 40 KT 45 MPH 24H 19/1800Z 17.0N 120.9W 35 KT 40 MPH 36H 20/0600Z 17.1N 123.0W 30 KT 35 MPH 48H 20/1800Z 17.1N 125.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 21/0600Z...DISSIPATED $$ Forecaster Blake

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