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Tropical Storm Carlos Forecast Discussion Number 2
2021-06-13 04:56:06| National Hurricane Center (East Pacific)
Issued at 800 PM PDT Sat Jun 12 2021 000 WTPZ43 KNHC 130256 TCDEP3 Tropical Storm Carlos Discussion Number 2 NWS National Hurricane Center Miami FL EP032021 800 PM PDT Sat Jun 12 2021 Satellite imagery indicates improved organization this evening as a cold convective burst has expanded over the estimated low-level circulation center. A 2032 UTC AMSR2 microwave pass indicated that underneath this convective burst was also improved convective banding, especially over the southern semicircle. The latest round of Dvorak satellite estimates were T2.0/30 kt from TAFB and T2.5/35 kt from SAB. The most recent UW-CIMSS Advanced Dvorak Technique value was also T2.5/35 kt. Favoring the higher intensity estimates, and assuming some intensification has occurred from the earlier scatterometer passes, Tropical Depression Three-E has been upgraded to Tropical Storm Carlos with an advisory intensity of 35 kt. Carlos appears to be gradually turning leftward and slowing down this evening, with the most recent estimated motion at 270/06 kt. The mid-level ridge north of Carlos is forecast to gradually weaken, shift northward, and then be replaced by a deep-layer trough that will essentially shut down the steering currents near the cyclone after 24 h. Between 36 to 48 h the motion of Carlos is likely to slow to a crawl, generally to the west-southwest. By 72 h, another mid-to-upper level trough digging in from the northwest will finally induce some northerly steering, helping Carlos to gradually accelerate to the north. The latest track forecast is a bit west of the previous NHC forecast owing to the current motion, but remains very close to the HFIP corrected consensus and TCVE track consensus. It should be noted that there remains large spread in the guidance on how quickly Carlos slows down, with the latest GFS forecast slowing down the cyclone almost immediately, while the CMC and ECMWF runs show a much faster track to the west-southwest. The intensity forecast is tricky due to both the small size of the tropical cyclone and also the less than optimal environment surrounding the system. While deep-layer vertical wind shear is only expected to be low to moderate over the next 72 h, mid-level shear out of the north to northwest is a bit higher (15-25 kt) and could occasionally import very dry mid-level air from that direction. In fact, ECMWF-SHIPS mid-level humidity values gradually decrease to under 500ver the next 36 h. In addition, the very slow motion of Carlos expected between 24-72 h could potentially upwell cooler sea-surface temperatures than the current 27-28 C values along the forecast track. For this reason, the latest NHC intensity forecast is fairly conservative, forecasting a peak intensity of 45 kt between 24-60 h, which is close to the HFIP corrected consensus and peak intensity of the most recent HWRF run. Thereafter, as the storm begins to gain latitude, increasingly dry, stable air in addition to decreasing sea surface temperatures should lead to gradual weakening beyond 60 h. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 11.9N 124.5W 35 KT 40 MPH 12H 13/1200Z 11.8N 125.5W 40 KT 45 MPH 24H 14/0000Z 11.4N 126.5W 45 KT 50 MPH 36H 14/1200Z 10.8N 127.2W 45 KT 50 MPH 48H 15/0000Z 10.6N 127.4W 45 KT 50 MPH 60H 15/1200Z 10.3N 127.7W 45 KT 50 MPH 72H 16/0000Z 10.3N 128.0W 40 KT 45 MPH 96H 17/0000Z 11.5N 128.1W 35 KT 40 MPH 120H 18/0000Z 13.5N 127.9W 30 KT 35 MPH $$ Forecaster Papin/Pasch
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