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Tropical Storm Carlos Forecast Discussion Number 3
2021-06-13 10:36:43| National Hurricane Center (East Pacific)
Issued at 200 AM PDT Sun Jun 13 2021 000 WTPZ43 KNHC 130836 TCDEP3 Tropical Storm Carlos Discussion Number 3 NWS National Hurricane Center Miami FL EP032021 200 AM PDT Sun Jun 13 2021 Infrared and scatterometer satellite data indicate that Carlos remains a compact tropical cyclone. Two ASCAT passes between 0400-0500 UTC revealed a radius of maximum wind of 10-12 nmi and tropical-storm-force winds that only extended outward about 20 nmi. Cloud tops colder than -50C only extend outward about 60 nmi from the center. The earlier ASCAT-A/-B passes contained peak surface wind vectors of 37 kt/40 kt, respectively, so the estimated intensity has been increased to 40 kt for this advisory, which could be a little conservative owing to the small size of the cyclone and possible undersampling of the scatterometer instrument. The initial motion estimate is due west or 270/07 kt. There is little change to the previous NHC track forecast or reasoning. The latest model runs are in good agreement on Carlos turning toward the west-southwest later today, followed by a southwestward motion on Monday and Tuesday as a low- to mid-level ridge to the north of the cyclone builds southward. By day 3, the models diverge significantly when the deep-layer steering currents collapse, followed by possible rapid weakening. The ECMWF weakens Carlos into a shallow remnant low by 72 h, with the shallow vortex then being driven southwestward by a strong low-level ridge to the north and northeast. In contrast, the GFS and some of the other global and regional models keep Carlos stronger and vertically deeper, which results in a ridge to the east lifting the cyclone out toward the north. Given the large spread in the track guidance on days 4 and 5, the new NHC track forecast is similar to but slightly slower than the previous advisory track, and close to a blend of the TVCE and GFEX simple consensus track models. Carlos' small size in combination with the relatively low deep-layer vertical shear of 5-10 kt for the next 36 h or so would normally argue for significant strengthening. However, the cyclone's proximity to very dry mid-level and cooler sea-surface just to its north and northwest is expected to result in the periodic entrainment of stable air for the 72 h or so, resulting in intermittent disruptions of the central deep convection. Thus, little change in strength is forecast during that time. Thereafter, the combination of increasing southwesterly wind shear and sub-27C sea-surface temperatures along the track is expected to induce gradual weakening. The official intensity forecast is similar to the previous advisory, and closely follows the IVCN and HCCA intensity consensus models. FORECAST POSITIONS AND MAX WINDS INIT 13/0900Z 11.9N 125.3W 40 KT 45 MPH 12H 13/1800Z 11.6N 126.1W 45 KT 50 MPH 24H 14/0600Z 11.2N 126.9W 45 KT 50 MPH 36H 14/1800Z 10.7N 127.4W 45 KT 50 MPH 48H 15/0600Z 10.3N 127.7W 45 KT 50 MPH 60H 15/1800Z 10.2N 128.0W 40 KT 45 MPH 72H 16/0600Z 10.6N 128.1W 40 KT 45 MPH 96H 17/0600Z 12.0N 128.2W 35 KT 40 MPH 120H 18/0600Z 14.0N 127.9W 30 KT 35 MPH $$ Forecaster Stewart
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