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Tropical Storm Erick Forecast Discussion Number 5
2019-07-28 16:39:44| National Hurricane Center (East Pacific)
Issued at 500 AM HST Sun Jul 28 2019 000 WTPZ41 KNHC 281439 TCDEP1 Tropical Storm Erick Discussion Number 5 NWS National Hurricane Center Miami FL EP062019 500 AM HST Sun Jul 28 2019 The convective cloud pattern has changed little overall since the previous advisory, with the main cloud mass displaced into the southern semicircle due to some northerly mid-level shear. A late-arriving 0615Z ASCAT-C scatterometer pass along with passive microwave imagery indicate that the low-level center is positioned near the northern edge of the central convective cloud mass. However, the upper-level outflow has continued to improve and expand in all quadrants. The scatterometer pass showed only a few 33-kt surface wind vectors in the northeastern quadrant, so the advisory intensity remains at 35 kt, which is in agreement with 35-kt Dvorak satellite estimates from both TAFB and SAB. The initial motion is 275/15 kt. A slight westward jog has occurred during the past 6 hours, likely due to the southward shift in the convective cloud mass. However, resumption of the earlier base motion of 280 degrees is expected later today when the shear decreases and the convective cloud pattern becomes more symmetrical. Overall, there is no significant change to the previous forecast track rationale. A narrow but well-defined low to mid-level ridge is forecast by the global models to build westward across the Hawaiian Islands through the entire forecast period, which is expected to keep Erick moving generally westward to slightly west-northwestward. On the forecast track, Erick is expected to cross into the Central Pacific basin on Tuesday, and the new NHC model guidance remains in good agreement on this track scenario. The new official forecast track is a little south of the previous advisory track, mainly due to the more southerly initial position, and lies close to a blend of the consensus track models HCCA and TVCE. Convective banding has started to increase during the past few hours, along with the development of a small CDO feature. The aforementioned ASCAT-C pass revealed that Erick has a small radius of maximum winds (RMW) of about 20 nmi. The small RMW, low vertical wind shear of about 5 kt, and SSTs near 28C support at least steady strengthening at a typical climatological rate of 20 kt per 24 hours for the next 2-3 days. As a result, Erick is forecast to become a hurricane in 36 hours. Although rapid intensification (RI) is a possibility due to the small RMW and low shear, a dry mid-level environment is expected to hinder RI through 72 hours when stronger vertical wind shear is forecast to affect the cyclone and disrupt the intensification process. Thereafter, steady weakening due to westerly wind shear increasing to more than 20 kt is expected, resulting in Erick becoming a tropical storm by 120 hours. It is worth mentioning that although the Navy COAMPS model is forecasting Erick to become a category-4 hurricane by 72 hours, this scenario has been disregarded at this time due to the abundance of dry mid-level surrounding cyclone. The official intensity forecast is similar to the previous NHC advisory, and closely follows the HCCA corrected consensus model. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 12.3N 129.8W 35 KT 40 MPH 12H 29/0000Z 12.6N 132.0W 45 KT 50 MPH 24H 29/1200Z 13.1N 134.9W 55 KT 65 MPH 36H 30/0000Z 13.6N 137.6W 65 KT 75 MPH 48H 30/1200Z 14.3N 140.3W 75 KT 85 MPH 72H 31/1200Z 15.6N 145.0W 85 KT 100 MPH 96H 01/1200Z 16.6N 149.6W 65 KT 75 MPH 120H 02/1200Z 17.1N 154.8W 45 KT 50 MPH $$ Forecaster Stewart
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