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Tropical Storm JIMENA Forecast Discussion Number 6
2015-08-28 04:55:09| National Hurricane Center (East Pacific)
Issued at 800 PM PDT THU AUG 27 2015 000 WTPZ43 KNHC 280255 TCDEP3 TROPICAL STORM JIMENA DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132015 800 PM PDT THU AUG 27 2015 Jimena has continued to rapidly intensify. Several convective bands are tightly coiled and wrapping into the center where a small central dense overcast feature has developed during the past couple of hours. Upper-level outflow is nearly symmetrical and continues to expand. The initial intensity of 60 kt is based on a blend of consensus Dvorak satellite intensity estimates of T3.5/55 kt from TAFB and SAB, and a UW-CIMSS ADT value of T3.9/63 kt. The initial motion estimate is 270/12 kt. There is no significant change to the previous track forecast or reasoning. The NHC model guidance is tightly packed about the previous forecast track, and Jimena is expected to move westward along the southern periphery of a strong subtropical ridge for the next 36-48 hours. After that time, a turn toward the west-northwest accompanied by a decrease in forward speed is expected as a mid-latitude trough digs southward along 130-135W longitude, weakening the ridge and the steering currents. The new forecast track is essentially just an extension of the previous advisory track. Jimena has been rapidly intensifying for the past 24 hours, so the question now is how long will Jimena continue this develop trend. The surrounding atmospheric and oceanic environments are quite conducive for additional strengthening. Recent SSMI and SSMI/S microwave satellite images indicate that a nearly closed eye of 15-20 nmi diameter has formed in the low- and mid-levels, which favors continued rapid strengthening. Those same images also indicated that dry mid-level air had wrapped into the northern semicircle and had penetrated the inner-core convective region, which could hinder development. However, this hindering factor should be short lived given the very robust circulation noted in conventional satellite imagery, which should quickly mix out any dry. air intrusions. Therefore, since the vertical wind shear is forecast to remain less than 10 kt, rapid intensification is forecast to continue for another 36 hours or so. After that time, the expected intense circulation of Jimena should begin to create cold upwelling since the cyclone will be moving over significantly lower upper ocean heat content values, which should cap the intensification process and induce slow weakening by days 4 and 5. The official intensity forecast is similar to the previous advisory, and lies between the forecasts of the SHIPS and LGEM models, which have performed quite well thus far with Jimena. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 12.3N 119.9W 60 KT 70 MPH 12H 28/1200Z 12.3N 121.7W 75 KT 85 MPH 24H 29/0000Z 12.4N 123.7W 90 KT 105 MPH 36H 29/1200Z 12.6N 125.6W 105 KT 120 MPH 48H 30/0000Z 13.2N 127.3W 110 KT 125 MPH 72H 31/0000Z 14.8N 131.7W 125 KT 145 MPH 96H 01/0000Z 16.5N 136.0W 120 KT 140 MPH 120H 02/0000Z 17.5N 139.0W 110 KT 125 MPH $$ Forecaster Stewart
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