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Tropical Depression Six-E Discussion Number 3

Wiki-Hurricanes Forecast Center

200 AM PDT Thu Jun 28 2018

Six-E continues to slowly become better defined. The numerous banding features from this afternoon have congealed into one large band extending west from the center. In the absence of ASCAT and high-resolution visible imagery, the circulation itself appears to be under a developing burst of convection to the east of this band. Satellite classifications from SAB and UW-CIMSS ADT have increased to T2.0/30kt and T2.3/33kt, respectively, so the initial intensity remains a possibly conservative 30 kt. Six-E is likely to become a tropical storm later this morning.

The depression continues to move quickly west-northwest and the initial motion is set to 285/15. The forecast philosophy is largely unchanged, with a mid-level ridge to the north of the cyclone forecast to steer it on a general west-northwest course for the next 48 hours. Thereafter, a diving cut-off low from California is likely to erode the ridge and provide an outlet for Six-E to move more poleward, especially if it is a stronger entity. By day 5, however, the system is forecast to degenerate to a remnant low, allowing it to move westward within the typical low-level easterly flow.

SHIPS analysis and maps from UW-CIMSS continue to indicate moderate to strong easterly shear of 15-20 kt affecting the cyclone. This shear is forecast to slowly relax throughout the remainder of the forecast period. Despite this ever-improving upper-level forecast, sea surface temperatures are projected to decrease below 26C by 72 hours, and further fall to 23C by 96 hours. In addition, mid-level relative humidity values are forecast to fall below 60 percent after 48 hours, which may allow for intrusions of dry air into the circulation. Models across the board are less aggressive this cycle, with the GFS still making Six-E a minimal hurricane, but below the 80kt it forecast at 18z. The HWRF and SHIPS indicate a moderate tropical storm, while the FV3 and LGEM struggle to reach tropical storm strength. Thus, although the GFS has been the best performing model in the East Pacific so far this season, it appears to be the outlier and has largely been discounted. The intensity forecast remains mostly unchanged, although it is possible the current peak could be generous in light of recent data.

FORECAST POSITIONS AND MAX WINDS

INIT  28/0900Z 30 KT  35 MPH

 12H  28/1800Z 35 KT  40 MPH

 24H  29/0600Z 40 KT  45 MPH

 36H  29/1800Z 45 KT  50 MPH

 48H  30/0600Z 50 KT  60 MPH

 72H  01/0600Z 45 KT  50 MPH

 96H  02/0600Z 35 KT  40 MPH

120H  03/6000Z 25 KT  30 MPH...POST-TROP/REMNT LOW