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Tropical Depression Eight-E Forecast Discussion Number 5
2017-07-19 16:41:49| National Hurricane Center (East Pacific)
Issued at 800 AM PDT Wed Jul 19 2017 000 WTPZ43 KNHC 191441 TCDEP3 Tropical Depression Eight-E Discussion Number 5 NWS National Hurricane Center Miami FL EP082017 800 AM PDT Wed Jul 19 2017 The center of the depression is challenging to locate this morning with lots of disorganized convection in the vicinity of the apparent center. Microwave data suggest it is on the northeast side of the convective mass, although it doesn't agree that well with the overnight ASCAT data. The initial position tries to keep continuity from the overnight advisory, since there was a direct ASCAT hit at 0600Z, but it may have to be revised when visible imagery is available. The initial wind speed is kept at 30 kt, based on a blend of the TAFB/SAB fixes. Unfortunately the forecast of the depression isn't any easier than locating it. Some binary interaction with the circulation of Tropical Storm Greg is likely over the next few days since the cyclones should be moving fairly close to one another. This pattern would probably steer the depression southwestward, then northwestward by day 3 as Greg passes to the north and begins to draw the depression closer to it. The specifics of this interaction, however, are impossible to determine at this range because it also depends on how strong and exactly where the two systems are. It is becoming increasingly likely that Greg will be the more dominant and stronger system, causing the depression to take a more southward track, and would potentially absorb the depression in 4-5 days. The official forecast is shifted southward in the short-term to account for the latest model guidance, but is fairly close to the previous forecast at the end of the period. The intensity forecast is also tricky because many of the global models suggest that there is a window of lower shear between when the northwesterly outflow-related shear from Fernanda weakens and shifts to easterly shear related to the circulation and outflow from Greg. Most of the guidance, however, does not respond much to the lower shear, suggesting little change in intensity during the next couple of days. The new intensity forecast remains close to the model consensus and the previous NHC prediction, though the cyclone does have a small chance to become a tropical storm. The majority of the global models are showing the depression degenerating into a trough by day 4 due to increasing shear and interaction with the circulation of Greg, so the NHC forecast follows suit. It should be noted that this is a very uncertain forecast due to the unusually high number of difficult-to-predict variables. FORECAST POSITIONS AND MAX WINDS INIT 19/1500Z 14.5N 121.1W 30 KT 35 MPH 12H 20/0000Z 14.0N 121.8W 30 KT 35 MPH 24H 20/1200Z 13.3N 122.6W 30 KT 35 MPH 36H 21/0000Z 12.6N 123.3W 30 KT 35 MPH 48H 21/1200Z 12.3N 123.6W 30 KT 35 MPH 72H 22/1200Z 13.0N 124.5W 25 KT 30 MPH 96H 23/1200Z...DISSIPATED $$ Forecaster Blake
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