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Tropical Depression Twelve-E Discussion Number 1

Wiki-Hurricanes Forecast Center

2:00 PM PDT Sun Aug 5 2018

The sprawling disturbance located about 400 miles southwest of Acapulco, Mexico, has acquired enough organization to be declared a tropical depression. It isn't particularly defined at the current time, with numerous spiral bands wrapping into a generally rain-free center of circulation. Nonetheless, SAB analysis yielded T2.0/30kt at 18z, and the initial intensity is set at that value.

The newly-formed system is moving steadily northwest today toward a weakness in the mid-level ridge that stretches from offshore California into the US Central Plains. This motion should continue for the next 72 hours before the system reaches the western periphery of the high pressure thereafter, causing a turn toward the west-northwest. Models are in excellent agreement with the track of Twelve-E, yielding a high confidence forecast in this regard.

As mentioned earlier, Twelve-E is a broad and disorganized system at initialization, although there are signs of convection beginning to develop near the center in the most recent satellite frames. The environment favors significant strengthening, with wind shear generally near or under 5kt for the next 5 days. Mid-level relative humidity values start off around 75 percent and only decrease to near 65 percent by day 5. Ocean temperatures currently reside near 30C and will remain fairly constant until Twelve-E approaches the sharp SST gradient about 72 hours from now. So that said, the only limiting factors for our cyclone are its broad size and time. Model guidance is generally aggressive, with the SHIPS and LGEM indicating peaks of 108kt and 94kt, respectively. The 12z GFS bottoms out at 938mb while both the UKMET and ECMWF reach 957mb. For now, the updated forecast shows steady intensification to a peak of 100kt in 72 hours, followed by quick weakening thereafter over colder waters. This could be a little conservative.

FORECAST POSITIONS AND MAX WINDS

INIT 05/2100Z 30 KT 35 MPH

12H 06/0600Z 40 KT 45 MPH

24H 06/1800Z 55 KT 65 MPH

36H 07/0600Z 70 KT 80 MPH

48H 07/1800Z 85 KT 100 MPH

72H 08/1800Z 100 KT 115 MPH

96H 09/1800Z 70 KT 80 MPH

120H 10/1800Z 40 KT 45 MPH

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