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Tropical Storm Eleven-E Discussion Number 4

Wiki-Hurricanes Forecast Center

8:00 AM PDT Sun Aug 5 2018

Despite only having existed for about a day, Eleven-E has been a particularly peculiar tropical cyclone. Frequent fluctuations in appearance have kept us on our toes, and this morning appears to feature a new round of rather quick development. Although northerly wind shear is evident on satellite imagery, convective activity has made a surge northward and a fair number of banding features are beginning to take shape south of the center of circulation. Microwave data confirms what can be observed on infrared imagery and shows more refinement to the storm's core structure. Cloud tops are certainly quite cold, with a fair expanse of -80°C and colder cloud tops near the center. Unfortunately, there have not been any recent scatterometer passes to investigate the enigmatic system, and microwave data can only loosely pick up on 30 kt winds in select locations. SAB estimates T2.0/30kt, though automated estimates are much higher with UW-CIMSS ADT giving T2.8/41kt and NHC ADT showing T2.9/43kt. Based on the improved satellite appearance and an improving core, Eleven-E has been upgraded to a 35 kt tropical storm.

Eleven-E is steadily making its way to the northwest or west-northwest thanks to a 594 dm mid-level ridge centered over southern Georgia, with the northerly component being provided by a mid-level inverted trough currently over Mexico. With both features extending or tracking west in concert with Eleven-E, this motion is expected initially today and possibly fo rthe early part of tomorrow. Some chaotic motion influenced by Fujiwhara interaction could take place as Eleven-E intertwines with a new system expected to become a tropical cyclone to the system's west, and absorption by this tropical cyclone seems likely. Eleven-E probably has about two to three days as an independent tropical cyclone before it is absobred by the nearby tropical cyclone. Absorption is more likely to occur sooner rather than later as models seem to hold on to an independent pressure field for too long, but much of Eleven-E's future is dependent on how the disturbance to its west, designated as Invest 95E, develops.

Eleven-E's intensity forecast is somewhat complex given the rather frenzied envrionment which the tropical storm finds itself in. Wind shear is expected to remain generally high as the system west of Eleven-E develops into a tropical cyclone, keeping a northerly flow over the tropical storm. A cold tropopause, very warm waters, and plentifully moist air could contribute to very deep and explosive convection, but the persistent wind shear should prevent Eleven-E from making too much progress with its organization. Most statistical guidance appears to be entranced by the warm waters and ramp Eleven-E up to a hurricane, seemingly ignoring the presence of a likely nearby tropical cyclone which the same guidance shows as being equally strong and tracking very much in the same direction, so these can be for the most part ignored. Dynamical and synoptic guidance are probably more useful in this situation. Global guidance generally keeps Eleven-E fairly weak, while HMON and HWRF both shape Eleven-E into a microscale hurricane with gale-force winds at times extending less than 40 nmi from the center. I am betting that the dynamical hurricane guidance is way too aggressive and tries to do too much in making the pressure field too small and placing it in the circulation of a larger tropical cyclone, creating a scenario where the model observes fantastical amounts of lower convergence which it reads as intensification. Out of the model suite, the ECMWF IFS looks to be the most levelheaded, and shows a moderate tropical storm. For now, a fairly basic increase and decrease in strength is depicted in the forecast, showing some strengthening today as Eleven-E remains an independent tropical cyclone. Tomorrow, Eleven-E is expected to begin wrapping into a new tropical cyclone to the west, which should stretch the circulation and eventually splice it apart in a projected 72 hours.

FORECAST POSITIONS AND MAX WINDS

INIT 05/1500Z 35 KT 40 MPH

12H 06/0000Z 40 KT 45 MPH

24H 06/1200Z 45 KT 50 MPH

36H 07/0000Z 45 KT 50 MPH

48H 07/1200Z 35 KT 40 MPH

72H 08/1200Z...DISSIPATED

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