Tropical Weather Discussion

by Gary Gray




...Epsilon Beginning Clockwise Loop [12/6 10PM EST]...



Hurricane Epsilon continues to be intriguing for its uniqueness, but otherwise a dull footnote. It is unique in that it is a rare December hurricane (there have been several December tropical storms, but only a handful of hurricanes). It is also unique in that it has held it's own, and even strengthened at times, over 68-72F waters, and few forecasters have even bother to attempt to explain why. Frankly, I'm not even certain... we see this from time to time with former-extratropical cyclones, likely due to cooler upper level temperatures (I've often talked about this and research done at MIT which shows that the often-ballyhooed 80F threshold is true only in the standard tropical environment, but cold epper level temps can lower that 80F threshold). But Epsilon has long since lost any extratropical remnant characteristics. May it still be cold aloft? Sure. And that may, indeed, be what's driving it. But it would be purely a guess to say this definitively. Otherwise, the story on Epsilon is bland and unchanged...

Current Conditions: Most recent satellite images as of Monday PM are finally beginning to show some decay. While surprisingly deep convection does remain in some quadrants, the entire southeastern quadrant of the eyewall has decayed and opened up. In fact, at 00Z the SAB Dvorak estimate just dipped down enough to bring Epsilon to a 55kt tropical storm. Given the gradations in the Dvorak technique, I'd say Epsilon remains very close to hurricane strength, but MAY be just below now... at about 60kts. As for motion, the satellite data and fixes indicate an almost due southeast motion now... at about 125 or 130 degrees at 7kts.

Model Discussion: With the current motion, clearly the more significant "looping" solutions appear to be on track. The models have, generally, responded to this. However, even though the larger loop moves Epsilon over warmer waters, the developing hostile upper level winds cause most of the models to still wipe the storm out quickly. For example, the NOGAPS, which had emphasized an eastward motion, now (00Z Tue run) has Epsilon looping S and even SWward, but, nonetheless, dissipates the storm by 72hrs (Thu). The 18Z GFS is actually extremely similar, showing a reasonably tight loop with dissipation by Thu afternoon. Almost amazingly, given the complexity of the situation, the 12Z ECMWF is in near perfect agreement... a modest curl and Thursday dissipation. The 12Z GFDL is *nearly* the same, except that it gets tripped up at the end... it's just a bit slower on the dissipation and, thus, allows Epsilon to rebound as conditions improve. The 12Z UKMET was not readily available, but the 00Z run mathced the other models well... showing a moderate loop (though the UK was a bit broader than some) with dissipation by Thursday morning.

My Thinking: Once again, difficult to say much. I'm not sure how I could possibly diverge from the models much at all. I would have been tempted to hold Epsilon together beyond Thursday, given its resiliency to date. But with Dvorak estimates now drifting down and the southeastern eyewall collapsing, I'm not so certain that it'll continue to be so resilient. So, I'll go for dissipation on Thursday. As for the track, while the situation is complex, the model agreement is strong and the loop is already begun. So, again, I'm just following the models on this... a clockwise loop through dissipation.



-Gary
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DISCLAIMER: All forecasts herein are made to the best ability of the forecaster. However, due to standard forecasting error, these forecasts cannot be guaranteed. Any action or inaction taken by users of this forecast is the sole responsibility of that user. **Re-publishing of this forecast text is prohibited except with consent of Gary Gray-Millennium Weather.