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Reged: Fri
Posts: 245
Loc: Beautiful Honolulu Hawaii
Hurricane Boris Maintains It's Eyewall
      #80224 - Wed Jul 02 2008 01:11 PM

Boris continues to evade his demise, and put on his last big final hurrah during last night's diurnal convective max cycle. He's taken on an almost annular appearance.

The past 3 or 4 advisories called for a drop to TS classification, but despite increasingly cooler SST's and gradually approaching a more stable air mass, Boris held onto minimal hurricane status when steady weakening was forecast.

It actually improved it's upper warm core dynamics, which reflected in a much improved eyewall signature, as shown on successive microwave overpasses and the visually arresting IR loops, displaying a nice clear eye of ever increasing diameter.

And despite crossing over several isotherms in quick succession, venturing well outside the 26 C threshold, the eyewall dynamics continued to improve, with a new complete unbroken eyewall observed in a recent microwave pass.

Since then, the eyewall is beginning to look a little ragged and broken again, and the nice clear eye is beginning to fill in with clouds; the harbinger of things to come.

Boris took an unexpected (previously not forecast) excursion to the NW over the past 12-18 hours, it's eyewall apparently sensing a temporary weakness in the subtropical ridge to it's north. But the ridge is now rebuilding, returning the storm to a more westerly track with time.

Boris, now over 24C and cooler waters, has spent his last hurrah sporting a pretty decent looking classic hurricane structure, if not exactly huge in size.

But! Not too shabby for a cyclone that was initially expected to peak as a 35 Kt. storm and was nearly always 'under-forecast' with regard to 'current intensity estimates' (IMHO), and especially, (no opinion needed here), in intensity forecasts 1-3 days out.

The likely fuel for Boris' final performance was a massive fetch of highly unstable and very moist air, drawing up the ITCZ like a huge spiral rainband structure in the SE semicircle.

Although never actually merging into the inner eyewall dynamics, one cannot help but think that it was of major significance by infusing the vast cyclonic circulation with enormous quantities of 'fuel rich' air, or what's know as high "theta-e" with high "convective available potential energy". The kind of stuff that hurricanes love to snack on.

Finally, it's interesting to note that, now that the cyclone is over cooler waters, the inner eyewall convection is not *quite* as intense (deep) as was the case the past few days.

It's now managing only -70 C, at best, and continuing to warm by the hour, especially now that day has dawned, local basin time, and the diurnal max is over. Compared with the intense convection of TD 4E, which is approaching and exceeding -90 (!), Boris looks pale by comparison.

It really illustrates how convective intensity is utterly dependent on SST. Fun things to watch and understand as they unfold before your very eyes.

More later when I can find the time.

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Reged: Fri
Posts: 245
Loc: Beautiful Honolulu Hawaii
Re: Hurricane Boris Maintains It's Eyewall [Re: CoconutCandy]
      #80226 - Wed Jul 02 2008 01:36 PM

Quick Update.

A couple microwave passes just in now show the eyewall to be open in the SE semicircle. But still quite impressive in the NW.

And daylight visible loops show the eye becoming diffuse and cloud filled. Seems that Boris has paid dearly for his eyewall extravagances of last night. Cannot fool mother nature, or cooler SST's !!

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