CoconutCandy
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Reged: Fri
Posts: 245
Loc: Beautiful Honolulu Hawaii
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Greetings all. Interesting turn of events.
Just as the northeasterly shear seemed like it was about to quash Boris, the diurnal convective maximum arrived, local basin time, and like the night before, Boris put out a pretty impressive convective burst.
Again, a large mesoscale convective complex, with extremely cold cloud tops of -80 and colder flared to the S and SE of the partially exposed LLC, and gradually these intense thunderstorms 'trained' towards the center, forming a large, kidney-bean shaped 'blob'. (See figure 1, below)
Just as one such event faded over several hours, another, even larger convective blast took it's place, even closer to a now less-exposed circulation center. And parallel bands of intense convection were stacked due south of the center, extending for hundreds of miles. (See figure 2)
Meanwhile, I was checking out some of the interesting microwave imagery from the superb website, and noticed something interesting.
While looking at the 0920Z Tropical Rainfall Measuring Mission (TRMM) satellite image, I noticed that the surface LLC (shallow cumulus and stratocumulus, shown as light blue on a brownish-green background) was slightly decoupled from a narrow 'convective ring' that was attempting to establish itself as the new intense convection trained and wrapped itself around center (narrow band of thunderstorms, shown as the bright red ring of precipitation). The offset seemed to be as much as 20 or 30 miles to the SSW. (See figure 3)
This is what is sometimes referred to as a de-coupling; when the mid-level and the low-level circulations are no longer vertically aligned. Taken to extremes, the thunderstorms become totally sheared off in one direction, while the LLC continues to chug along, becoming utterly devoid of any deep convection; a swirling pinwheel of only light showers. We've all seen this happen many times, a fairly common occurrence, and how many a cyclone has met it's early demise.
But! And here's where it gets interesting: Sometimes the shear will slacken a tad and/or the convection will, for whatever reason, tend to 'buck' the shear, and overtake and overspread what was an exposed LLC and re-establish a nice, vertically aligned column of deep convection, and wallah, the cyclone is granted a 2nd lease on life.
Well, such seems to be the case with Boris this morning. After putting on a very impressive convective burst all night, that activity is overspreading the LLC again, which seems to have re-invigorated Boris.
And a more recent, more complete, microwave pass continues to suggest Boris attempting to re-align itself in the vertical. (See figure 4) The time between the 2 microwave passes is only 22 minutes, so the convective 'ring' still appears to be displaced about 20-30 miles to the SSW of the apparent LLC.
Figure 1 - First large flareup of deep convection, forming 'kidney bean' shaped area.
Figure 2 - Second such flareup, about 6 hours later, after first one dissipated. NOTE also the small, circular 'eyewall-like' formation to the NW of the bigger convective mass. This is the pseudo-eyewall that clearly shows up in the passive microwave images in Figures 3 and 4 as the bright convective ring.
Figure 3 - The first microwave pass from the TRMM satellite, showing the bright red convective ring, located about 30 miles SSW of the LLC. Note that these two 'rings' are not that far apart; they actually overlap one another. See description accompanying next photo.
Figure 4 - The 2nd such pass from the AQUA-1 satellite, 22 minutes later, shows the 'loosely-coupled' cyclone better. If you look close, you can see the southernmost part of the LLC (light blue) through the middle of the red convective ring, *and* you can see the northern, weakest portion of the convective ring directly overlying the middle of the LLC. Essentially overlapping rings.
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As of this writing, no new microwave images have come in, so I can't be entirely sure, but just from looking and judging the IR loops, it sure seems to my untrained eye that the deep convection is not only persisting, but is completely overspreading the LLC. This intense activity is now developing a , or central dense overcast, usually an indicator of a deepening cyclone and a strengthening wind field.
The last few frames have shown a slight warming of the cloud tops, but this may be a reflection of the end of the diurnal convective maximum mentioned earlier, with the approach of the coming dawn, local basin time.
The storm is currently hugging the 27 C isotherm and the more stable air mass to it's N ans NW is not being ingested quite yet. So, beside the shear factor, it seems it's up to Boris if he can re-couple and re-align his mid and low level circulations, and live another day as a respectable tropical storm, and even maybe strengthen just a tad more. Next advisory out in about an hour from now.
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UPDATE: Latest advisory now out. is maintaining Boris at 45 Kts, but I still feel there's a small window of opportunity to strengthen some, especially since the shear appears to be letting up a little and outflow is improving in all quads. Even though the T numbers may not support it, I'll bet the Boris is currently stronger than indicated.
With this kind of sustained convective activity near the center and considering the improving outflow, how could it not strengthen? It all seems to depend on the whether Boris can successfully re-align it's circulation centers, before (a) the stable environment takes its toll, (b) the shear collapses the now partially aligned center, or (c) the system slows to a crawl and is eventually ingested by the much larger cyclonic circulation forming to its east.
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This should be interesting to see how it plays out. The and HWFR models do strengthen Boris in the near-term, but admittedly, they are the 'outliers'.
Will the coming convective minimum and the NE-erly shear conspire together to send Boris to his demise, or will he maintain his tenacity in the face of adversity?
I'm putting my bets that Boris will put on one last hurrah and surprise the nay-sayers. Any takers ??
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CoconutCandy
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Reged: Fri
Posts: 245
Loc: Beautiful Honolulu Hawaii
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What a fun and interesting ride this has been. My intuition proves to be correct once again!
Just as I had expected, this tropical storm has managed to buck the persistent 20 Kt. ENE shear and, with the convective trends observed earlier continuing unabated, Boris seems to have almost completely re-coupled his lower and upper level circulations and now borders on hurricane strength. There are already hurricane force gusts to 75 Kts. 
Quote:
"THE SYSTEM IS WITHSTANDING ABOUT 20 KT OF ENE SHEAR ON THE S SIDE OF A STRONG UPPER LEVEL HIGH...BUT IS STILL EMBEDDED WITHIN AN UNSTABLE MOISTURE-LADEN ENVIRONMENT."
It's this 'unstable, moisture-laden environment' that was so conducive for the large convective blowups observed last night and have continued all day to sporadically flare up, drawing in enormous quantities of high-CAPE air (Convective Available Potential Energy) from hundreds of miles to it's south.
It's this high CAPE, moisture-laden air that resulted in the formation of a mid-level 'convective ring' that was observed from passive microwave imaging satellites beginning around --Z last night. (See figures 3 and 4, previous post)
And successive microwave imaging passes throughout the day have continued to depict a very healthy mid-level 'precipitation ring', all the while the LLC is slowly being drawn towards the center of lowest pressure, now relocating under the intensifying mid-level circulation.
In essence, Boris has managed to almost completely recouple and vertically realign his lower and upper level circulations, and all the tremendous release of latent heat of condensation from all that unstable, high-CAPE inflow has finally worked it's way to the surface, resulting in pressures dropping 8 millibars and winds increasing 15 Kts.
But make no mistake: Boris did not suddenly go from 45 Kts. to 60 Kts. at the drop of a hat, nor did pressures drop 8 mb at the click of the second hand.
Here's the rub. It's my contention that Boris had been steadily strengthening all day with pressures steadily dropping, too, despite 's continuing insistance on using solely T numbers for their intensity estimates.
As it turns out, T number estimates are very 'sensitive' to the center of the LLC. If the 'estimated' center of the LLC is 'off' by as little as 20 or 30 miles, this can have an effect of 1 or 2 T number values, quite possibly resulting in a stronger or weaker storm than what is provided in the advisory issued.
This seems to be the case with Boris throughout today (Sunday). The forecasters at the apparently gave little thought about the possibility of the storm slowly recoupling, insisting on the LLC being too far displaced from the strengthening mid-level circulation.
Even the 21Z advisory, despite having several hours of visible satellite loops to observe, the forecasters apparently still did not realize that the cyclone was recoupling. I was rather surprised. What was so obvious to me was either unnoticed or misintrepreted by the forecasters.
Finally, a special advisory was issued 3 hours later, after it was 'just too obvious' that there was a cloudy, ragged eye forming on visible loops.
Quote:
"THE PURPOSE OF THIS SPECIAL ADVISORY IS TO INCREASE THE INITIAL AND FORECAST INTENSITIES OF BORIS. OVER THE PAST COUPLE OF HOURS...A RAGGED EYE HAS BEEN APPARENT IN VISIBLE SATELLITE IMAGERY.
IN ADDITION...A RECENT MICROWAVE PASS INDICATES THAT THE LOW-LEVEL CENTER OF BORIS IS REASONABLY CO-LOCATED WITH THE VISIBLE EYE FEATURE. THE CIMSS ADT ESTIMATES THE INTENSITY OF THE CYCLONE TO BE JUST BELOW HURRICANE STRENGTH. AS A RESULT...THE ADVISORY INTENSITY IS INCREASED TO 60 KT."
Boris was very likely already stronger than 45 Kts. in the hours preceding this special advisory. It *certainly* appeared that way from careful inspection of the visible loops.
I guess it took the presence of the 'ragged eye' formation to really get their attention and realize that just maybe Boris was in the process of recoupling. Finally, the 'recent microwave pass' then forced their hand to issue the special advisory.
From the most recent advisory as of the time of this writing ...
Quote:
"THE RAGGED EYE VISIBLE EARLIER HAS BEEN OBSCURED BY NEW CONVECTION NEAR THE CENTER ... ALTHOUGH EXCELLENT BANDING ALOFT IS APPARENT IN AN AMSU PASS.
THE MICROWAVE IMAGERY IS NOT CONCLUSIVE BUT SUGGESTS A SMALL DISLOCATION OF THE SURFACE AND UPPER CENTERS...IN LINE WITH THE MODEST NORTHEASTERLY SHEAR STILL AFFECTING THE CYCLONE. ALL OF THE OBJECTIVE GUIDANCE ... INDICATE A LITTLE MORE STRENGTHING WHILE THE CYCLONE IS (still) OVER 27C WATERS..."
So, let's wrap up here. As it turns out, after watching developments overnight and throughout today, especially with regard to the possibility of a re-coupling of the circulation centers, it actually has happened!
Boris did indeed realign in the vertical and strengthen from a mediocre 45 Kt. storm with a partially exposed LLC, to a vigorous cyclone bordering on hurricane intensity (blowing a hurricane in gusts!) with a ragged eyewall forming and visible for several hours.
The point I'm really trying to make here is that, despite all our great numerical modeling tools, and subjective analysis tools like the T number technique, good 'ol mother nature can and sometimes does throw us that proverbial curveball, just when the models (and forecasters!) were expecting the slider.
And the point I'd like to make in closing is that peak intensity estimates for EastPac storms, especially, tend to be too conservative, as I've already mentioned. I've watched this basin for the better part of 3 decades, and have seen this time and time again. Or dramatic regeneration of systems when 'absolutely' none was expected. That kind of thing.
The Eastern Pacific, being the 2nd most active basin in the world (after the WestPac's Typhoons) is *also* the most data-sparse of all the basins. Thanks goodness for all our remote sensing satellites to keep tabs from space. But even with them at our aid, unexpected changes can and do sometimes happen.
The tools can only be as good as the forecasters' accurate and timely interpretation of their data !! 
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