TS 'HILDA' is struggling this afternoon, local basin time, with persistant easterly shear, which is adversely affecting the system.
First off however, a bit of 'Historical Perspective' ...
Several strong bursts of deep convection overnight apparently overspread enough the LLCC to allow the system to become "Classifiable" as a Tropical Cyclone, and the nod was given to begin issueing advisories on TD-11E.
From the National Hurricane Center's First Discussion of the Developing Cyclone ...
>>"THE TROPICAL DISTURBANCE LOCATED ABOUT 1350 MILES EAST-SOUTHEAST OF THE HAWAIIAN ISLANDS HAS MAINTAINED A VIGOROUS CIRCULATION DURING THE LAST 24 HOURS...WITH PULSES OF DEEP CONVECTION COINCIDING WITH THE DIURNAL NOCTURNAL MAXIMUM.
MORE RECENTLY A DEEP CONVECTIVE CLUSTER HAS PERSISTED FOR SOME TIME OVER THE WESTERN SEMICIRCLE ... EVEN PARTIALLY COVERING WHAT WAS EARLIER AN EXPOSED CIRCULATION CENTER.
ADDITIONALLY...AN EXPANDING CIRRUS CANOPY IS EVIDENT IN SATELLITE IMAGERY...SUGGESTIVE OF A BETTER ESTABLISHED UPPER LEVEL OUTFLOW. SINCE THE DEEP CONVECTION HAS BEEN PERSISTENT AND THERE HAS BEEN A FURTHER INCREASE IN ORGANIZATION ... THIS SYSTEM CAN NOW BE CLASSIFIED AS A TROPICAL DEPRESSION.
BASED UPON DVORAK T-NUMBERS FROM TAFB AND SAB OF 2.0 AND AN EARLIER QUIKSCAT PASS...THE INITIAL INTENSITY (Of Depression 11E) IS SET AT 30 KT."
The Depression then deepened just a tad further, as indicated by a Quikscat Satellite Pass, to be officially tagged as "Tropical Storm HILDA".
From NHC's 2nd Forecast Discussion ...
>>"A (recent) QUIKSCAT PASS SHOWED A COUPLE OF BELIEVABLE 30-35 KT WINDS IMMEDIATELY TO THE NORTHEAST OF THE CIRCULATION CENTER ... SUGGESTING THAT THE SYSTEM WAS NEAR TROPICAL STORM STRENGTH AT THAT TIME.
DVORAK T-NUMBERS FROM TAFB AND SAB WERE AT 2.5 ... AND SERVE AS THE BASIS FOR THE INITIAL INTENSITY ESTIMATE ... WHICH IS SET AT 35 KTS."
And TD-11E was therefore 'Upgraded' to Tropical Storm "HILDA"
Since then however, HILDA has had a tough go of it. The diurnal convective minima, teaming up with the persistant easterly shear, has once again reduced the system to a *completely exposed* low level circulation center.
~ A Struggling Tropical Storm 'HILDA' with an Exposed Low Level Center ~
However! It should be noted that, as of this writing, there appears to be a strong banding feature developing in the NE quadrant of HILDA, and more significant, the persistant shear appears to be relaxing just a little, judging from the blowoffs in the developing rainband.
Additionally, if you look closely at the *last frame* of the visible animated satellite loop above, you will notice that deep convection is starting to fire again near the LLCC in the NW quadrant.
My surmise is that, with the approaching overnight 'Convective Max Cycle', in conjunction with the developing rainband off to the NE *and* a possible slight lessening of the NE Shear, we should see the deep convection overspreading the center-of-the-cyclone once again, possibly leading to an intensification phase of HILDA.
HILDA's Track appears to be guided by the Low/Mid Level Ridge, which will fluxuate in intensity over the next few days and induce a slightly more WNW'erly path and possibly slow the storm down a little ...
>>"... LARGE-SCALE MODELS SHOW THAT THE CYCLONE LIES TO THE SOUTH OF THE EASTERN EDGE OF A
SUBTROPICAL RIDGE OVER THE CENTRAL NORTH PACIFIC ... WHICH SHOULD STEER HILDA ON A GENERAL WESTERLY COURSE FOR THE NEXT FEW DAYS.
AROUND 72 HOURS...A DEEP MID- TO UPPER-LEVEL TROUGH IS FORECAST TO DIG SOUTHWARD ALONG 135W ... WHICH SHOULD TEMPORARILY WEAKEN THE SUBTROPICAL RIDGING NORTH OF HILDA.
AS A RESULT ... THE FORWARD SPEED OF THE CYCLONE SHOULD BEGIN TO SLOW IN A WEAKER DEEP-LAYER EASTERLY FLOW."
Although 'HILDA' is currently forecast to pass well to the south of the Hawaiian Islands in about a weeks' time, it is certainly worth watching closely, as the *amount and duration of the weakening* of the sub-tropical ridge to the north, and hence the upper-air steering currents, could very well change from what the current model guidance is suggesting at this time.
Another Advisory from the NHC is due out in less than an hour. Will update the situation and include a few more recent photos at that time.
Edited by CoconutCandy (Sat Aug 22 2009 10:46 PM)
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