Darby Almost Done on the Big Island – Steady Weakening Anticipated

Tropical Storm Darby is beginning to move past the Big Island of Hawaii.

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A Tropical Storm Warning has been issued for Kauai County, including the islands of Kauai and Niihau.

Darby 723 5pm track

The 53rd Weather Reconnaissance Squadron flew through Darby for a good portion of the day, and departed the storm just before the poorly-defined center came ashore over the southeastern portion of the Big Island near Pahala around 2 pm.  The center is estimated to be traversing the southern slopes of the Big Island at this time.

Surface pressures were rising each time the plane sampled the system, and flight-level winds indicated that Darby’s intensity had weakened to near 35 kt, and that is the initial intensity for this advisory.  Another reconnaissance flight is scheduled for early Sunday morning to determine what remains of Darby’s circulation after it emerges from the Big Island.

The initial motion is estimated to be 275/09 kt, with the poorly-defined center of Darby currently estimated to be over interior portions of the Big Island.  After emerging from the Big Island later this evening, a turn toward the northwest is expected, with Darby moving toward the northwest through the remainder of the forecast period.

Darby is still expected to move into a weakness in the mid-level ridge to its north over the next 24 hours, as a deep-layer low remains nearly stationary far north of the Hawaiian Islands.

While the spread in the track guidance has increased slightly from the previous cycle, it continues to indicate a steady northwest motion.  The updated track forecast is close to the previous and the multi-model consensus TVCN.

As the center of Darby is currently over the Big Island, there is considerable uncertainty as to what will remain of the low-level circulation once it moves back over water later this evening.  The intensity forecast is conservatively maintaining Darby as a minimal tropical storm through 24 hours until it is clear that re-development will not occur.

Thereafter, steady weakening is anticipated, as increasing shear and gradually cooling waters lie along the forecast track.  The updated forecast indicates weakening to a remnant low in 72 hours, with dissipation expected by the end of the forecast period.  This is a slower rate of weakening than depicted by global models through the first 24 hours, and the intensity consensus, IVCN, but closely follows IVCN thereafter.

If Darby’s circulation does not survive its interaction with the Big Island’s rugged terrain, than dissipation will likely occur much sooner.

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