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TROPICAL STORM DARBY DISCUSSION NUMBER  51
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI   EP052016
1100 PM HST SAT JUL 23 2016
 
Darby was difficult to find this evening after it emerged from the
Big Island. A 0732z ASCAT pass seems to confirm the current position
estimate. However, the system is likely continuing to organize after
its encounter with volcanic peaks of nearly 14 thousand feet,
earlier today. This terrain severely disrupted the low level center,
which appears to have emerged slightly south of its previous
forecast track. This is often the case with tropical cyclones that
encounter major land areas, especially when mountainous terrain
is present. In addition, the amount of time the center was over land
removed it from its primary energy source, which is the Pacific
Ocean. Since the center is again over water, all of the satellite
fix agencies estimated the current intensity to be 2.5/35 kt,
while the CIMSS ADT estimates was 2.3/33 kt. We are maintaining
Darby as a 35 kt tropical storm for this advisory.

The initial motion is estimated to be 290/09 kt, with the
poorly-defined center of Darby currently located just west
of the Big Island coast. The system is expected to eventually turn
toward the northwest, with Darby moving generally northwest through
the remainder of the forecast period. There remains some spread in
the track guidance, but the models continue to suggest this
northwest motion is likely to continue. The models appear to be
influenced by a forecast weakness developing in the mid-level ridge
to its north over the next 18 to 24 hours, due to a deep-layer low
that remain nearly stationary far north of the Hawaiian Islands.
The updated track forecast is close to the previous and closely
follows the latest multi-model consensus TVCN and the latest GFEX.
 
The intensity forecast is maintaining Darby as a minimal tropical
storm through 36 hours. The warm water temperatures and ample
ocean heat content depicted in the most recent CIRA analysis south
of the main Hawaiian Islands are likely sufficient to maintain a
tropical storm. The latest SHIPS guidance appears to indicate Darby
may not weaken as fast as it had in the previous run. However,
within 48 hours, all of the guidance indicates steady weakening will
occur, as increasing vertical wind shear and gradually cooling
waters lie along the forecast track. The latest forecast again
indicates weakening to a remnant low in 72 hours, with dissipation
expected by the end of the forecast period. 
 
Note that another flight by the 53rd Weather Reconnaissance Squadron
is scheduled to fly into Darby after dawn Sunday morning to
determine what the intensity of Darby is after its circulation
spends several more hours over the warm ocean waters west of the Big
Island. 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  24/0900Z 19.5N 156.8W   35 KT  40 MPH
 12H  24/1800Z 20.2N 157.8W   35 KT  40 MPH
 24H  25/0600Z 21.4N 159.1W   35 KT  40 MPH
 36H  25/1800Z 22.7N 160.6W   35 KT  40 MPH
 48H  26/0600Z 24.1N 162.1W   30 KT  35 MPH
 72H  27/0600Z 27.3N 165.2W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  28/0600Z 30.0N 169.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  29/0600Z...DISSIPATED
 
$$
Forecaster Houston
 
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