Reconnaissance Squadron Returns with Data on Darby’s Strength, Size
Up to the minute TS Darby Updates are posted at the following link: http://mauinow.com/?p=205341
The 53rd Weather Reconnaissance Squadron has been flying through Darby all morning, providing valuable data as to Darby’s strength and size.
DARBY HAS WEAKENED SLIGHTLY: Maximum flight level winds near 50 kt indicate that Darby has weakened slightly since their visit last night, and the initial intensity for this advisory has been reduced to 40 kt.
POORLY DEFINED CENTER: The initial motion is estimated to be 280/09 kt, with the poorly-defined center of Darby located on the north side of the deep convection. Track guidance is fairly well clustered this time around, and continues to indicate that the center of Darby will move over the Big Island later today as it moves toward the west.
GRADUAL TURN TO THE NW, INCREASE IN FORWARD SPEED: Darby is expected to move into a weakness in the mid-level ridge to its north over the next day or so, due to a deep-layer low centered well to the north of the Hawaiian Islands. This will result in a gradual turn toward the northwest, as well as a gradual increase in forward speed. The official track forecast is close to the previous and a tightly clustered guidance suite, and offers no significant changes.
WATER VAPOR: As seen in water vapor imagery, Darby is embedded in an environment characterized by dry mid- and upper-levels, well captured by special soundings from Līhue and Hilo this morning.
WIND SHEAR: Additionally, vertical wind shear on the order of 10 to 15 kt is taking its toll on the system, and deep convection has been struggling to organize over the center.
DARBY TO REMAIN A TROPICAL STORM: The updated intensity forecast indicates that Darby will remain a tropical storm through 24 hours, after which time increasing shear and gradually cooling water temperatures will lead to a slow but steady weakening, with Darby becoming a remnant low at the end of the forecast period, close to guidance provided by SHIPS/LGEM.
ORGANIZATION UPON INTERACTION WITH BIG ISLAND TERRAIN: The intensity forecast assumes that Darby will be able to maintain some organization as it interacts with the terrain of the Big Island but no longer considers an alternative track scenario.
-Forecaster Birchard/NWS Central Pacific Hurricane Center