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Tropical Depression Flossie Discussion Number  31
NWS Central Pacific Hurricane Center Honolulu HI   EP072019
500 PM HST Sun Aug 04 2019
 
Deep convection in the northeast quadrant of Flossie collapsed
around 1800 UTC due to westerly vertical wind shear in excess of 20
kt. Since then, the low-level circulation center (LLCC) has been
completely exposed, and isolated convection has been displaced
over 175 nm to the east. Subjective Dvorak current intensity
estimates ranged from a 1.5/25 kt from SAB to 2.0/30 kt from JTWC to
2.5/35 kt from HFO, while data T numbers were all lower. Based on
these inputs and the absence of central convection for more than six
hours, the initial intensity is lowered to 30 kt, and Flossie is now
a tropical depression.

The exposed LLCC of the depression is moving toward the west (270
degrees) at 11 kt. The continued westward motion, which will persist
into Monday, gives increased confidence that the weakening system is
becoming shallow and under a greater steering influence from the
low- to mid-level ridge to the north. As the ridge weakens, Flossie
is forecast to turn toward the west-northwest late Monday and remain
on that motion near or over the main Hawaiian Islands until
dissipation. The forecast track is nudged slightly south from the
prior advisory and remains close to the ECMWF and HWRF near the
middle of the guidance envelope. 

Flossie will gradually spin down over the next couple of days. An
upper-level trough northwest of Hawaii will remain in place during
this time, maintaining strong west-southwest winds aloft. As Flossie
moves westward under these strong upper-level winds, vertical wind
shear will increase to 30 to 40 kt tonight and Monday, causing
the depression to slowly weaken as it moves near or over the
Hawaiian Islands. The forecast is in line with the dynamical and
statistical guidance but keeps Flossie slightly stronger than nearly
all guidance in the next 12 to 24 hours.

Interests in the main Hawaiian Islands should refer to products
issued by the National Weather Service in Honolulu for information
on flooding and surf impacts from Tropical Depression Flossie.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  05/0300Z 18.9N 149.8W   30 KT  35 MPH
 12H  05/1200Z 19.1N 151.8W   30 KT  35 MPH
 24H  06/0000Z 19.8N 154.4W   30 KT  35 MPH
 36H  06/1200Z 20.8N 156.7W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  07/0000Z 21.8N 158.3W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  08/0000Z...DISSIPATED
 
$$
Forecaster Wroe
 
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