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Tropical Storm Akoni Discussion Number   8
NWS Central Pacific Hurricane Center Honolulu HI   EP122019
500 PM HST Thu Sep 05 2019
 
Akoni remains a very messy tropical cyclone embedded within the
intertropical convergence zone (ITCZ). Although an earlier ASCAT-C
pass revealed some 40 kt winds within a burst of deep convection,
that burst has since faded, leaving a large amorphous blob of cloud
with only a few small pockets of deep convection and no appreciable
banding features. Subjective satellite intensity estimates ranged
from 2.0 at PHFO to 2.5 at JTWC and SAB, while CIMSS-ADT was giving
3.5. We have elected to maintain the intensity at 40 kt for now.
Both the initial position and current intensity remain quite
uncertain. 

The initial motion of the overall cloud system is estimated to be
270/8. As difficult as it is to find the center of Akoni, the
guidance is in remarkably good agreement about where it will go
over the next few days. A strengthening deep layer ridge far to
the north of the main Hawaiian Islands will bridge westward along
latitude 32N, which will keep Akoni on a westward to west-
northwestward track the next several days. The challenges with
estimating the initial position have necessitated a slight westward
nudge in the official track, which remains near the tightly packed 
consensus guidance.

The intensity forecast remains challenging and fairly uncertain.
Deep convection associated with the ITCZ and the presence of
nearby dry air may continue to provide some disruptive effects on
the low level circulation center. The UW-CIMSS shear analysis is
also indicating 15 to 20 kt of westerly shear which may persist for
another 12 to 24 hours. If Akoni can seperate from the ITCZ,
conditions seem at least marginally favorable for strengthening,
with warm sea surface temperatures, and relatively weak shear in
the 24 to 60 hour timeframe. Shear will increase in the day 3 to 5
timeframe, which should begin to induce some weakening by the end
of the forecast period. Our intensity forecast lies on the
conservative side of the guidance envelope.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  06/0300Z 11.7N 145.7W   40 KT  45 MPH
 12H  06/1200Z 11.6N 146.8W   40 KT  45 MPH
 24H  07/0000Z 11.8N 148.5W   45 KT  50 MPH
 36H  07/1200Z 12.0N 150.6W   45 KT  50 MPH
 48H  08/0000Z 12.4N 153.0W   45 KT  50 MPH
 72H  09/0000Z 14.1N 159.2W   50 KT  60 MPH
 96H  10/0000Z 16.1N 166.1W   55 KT  65 MPH
120H  11/0000Z 17.7N 171.7W   50 KT  60 MPH
 
$$
Forecaster Ballard
 
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