1. An area of showers and thunderstorms is associated with a
disturbance around 700 miles southeast of Hilo, Hawaii. Conditions
are only marginally favorable for development of this disturbance
over the next several days.
* Formation chance through 48 hours...low...20 percent
* Formation chance through 5 days...low...20 percent
Tropical Storm Akoni Special Discussion Number 7
NWS Central Pacific Hurricane Center Honolulu HI EP122019
100 PM HST Thu Sep 05 2019
An ASCAT-C pass from 1843 UTC revealed tropical storm force winds in
the vigorous deep convection blowing up to the east and southeast of
the low-level circulation center. Thus, this special advisory
upgrades TD 12E to Tropical Storm Akoni. The remainder of the
forecast philosophy does not change with this update, however the
intensity forecast was nudged upward in the short term to better
agree with the analyzed current intensity. Akoni remains a very
asymmetric and disorganized system, but is expected to gradually
intensify over the next few days.
Tropical Depression Twelve-E Discussion Number 2...Correction
NWS Central Pacific Hurricane Center Honolulu HI EP122019
1100 AM HST Wed Sep 04 2019
The earlier burst of convection over TD 12E has faded, leaving a
rather ragged and elliptical looking system. Recent ASCAT data, the
subjective intensity estimates from PHFO, SAB, and JTWC, and the
UW-CIMSS ADT all suggest maintaining the depression at 25 kt.
It should be noted there is considerable uncertainty in the initial
position owing to the poor organization of the system currently.
The relatively shallow nature of the circulation is resulting in an
initial motion of about 255/8, as the depression is being steered
by relatively weak low level trade wind flow. Guidance is in good
agreement that a gradual turn toward due west is expected in a
couple of days, with a turn toward the west-northwest thereafter
along with an increase in speed as the system moves south of
stronger, deep subtropical ridging. There was a slight southward
shift in the consensus guidance for this forecast, so the official
track has been nudged a little to the south as well. Toward the end
of the forecast period, the system should start to move more quickly
toward a weakness that develops in the subtropical ridge north
of the Northwest Hawaiian Islands.
Sea surface temperatures are above 28C along the forecast track of
12E and shear is relatively weak. The main inhibiting factor in the
short term appears to be the poor organization and shape of the
circulation, as well as some dry air impinging on the northern
periphery of the circulation. The guidance suggests gradual
strenghtening, and the official forecast does as well assuming the
depression can overcome the inhibiting factors. The official
forecast splits the difference between the slightly more aggressive
SHIPS guidance and the somewhat less agressive dynamical model
guidance.
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