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Hurricane Miriam Discussion Number 16
NWS Central Pacific Hurricane Center Honolulu HI EP152018
500 PM HST Wed Aug 29 2018
While cloud tops associated with Miriam were on general warming
trend since the previous advisory, a new burst of convection has
recently developed over the center, while organized convective
bands continue to wrap in to the center from the southeast.
Subjective Dvorak intensity estimates of 4.0/65 kt from SAB/HFO are
supported by UW-CIMSS ADT, and that will be the initial intensity
estimate for this advisory.
The initial motion estimate is a somewhat uncertain 280/7 kt, as
the low-level center has been difficult to identify. Miriam has
moved into an area of light steering flow between a mid-level ridge
centered over the southwestern U.S., and a mid- to upper-level low
centered northeast of Hawaii. The gradient between the low and the
ridge will result in a southerly steering flow that will take
Miriam toward the north the next couple of days. A turn toward the
northwest is expected to begin tonight, followed by a turn toward
the north on Thursday, with the dynamical models in good agreement
on this evolution. Increasing model spread persists after day 3,
with ECMWF taking a deeper cyclone much faster and farther
northward than the most of the guidance, with this solution taking
consensus members well to the right of the updated forecast track.
The official forecast continues to lean toward the GFS and its
ensemble solution, with Miriam turning west-northwestward toward the
end of the forecast period as a weak and shallow system primarily
steered by the low-level trade wind flow.
The forecast anticipates that Miriam will be in an environment
conducive for modest strengthening for the next 24 hours or so,
with shear near 10 kt and SSTs near 28C. The forecast track toward
the north will take Miriam over cooler waters thereafter, with SSTs
below 26C by 72 h. Southwesterly shear is expected to increase to
near 30 kt in 48 h and to 40 kt in 72 h, and Miriam is expected to
degenerate into a remnant low by day 4. The official intensity
forecast follows trends presented by the multi-model consensus and
SHIPS.
FORECAST POSITIONS AND MAX WINDS
INIT 30/0300Z 14.4N 140.6W 65 KT 75 MPH
12H 30/1200Z 14.8N 141.2W 70 KT 80 MPH
24H 31/0000Z 16.0N 141.6W 75 KT 85 MPH
36H 31/1200Z 17.7N 141.5W 65 KT 75 MPH
48H 01/0000Z 19.4N 141.6W 55 KT 65 MPH
72H 02/0000Z 22.0N 143.2W 40 KT 45 MPH
96H 03/0000Z 25.0N 147.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 04/0000Z 27.0N 151.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
$$
Forecaster Birchard
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