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Hurricane MIRIAM


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Hurricane Miriam Discussion Number  17
NWS Central Pacific Hurricane Center Honolulu HI   EP152018
1100 PM HST Wed Aug 29 2018
 
The satellite presentation of Miriam has improved slightly since
the previous advisory, with deep convection remaining over the
difficult to locate low level circulation center. The latest
subjective Dvorak intensity estimates from PHFO, SAB and JTWC ranged
from 4.0 (65 knots) to 4.5 (77 knots) while the Advanced Dvorak
Technique from UW-CIMSS came in at 3.5 (55 knots). Since the
satellite presentation has improved slightly since the previous
advisory, the initial intensity will be increased to 70 knots with
this advisory, which correlates well with a blend of the intensity
estimates. The initial motion is set at 300/07 knots.

Miriam is being steered by a large subtropical ridge to the 
northeast of the system and a deep mid-upper level trough to the 
north-northwest. Miriam is expected to track off to the northwest 
tonight then make a turn toward the north Thursday through Friday 
night. The increasing west-southwesterly shear should result in a 
decoupling of the system by early Saturday, and this is expected to 
result in a turn toward the northwest and eventually west Saturday 
through Monday as Miriam becomes influenced primarily by the low 
level trade wind flow. The official forecast for this advisory is 
nearly identical to the previous advisory and closely follows the 
consensus guidance.

The environment will be conducive for additional intensification of 
Miriam over the next 24 hours, with shear values remaining low, sea 
surface temperatures holding around 28C, while the system moves
over a region of higher Ocean Heat Content. As a result the
official forecast calls for slight intensification over the next 24
hours, followed by slow and steady weakening between 24 and 36
hours as Miriam begins to feel the effects of strengthening west-
southwesterly shear. Beyond 36 hours the intensity forecast will 
show fairly rapid weakening as shear values increase into the 30 to 
45 knot range, while the system moves over marginal sea surface 
temperatures of 26C or below.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  30/0900Z 14.7N 141.1W   70 KT  80 MPH
 12H  30/1800Z 15.4N 141.6W   75 KT  85 MPH
 24H  31/0600Z 16.8N 141.6W   80 KT  90 MPH
 36H  31/1800Z 18.4N 141.5W   70 KT  80 MPH
 48H  01/0600Z 19.9N 141.9W   55 KT  65 MPH
 72H  02/0600Z 23.0N 144.0W   40 KT  45 MPH
 96H  03/0600Z 25.5N 147.5W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  04/0600Z 27.0N 152.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster Jelsema
 
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