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Hurricane Lane Discussion Number  36
NWS Central Pacific Hurricane Center Honolulu HI   EP142018
500 AM HST Thu Aug 23 2018


Lane's satellite appearance has degraded somewhat since the previous
advisory as southwesterly shear impacts the vertical integrity of
the cyclone. However, the eye is still evident in traditional
infrared imagery and remains surrounded by a solid ring of cold
cloud tops. Water vapor imagery shows Lane's circulation
becoming elongated, with outflow severely restricted in the
southwest semicircle. The subjective Dvorak current intensity
estimates from GTW/TAFB/HFO/SAB ranged from 6.0/115 kt to 6.5/127 kt
for this advisory, while data-T numbers were as low as 5.5/105 kt.
Using a blend, the initial intensity for this advisory is set at 115
kt. 

Lane is currently moving toward the northwest into an increasingly 
hostile environment between a deep-layer ridge to the east, and a 
trough aloft to the northwest. The initial motion for this advisory 
is 320/6 kt, with southwesterly shear estimated to be around
25 kt by UW-CIMSS. 

The track and intensity forecast are extremely dependent on one 
another in the current forecast scenario, with Lane expected to
move generally toward the north while it remains a hurricane, and 
generally toward the west once it weakens. Confidence in the 
forecast is reduced because it is uncertain how Lane's core will be 
impacted by its potential interaction with island terrain, and the 
subsequent rate of weakening. Regardless of whether Lane's center 
moves over one of the Hawaiian Islands, an increasing amount of 
southwesterly shear along the forecast track will lead to 
significant weakening. If Lane's core were to move over one of the 
islands as has been consistently depicted by GFS/HWRF, then the 
cyclone would weaken even more rapidly. EMX2 is on the left side of 
the guidance and indicates less interaction with island terrain,
and therefore a slightly slower rate of weakening. 

Based on a preponderance of evidence presented by the guidance, the 
updated forecast indicates a faster rate of weakening than
indicated earlier, especially on days 2 and 3. The expectation is
that Lane will weaken due to the combined and cumulative effects of 
debilitating shear and the interruption of the circulation due to 
proximity to the high mountains of Maui and the Big Island. The 
official intensity forecast now closely follows IVCN, SHIPS and the 
ECMWF-based SHIPS. The track forecast anticipates this weakening, 
with Lane turning sharply toward the west on day 3. Until then, the 
forecast track is shifted slightly to the right of the previous 
forecast through Friday, bringing Lane northward and very close to
the Big Island and Maui County. This is similar to the multi-model
consensus HCCA, which includes GFS and HWRF as weighted members. A
slow forward speed is expected as this occurs, with Lane then moving
more quickly toward west as it becomes shallow and carried by the
low-level trade wind flow. 

NOAA Buoy 51002 to the southwest of the islands is in the path of
Lane, and recently reported a wind gust to 56 kt and significant
wave heights near 23 ft. Associated data were used to refine wind
and seas radii in the northwest quadrant. 


KEY MESSAGES: 

1. Lane will pass dangerously close to the main Hawaiian Islands as 
a hurricane today and Friday, and is expected to bring damaging 
winds. These winds can be accelerated over and downslope from
elevated terrain, and will be higher in high rise buildings.

2. The slow movement of Lane also greatly increases the threat for 
prolonged heavy rainfall and extreme rainfall totals. This is 
expected to lead to life-threatening flash flooding and landslides 
over all Hawaiian Islands. 

3. Large and damaging surf can be expected along exposed
shorelines, especially along south and west facing coasts, with
localized storm surge exacerbating the impacts of a prolonged period
of damaging surf.
 
4. Do not focus on the exact forecast track or intensity of Lane, 
and be prepared for adjustments to the forecast. Although the 
official forecast does not explicitly indicate Lane's center making 
landfall over any of the islands, this could still occur. Even if 
the center of Lane remains offshore, severe impacts could still be 
realized as they extend well away from the center.  
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  23/1500Z 16.9N 157.4W  115 KT 130 MPH
 12H  24/0000Z 17.9N 157.5W  105 KT 120 MPH
 24H  24/1200Z 19.1N 157.6W   95 KT 110 MPH
 36H  25/0000Z 20.0N 157.8W   75 KT  85 MPH
 48H  25/1200Z 20.3N 158.6W   60 KT  70 MPH
 72H  26/1200Z 20.0N 161.3W   45 KT  50 MPH
 96H  27/1200Z 20.0N 164.0W   40 KT  45 MPH
120H  28/1200Z 21.5N 166.0W   40 KT  45 MPH
 
$$
Forecaster Birchard
 
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