5AM Hurricane Lane Update & Discussion

At 500 AM HST (1500 UTC), the center of Hurricane Lane was located
near latitude 15.1 North, longitude 155.3 West. Lane is moving
toward the west-northwest near 9 mph (15 km/h) and this motion is
expected to become northwest later today, followed by a
turn to the north-northwest on Thursday. On the forecast track, the
center of Lane will move very close to or over the main Hawaiian
Islands from Thursday through Saturday.
 
Maximum sustained winds are near 155 mph (250 km/h) with higher
gusts.  Lane is a category 4 hurricane on the Saffir-Simpson
Hurricane Wind Scale.  Some weakening is forecast during the next 48
hours,  but Lane is forecast to remain a dangerous hurricane as it
draws closer to the Hawaiian Islands.
 
Hurricane-force winds extend outward up to 40 miles (65 km) from the
center and tropical-storm-force winds extend outward up to 140 miles
(220 km).

500 AM HST Wed Aug 22 2018

A bit of asymmetry within the coldest cloud tops is now noticeable,
but Lane remains a well-organized hurricane this morning. Outflow
remains best to the north through east and is slightly restricted
elsewhere. Hurricane Hunter aircraft from the 53rd Weather
Reconnaissance Squadron flew through Lane once again overnight,
deriving 130 kt within the northeast eyewall (using a blend of
observations). Subjective Dvorak current intensity estimates were
6.5/127 kt from all three centers. ADT from UW-CIMSS was also
6.5/127 kt. Initial intensity is set at 135 kt for this advisory,
which is slightly lower than for the last advisory.

Initial motion for this advisory is 290/8 kt. Lane has likely
reached the western periphery of a mid-level ridge and has made its
anticipated turn toward the west northwest. Lane is forecast to
turn to the northwest later today, and to the north-northwest on
Thursday, as it moves between the mid-level ridge to the east and a
developing upper-level trough to the northwest of Hawaii. The track
and intensity forecasts become increasingly uncertain after this
point as most track guidance brings Lane very close to the islands,
with potential interaction between Lane and the mountainous terrain
of the islands. UW-CIMMS derives 15 kt of vertical shear now and
this is forecast to increase to 25 to 30 kt at 48 hours, according
to ECMWF SHIPS. The combination of land interaction and increasing
vertical shear leads to a weakened Lane being steered to the west by
the low-level trade wind flow during the later forecast periods. The
new track forecast closely resembles the previous one and follows
HCCA and TVCE between GFS and ECMWF. A slight bump to the left was
made through 36 hours to account for initial motion, while a slight
bump to the right was made to keep the track within the guidance
envelop at 48 and 72 hours.

Water temperatures along the forecast track will be 27 to 28
degrees C, warm enough to support a major hurricane. Therefore, any
significant weakening as Lane draws closer to the Hawaiian Islands
will likely be due to increasing wind shear. Through the next 36
hours, shear is expected to remain in the 10 to 20 kt range, and we
expect only slow weakening initially. At 48 hours and beyond, the
forecast incorporates an expected sharp increase in shear as Lane
moves closer to the large upper trough to the northwest of the main
Hawaiian Islands. The new intensity forecast is very similar to the
previous forecast and lies near the top of the guidance envelope
but not too far from HMNI and IVCN.

KEY MESSAGES:

1. Lane is forecast to move dangerously close to the main Hawaiian
Islands as a hurricane tomorrow through Saturday, potentially
bringing damaging winds and life-threatening flash flooding from
heavy rainfall. As Lane will be slow-moving as it nears the
islands, large and damaging surf can be expected along exposed
shorelines, along with localized storm surge.

2. As Lane approaches the islands from the southeast, initial
impacts will be felt on the Big Island and Maui County, where a
Hurricane Warning is in effect. Impacts on Kauai County and Oahu
are also possible, and a Hurricane Watch is in effect there.

3. Do not focus on the exact forecast track for Lane, as life-
threatening weather conditions extend well away from the center of
the hurricane, and significant impacts could be felt on any of the
islands.

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