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Hurricane Lane Discussion Number  31
NWS Central Pacific Hurricane Center Honolulu HI   EP142018
1100 PM HST Tue Aug 21 2018
 
Lane remains an impressive hurricane this evening, with a well-
developed warm eye completely surrounded by persistent cold cloud 
tops. 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
this evening, shortly after the last forecast package, and found
winds within the northeast eyewall of 146 kt. Based on this
observation, a special forecast package was issued strengthening
Lane to a catagory 5 hurricane. Subjective Dvorak current intensity
estimates range from 6.5/127 kt (JTWC and SAB) to 7.0/140 kt (PHFO).
ADT from UW-CIMSS was 132 kt. Based on a blend of aircraft-observed
central pressures and wind speeds, we will set Lane's initial
intensity to 140 kt for this package. 

Initial motion for this advisory is 285/8 kt. Lane has been moving 
generally westward along the southern flank of a mid-level ridge 
during the past several days. However, this cyclone will soon begin 
to round the western periphery of this ridge and move into an area
of relatively light steering flow. This will allow Lane to gain
latitude as its forward speed diminishes. Lane is forecast to
continue moving west-northwest tonight, then turn to the northwest
on Wednesday, 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 13 kt of vertical shear now and this is forecast to
increase to 20 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 follows the previous one and lies between GFS and ECMWF
along FSSE.

Water temperatures along the forecast track will be 27 to 28
degrees C, warm enough to support a major hurricane. Any
significant weakening as Lane draws closer to the Hawaiian
Islands will likely be due to increasing wind shear. Through the
next 36 to 48 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, situated firmly between
the EMXI and IVCN ensemble guidance.


KEY MESSAGES: 

1. Lane is forecast to move dangerously close to the main Hawaiian 
Islands as a hurricane Thursday through Saturday, potentially 
bringing damaging winds and life-threatening flash flooding from 
heavy rainfall. As Lane is expected to be slow-moving as it nears 
the islands, it will produce large and damaging surf.
 
2. As Lane approaches the islands from the southeast, initial 
impacts will be felt on the Big Island, where a Hurricane Warning
is in effect. Preparations should be rushed to completion as
tropical-storm force winds are forecast to arrive by late Wednesday
or early Thursday. A Hurricane Watch remains in effect for Maui
County and the island of Oahu, with tropical-storm force winds
possibly beginning Thursday or Thursday night. 

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 impacts could be felt on any of the islands. 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  22/0900Z 14.7N 154.5W  140 KT 160 MPH
 12H  22/1800Z 15.4N 155.6W  135 KT 155 MPH
 24H  23/0600Z 16.6N 156.3W  125 KT 145 MPH
 36H  23/1800Z 17.8N 157.0W  110 KT 125 MPH
 48H  24/0600Z 19.1N 157.6W   95 KT 110 MPH
 72H  25/0600Z 21.0N 159.4W   70 KT  80 MPH
 96H  26/0600Z 21.2N 162.2W   50 KT  60 MPH
120H  27/0600Z 20.8N 165.3W   40 KT  45 MPH
 
$$
Forecaster Powell
 
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