Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
725 AM EST Thu Feb 23 2017

Valid 00Z Fri Feb 24 2017 - 00Z Fri Mar 03 2017

Models are initially in good agreement, showing a Rex block
persisting north of the Hawaiian Islands initially before
beginning to break down by Monday. A couple upper lows south of
the ridge along 35N will not have a significant affect on Hawai'i,
with surface winds generally ENE around 20kt and becoming lighter
through the weekend. Precipitable water values will be relatively
low through Saturday (less than 1 inch) but are then forecast to
gradually increase from Sunday onward was 850 hPa flow begins to
turn southeasterly.

The most significant feature of note is a potential surface low
which a number of models develop and move near of east of the
Islands by the middle of next week. This appears to originate with
a disturbance in the zonal flow near 30N 140E today. The 00z
GEFS/ECMWF ensemble means as well as the deterministic runs are in
general agreement that this wave will amplify as it moves south of
the upper low northwest of the Hawai'i Sunday and Monday.
Model/ensemble agreement is also generally high with bringing this
wave to the Hawaiian Islands by Tuesday. Differences emerge with
the exact surface evolution that results from the wave. The 00z
GFS and CMC both develop stronger surface lows relative to the
ECMWF. The GFS takes the low from southwest to northeast, east of
the Big Island on Tuesday, with support from the GEFS and the
NAEFS. The 00z ECMWF shows a weaker low that the central Hawaiian
Islands on Wednesday. Given a broad area of convection south of
the Islands prior to the low development, the GFS solution appears
to be suffering from some convective feedback which may result in
a stronger low - although warm SST anomalies southeast of the
Islands may support more rapid low development. Nonetheless, there
is the potential for a period of stronger low-level E-SE flow and
potentially heavy rain by Tues-Wed next week, especially over the
eastern Hawaiian Islands. Surface winds could potentially turn
southwesterly Wed or Thur in the wake of the system.


Ryan/Roth