Prognostic Meteorological Discussion
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FXHW01 KWNH 261216
PMDHI

Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
816 AM EDT Thu Apr 26 2018

Valid 00Z Fri Apr 27 2018 - 00Z Fri May 04 2018

A rapidly amplifying central Pacific trough aloft will close off
an upper low to the north of the state by Friday, reaching as far
south as 30-35N latitude by late Friday into the weekend.  The
upper low will begin to lift northeastward during the first half
of next week.  After early Monday heights over the island will
rise somewhat but a northeast-southwest trough should persist to
the north through midweek.

Developing low pressure associated with the upper low will anchor
a front that passes through the state from west to east during
Friday-Sunday.  There will be potential for some bands of locally
heavy rainfall along the front as deep moisture increases.  Trade
flow currently in place will become southeasterly ahead of the
front and northerly behind the front.  After Sunday the front and
axis of highest precipitable water values will remain close enough
to the Big Island, or perhaps lift back to the northwest a bit
given the rise in heights aloft, to support a heavy rainfall
threat at times over the eastern part of the state.  Differences
in location of the front/moisture axis as well as details aloft
are well within typical guidance error for 5-7 day forecasts and
at this time show no pronounced clustering.  Thus confidence in
any specific solution is not particularly high, recommending an
intermediate solution for forecast specifics.

The western islands should see a drier pattern next week with
relatively light windward showers.  Most guidance expects
west-central Pacific high pressure gradually building eastward to
promote a strengthening of northeasterly winds by next
Wednesday-Thursday.

Rausch

$$





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