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FXHW01 KWNH 100758

PMDHI 



Hawaii Extended Forecast Discussion

NWS Weather Prediction Center College Park MD

358 AM EDT Wed Apr 10 2024



Valid 00Z Thu Apr 11 2024 - 00Z Thu Apr 18 2024



Latest guidance is consistent in showing an upper low closing off

to the northwest of the state during the day Wednesday, followed

by a north-northeast drift by the weekend when it should open up

as energy to the north/northwest reinforces mean troughing with

another embedded low.  There is a fair amount of spread for the

exact details of the southern part of the trough from the weekend

into next week. The initial upper low will support a corresponding

surface low and a front/convergence axis that extends southward

just to the west of the main islands.  This pattern will lift

abundant moisture northward, with even the ensemble means showing

precipitable water values reaching at least three standard

deviations above climatology for a time between Thursday and the

weekend.  Dynamical and machine-learning guidance is fairly

similar in principle with the surface feature helping to focus an

axis of potentially heavy rainfall that may affect Kauai and

vicinity Thursday onward, possibly nudging westward a bit for a

time.  Then gradual progression of the upper trough should begin

to push the front eastward, with enhanced precipitation extending

into the western half or so of the islands by Sunday-Monday. 

After that time, some moisture/rainfall may reach farther eastward

but with lesser totals as precipitable water values decrease. 

More pronounced drying may reach into the western islands.



As for guidance comparisons, the 00Z CMC strays from most other

guidance with a farther east upper trough and surface reflection

from the weekend onward.  Remaining dynamical guidance and

machine-learning models do not agree well for the exact character

of upper troughing to the north and embedded upper low position

from late Sunday onward.  Recent GFS runs are farthest south with

the second upper low versus other dynamical models/means (though

the 00Z GFS is less extreme than the 18Z run) while recent

machine-learning models have varied considerably for details to

the north of the state.  Therefore confidence in specifics for the

front moving into the islands becomes fairly low after the

weekend, favoring an average of non-CMC models and means as the

most palatable starting point for a deterministic forecast at that

time frame.



Rausch



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