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FXHW01 KWNH 120800

PMDHI 



Hawaii Extended Forecast Discussion

NWS Weather Prediction Center College Park MD

359 AM EDT Sun May 12 2024



Valid 00Z Mon May 13 2024 - 00Z Mon May 20 2024



...Heavy rain threat mid-late week and possibly extending into the

weekend...



In the short term, latest guidance has changed some for the

details of the compact upper low hovering just north of the main

islands--having it weaken in place before shearing out versus

tracking more steadily eastward.  Still, weakening of the low

should offer a brief lull in organized heavy rainfall potential

early in the week.  The surface trough initially over the state

should drift westward, allowing for a period of light to moderate

southeasterly background flow.  This should lead to a mix of

windward and sea breeze focus for showers.



From midweek onward, latest guidance has improved its clustering

for the unseasonably deep/south upper low expected to settle

north-northwest of the state.  Dynamical guidance and

ECMWF-initialized machine learning models agree that closest

proximity of this upper low should be around Wednesday-Thursday

with a position just west of 30N 160W.  This represents a

gravitation toward what was the eastern side of yesterday's

envelope as represented by the 00Z/11 GFS run.  This clustering

now suggests that the associated surface front will help to focus

an axis of heavy rainfall over the central islands mid-late week

as deep moisture flows northward.  By Friday-Sunday the guidance

shows the upper low wobbling northwest to some degree while

ridging builds southeast of the state--leading to a gradual

westward shift in the heavy rainfall axis.  Differences in

specifics are well within typical spread/error for 5-7 days out in

time with no pronounced clustering, favoring an intermediate

solution where discrepancies arise.  Indicating the abundant

moisture that may be available for heavy rainfall, the 00Z

GEFS/12Z ECens means show precipitable water values reaching up to

3-4 stdevs above normal for a time late this week and/or the

weekend, while the 00Z GFS/ECMWF show some higher deviations for

portions of that period.  Continue to monitor forecasts for

further trends, as minor adjustments in specifics will be

important in resolving effects at any particular location.



Rausch



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