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FXHW01 KWNH 130759

PMDHI 



Hawaii Extended Forecast Discussion

NWS Weather Prediction Center College Park MD

359 AM EDT Mon May 13 2024



Valid 00Z Tue May 14 2024 - 00Z Tue May 21 2024



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

weekend...



Continue to expect a relative lull in organized heavy rainfall as

the compact upper low just north of the state steadily fills in

place early this week.  There will still be the potential for

localized enhanced rainfall within a regime featuring light to

moderate southeasterly background flow with some sea breeze

influence on showers.



From midweek onward the latest dynamical and machine learning

model guidance has been fairly consistent and agreeable over the

past day in depicting a multi-day wet and stormy pattern due to an

unseasonably deep/south upper low expected to settle

north-northwest of the state.  Consensus maintains the idea that

closest proximity of this upper low should be around

Wednesday-Thursday with a position just west of 30N 160W, followed

by only gradual weakening and north/northwest drift (00Z CMC being

the southeastern exception by next Monday).  Most of the current

guidance shares the general scenario of an associated cold

front/surface trough reaching into the central islands and

focusing heavy rainfall potential over that part of the state

mid-late week as leading southerly flow helps to increase

precipitable water (PWAT) values.  Then during the weekend the

surface boundary and heavy rainfall focus will likely drift back

into the western islands, as the supporting upper pattern shifts

northwestward a bit.  As this occurs, the GFS/ECMWF and their

ensemble means suggest that a further increase in PWATs may occur

with the ensemble means reaching up to 3-4.5 stdevs above

climatology and the operational GFS/ECMWF runs reaching even

higher.  Thus the heaviest rainfall during the event may be over

the western islands during the weekend.  Most guidance shows the

rainfall axis retreating to just west of the western islands by

next Monday.  Continue to monitor forecasts for any potential

adjustments in specific details.



Rausch



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