Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
350 AM EDT Thu Apr 02 2020

Valid 00Z Fri Apr 03 2020 - 00Z Fri Apr 10 2020

...Heavy rain potential next week...

A deep upper low to the northwest of the area near 40N will drop
southward to near 30N by late Friday. The 00Z guidance show this
upper low stalling for about 24 hrs before lifting slowly back
northward then eastward around 35N late Sun into Mon. The low will
weaken a bit as it moves past 160W late Tue then toward the
northeast thereafter. 00Z guidance was in good agreement overall
through about 5 days (00Z Tue) when the Canadian was
quicker/farther north than the ECMWF/GFS consensus (with the
ensembles). The attendant surface front to the east/southeast of
the upper low  (-4 sigma standardized height anomaly at 500mb)
will initially stall to the northwest of the area this weekend,
allowing deeper tropical moisture to lift across at least the
western half of the islands along a convergence zone. The models
have been wavering with how much moisture to stream northward and
where (western or central islands).  With precipitable water
values perhaps +2 to +3 sigma for a couple/few days, some locally
heavy rain will be possible. 00Z ECMWF was a rather extreme
example of that with near 10" of rain forecast for western Oahu.
By next Tue, the front is expected to start to push eastward, but
may only make it part way across the islands before slowing as the
surface flow weakens.


Fracasso