Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
817 AM EDT Mon Oct 09 2017

Valid 00Z Tue Oct 10 2017 - 00Z Tue Oct 17 2017

A baroclinic low had become detached from the northern stream and
was parked well north of the Hawaiian Islands. The low will more
or less remain in place for several days while becoming stretched
and then eventually absorbed as part of another low pinching off
and retrograding out of the eastern Pacific. The low level pattern
will have relatively more bearing on precipitation potential over
Hawai'i, but in the near term this mid level low will leave a
trailing mid level trough axis across the islands along with
weakened trade winds for the next couple of days.

Soundings from 00z Monday revealed dry and stable mid levels. The
ingredients and opportunity for more widespread rain and heavier
rain will very gradually move back into place later in the week as
the easterlies reassert themselves at all levels, and a definable
850-700 mb trough passes through Wednesday and Thursday. The
initial surge of greater precipitable water will wrap around the
north side of the inverted trough...somewhat bypassing the Big
Island. By late Thursday and especially Friday, however, PW of
1.50 to 1.75 inches then settles down across the entire state, and
Friday looks like the day most favorable for heavy rainfall.

Over the next weekend strong high pressure builds over the
northeast Pacific, and low level winds over Hawai'i take on a
northerly, drying component, with the atmosphere drying out from
north to south. Overall the Pacific pattern is somewhat
challenging, including a period of strong and wavy northern stream
flow in the wake of a cyclone affecting the Aleutians mid-week.
This seems to have little influence on Hawai'i, hwoever, as models
are in strong agreement regarding the features at lower latitudes,
including the peak in heavy rain potential occurring Friday.

Burke