Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
333 AM EDT Sun Jul 16 2023

Valid 00Z Mon Jul 17 2023 - 00Z Mon Jul 24 2023

The core of the main mid-latitude high is expected to be centered
well to the northwest of Hawaii through most of the forecast
period, generally near 45N/170W, with an southeastward extension
centered between 35-40N for most of the forecast period.  This
should still provide enough pressure gradient to sustain mainly
east-northeast trades of 10-20 mph through the early part of the
week, with showers mainly for the windward terrain.  There is good
agreement among the ensemble means for this scenario.

Looking ahead to the middle of the week, what is now Hurricane
Calvin is forecast to track in the general direction of the Big
Island as a weak tropical storm based on the latest forecasts from
the National Hurricane Center, with the most likely time of
arrival early Wednesday morning.  This would result in a round of
very heavy rainfall for the Big Island and Maui through late
Wednesday evening, along with high surf and gusty winds.  The
potential for 4-8+ inches of rainfall is appearing increasingly
likely for parts of the Big Island with this event, and this would
increase the threat of flash flooding.  As the system continues to
weaken, lighter impacts are likely for the central and western
Islands, and then a return to normal trade winds and rainfall
patterns going into the end of the week and beyond.

Hamrick