Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
325 AM EDT Tue Jul 18 2023

Valid 00Z Wed Jul 19 2023 - 00Z Wed Jul 26 2023

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

Tropical Storm Calvin is forecast to track in the general
direction of the Big Island as a weakening 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 with strong easterly upslope flow,
along with high surf and gusty winds.  The potential for 4-8+
inches of rainfall is expected 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 greatly improved weather conditions going into the end
of the week and beyond.

Hamrick