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

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

Today's models and ensembles continue to agree reasonably well for
most aspects of the forecast.  The trade pattern with light to
moderate windward-focused showers will transition to strengthening
southeasterly to southerly flow over the state as a front
approaches from the west.  Guidance still shows a considerable
amount of tropical moisture (PWATs reaching up to 3+ standard
deviations above normal) along this front with heaviest rainfall
likely affecting western areas on Tuesday and central locations on
Wednesday.  Some heavy rain may extend into the Big Island by
Thursday as the front reaches the eastern half of the islands,
though with totals that may be a little lower than over areas
farther west.  The front should weaken toward the end of the week
with the lingering moisture band returning back to the northwest
from Friday into the weekend as easterly to southeasterly trades
likely develop.  An intermediate solution for frontal position
looks reasonable, given that the spread is well within typical
error ranges for the time frames of interest.  By next weekend
another upper trough with a possible embedded low may approach
from the northwest, with a leading front coming into the picture
west of the islands.  The 18Z/00Z GFS and to some degree the GEFS
mean are on the more extreme side of the envelope with the
southeastward amplitude of the upper trough, leading to a front
that could reach far enough east to refocus rainfall over the
islands.  Remaining guidance suggests that the front should stay
farther west to varying degrees so would recommend at least a
compromise in that direction.

Rausch