Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
254 AM EST Wed Jan 15 2025

Valid 00Z Thu Jan 16 2025 - 00Z Thu Jan 23 2025

Latest guidance continues to show the trades being disrupted by a
front that approaches and then passes through the main islands
during Thursday-Friday.  Instability/height falls aloft could
produce some areas of heavy rainfall as the front passes through
but the models have been consistent recently in keeping the
heaviest rainfall to the north.  Continuity is also good for the
next front that should reach the area during the weekend, with
trailing high pressure bringing moderate to brisk northeasterly
winds for Sunday and transitioning to moderate trades into early
next week. Guidance still expects precipitable water values to be
on the drier side of normal from the weekend into early next week
as upper ridging builds in, keeping most showers fairly light.

Guidance diverges noticeably by next Tuesday-Wednesday with
respect to the character of central Pacific upper troughing and
the resulting progression of the leading cold front.  There are
two primary clusters among the standard dynamical guidance, with
the ECMWF/CMC and their ensemble means slower and more amplified
with the trough versus the latest GFS runs and GEFS mean.  At the
surface this makes the difference between a slower/wetter frontal
passage on Wednesday in the ECMWF cluster versus a faster/drier
one in the GFS/GEFS along with trailing high pressure already
restoring trade flow by Wednesday.  00Z machine learning (ML)
models show typical spread, but on average recommend a compromise
solution (which is currently preferred) that would have the cold
front reaching at least into the eastern islands by 12Z Wednesday
with somewhat less heavy rainfall than forecast by the 00Z ECMWF,
while trailing winds would still be northeasterly versus the
trades of the GFS.

Rausch