Marine Weather and Tide Forecast for Kapalua, HI

DISCUSSION

Little overall change to expectations going forward today. The overnight period witnessed thunderstorms approach and pass northwest of Kauai while shower development further east, further away from the better instability and forcing, was underwhelming. The exception was along the land breeze boundary in the lee of Mount Haleakala where rates occasionally touched 1 inch per hour.
However, even in this case the more stable environment precluded greater shower depth and intensity mitigating flooding concerns.

Although no further strengthening of the low is anticipated, it will lose a couple more degrees of latitude today which will allow the eastern periphery of the mid-level cold pool to impinge on Kauai today into tomorrow leading to a relative maximum in instability during that time. However, the coldest air and greatest instability aloft will remain confined well northwest of the area.
Even so, ample moistening of low and mid levels has led to instability on the order of 1500 j/kg and equilibrium levels around 40kft over Kauai, more than sufficient for deep convection capable of producing torrential rainfall. Thus far, it is the lack of a low-level forcing mechanism that has prevented more widespread heavy rain from developing around Kauai. Nonetheless, orographic effects are evident on radar and outflows from upstream convection may prove sufficient to trigger additional downstream convective development. The Flood Watch therefore remains in effect through today.

Light to moderate low-level flow retains a SE component through the second half of the week which may allow showers to acquire a land/sea breeze character. This would favor a transition away from an organized heavy rain threat to one in which afternoon convective flare ups could produce pockets of heavy rain over island interiors from Thursday onward as the resident low peels off to the north and east. Long range guidance suggests moderate trades return for the first half of next week.

AVIATION

Moderate southerlies and increasing upper level support favor increased shower coverage over the western end of the state this morning. The gradual approach of low pressure positioned well NW of Kauai brings potential for a period of moderate to heavy rain today capable of producing widespread MVFR and localized IFR. VFR is forecast to prevail elsewhere, though isolated instances of heavy rainfall will still be capable of producing IFR on a localized basis. Thunderstorms are also possible over and in the vicinity of Kauai.

AIRMET Sierra for mountain obscuration remains in effect for Kauai.



MARINE

Gentle to moderate southerlies continues over the western end of the state with locally fresh SE prevailing over the eastern half.
A low settling several hundred miles northwest of the islands results in a chance of thunderstorms mainly in the vicinity of Kauai through Thursday.

The existing small, medium-period NW swell peaked yesterday afternoon and will subside through today with little in the way of surf for N and W facing shores expected thereafter. A slightly larger long- period NW swell is then expected this weekend, though surf is forecast to remain well below the advisory threshold for N and W facing shores.

A small, long period SSW swell will elevate surf along S facing shores above the summertime average, but still firmly below the advisory threshold as it peaks early this morning and holds through Wednesday. This swell then slowly declines during the rest of the week.

Lack of upstream trades favors near-to-below average surf along E facing shores, though some chop resulting from current SE winds may reach the waters off of E facing shores during the next several days.

HFO WATCHES/WARNINGS/ADVISORIES
Flood Watch through Wednesday afternoon for Niihau-Kauai-