textproduct: Honolulu

SYNOPSIS

Light winds, with afternoon sea breezes, will continue into the weekend. This will bring some clouds and showers to the interior of the islands each afternoon, with skies clearing at night. A cold front approaching the islands from the northwest will bring a line of showers quickly down the chain on Monday, and possibly linger near the Big Island Tuesday. A much drier airmass moves in right behind the front bringing a seasonable chill to the air late Monday into early Tuesday.

DISCUSSION

Some tweaks to the forecast this morning, but the general forecast philosophy continues. Light winds over the islands, particularly the smaller islands, will continue as we head into the weekend. This is due a ridge north of the islands sagging southward as a front passing north of the islands. The light winds will allow for afternoon sea breezes which will bring some clouds and showers to the islands during the afternoon and evening hours. Overnight land breezes will clear most of the clouds from the islands.

A much stronger cold front will approach the islands from the northwest Sunday, reaching Kauai late Sunday night/early Monday. There is good model agreement between the GFS and ECMWF with the timing of the front. The GFS is a little faster than the ECMWF, but both models shows a fast moving band of moisture moving down the island chain on Monday. There is some disagreement with regards to the amount of instability with the system. The National Blend of Models (NBM) thunderstorm probabilities are very low, and with the GFS and ECMWF not in any sort of agreement, and just a little higher. With the NBM probabilities low have continued to leave thunderstorms out of the forecast near the islands with the front.

Immediately behind the front, much colder dewpoints quickly spread down the island chain in a very stable airmass Monday night into Tuesday. The GFS is the coolest, with dewpoints dropping into the mid 50s, while the ECMWF in the upper 50s, and the NBM in the low 60s. With the tendency for the cooler dewpoints to follow such a front, the forecast reflects the GFS dewpoints. Northerly winds behind the front will quickly veer to typical northeast trades by Tuesday.

AVIATION

A ridge north of the islands will sink to the south, weakening the winds over the islands into the weekend. The light winds will lead to some clouds and showers forming over interior sections of the islands during the afternoon which could lead to brief MVFR conditions. Otherwise, expect VFR conditions to prevail.

No AIRMETs are in effect, and none are expected today.

MARINE

High pressure ridge will drift south over the central waters due to an advancing front to the northwest as light to gentle southeast to southerly winds will rule over the marine waters through Friday. The front will dissipate over the northwest offshore waters Friday as gentle east to southeast winds will prevail Saturday and early Sunday as the remnant front drifts northward, giving way to southerly winds again late Sunday. Due to the light winds, land and sea breezes are possible through the weekend. A stronger front will move down the island chain Monday and Tuesday, likely bringing fresh northerly winds in it wake.

Surf along north facing shores will remain small to moderate due to a gradually declining west-northwest swell through Friday. A storm low deepening south of the Aleutian Islands will generate a larger north-northwest (330 degrees) swell that will build rapidly on Saturday and peak through Sunday, producing surf near High Surf Warning (HSW) levels along north and some west facing shores. Another storm low is expected to develop closer to Hawaii this weekend and generate a larger long period northwest (320-330 deg) swell. This swell will likely produce surf above the HSW thresholds late Monday and Tuesday. Stay tuned as the low develops.

Surf along east facing shores will continue to decline through the weekend as winds over and upwind of Hawaii remain weak. Some increase in east shore surf is possible early next week. Along south shores, surf will remain very small through the forecast period.

HFO WATCHES/WARNINGS/ADVISORIES

None.