SynopsisA front will provide a wet trade wind pattern for some of the islands through the new work week as a front moves slowly down the island chain. The front, now near Oahu, will stall and dissipate over the Big Island the second half of this week. The trade winds will strengthen today through Tuesday to moderate speeds. Then we will loose the trades once again this coming weekend.
DiscussionAs of 330 am HST, the front is in the Kauai Channel. It is having a difficult time advancing on to Oahu, likely due to an offshore land breeze coming off the north shore. The front should continue eastward across Oahu later this morning and to Molokai this afternoon. The front continues on to the rest of Maui County tonight and Tuesday. The models keep the front together while moving through Maui Tuesday night and on to the Big Island Wednesday. The GFS has the front stalling over the Big Island through at least Friday while the ECMWF model has the front moving south of the Big Island on Friday. These models could be keeping the front as a feature too long. The front will disperse once the trades turns east to west which is about Friday.
As noted in the previous discussion, the slow moving nature of this front and with its persistent and almost continuous trade showers may lead to some flooding issue and mud slides on the windward side of the larger islands from especially Molokai to the Big Island this week. The moisture is shallow with cloud tops no higher than 12k feet but this moisture will be plentiful acting on an orographic barrier. So we will be monitoring the situation closely this week.
As for the trades winds...the forecast calls for gradually strengthening to mainly moderate speeds tonight and Tuesday. This is a result of a 1025 mb surface high moving to a position about 720 miles north of Kauai tonight. The trade wind starts weakening after Thursday as the high starts to break down. The islands will then transition to a convective daytime sea breeze mode about Friday and persist through the weekend. The high north of the islands will be replaced by a trough.
AviationVFR will prevail over most areas through Memorial Day. However, a weak front that has been moving over Kauai and is approaching Oahu may generate TEMPO MVFR conditions in northern and windward sections of these isles as it continues to head east and southeast. More daytime convective clouds and showers will likely develop over Maui County and the Big Island by the late morning and afternoon hours today as the front approaches. MVFR will mainly affect interior and mauka locales on those islands.
No AIRMETs are currently in effect.
MarineAs a weak front presses slowly across Oahu and Maui County during the next 24 hours, a modestly strong trade wind regime will build over the surrounding waters of these islands. The winds are forecast to remain below small craft advisory level. However, some sections of the coastal waters may come close to small craft advisory level criteria. We will be monitoring closely for these conditions. We will loose the trades again late this week as the source of the trades, a high pressure system 720 miles north of kauai, dissipates and is replaced by a trough.
A small northwest swell should gradually increase over the islands this morning, peaking later today, before subsiding into Tuesday. The Waimea is currently reading 2 ft 13 seconds. The south swell is also holding well as noted by the Lanai buoy with a reading of 2.3 feet at 15 secs.
Another small southwest swell is expected to bump surf up slightly again for south shores Wednesday. The return of strengthening trade winds will gradually re-introduce short period choppy surf to east facing shores during the coming week.