Better established light to breezy trade winds will hold well into next week. While trades are slowly making a come back, overall large scale winds will be weak enough the next couple of days to allow localized sea and land breezes to remain the alpha flow through Sunday morning. This pattern will favor thicker cloud build up with more frequent daily shower activity primarily focused over upslope windward mauka interior areas, partially clearing in the evening per drainage breezes over leeward spots. A westward passing band of more moisture-rich air, along with weak instability brought on by the approach of a vicinity eastern trough or weak area of lower layer convergence, will increase windward rain probabilities through Saturday evening. Broad surface ridging developing north of the state will maintain trades through next week.
A slug of higher moisture approaching from the east will be moving across the island chain through the day. Trades are returning and a benign east southeast flow pattern has become evident overnight on radar, especially on Oahu. Convergence over the Koolaus has generated a fair amount of persistent light to moderate rain with many sites along the windward slopes of Oahu picking up a half to around an inch of rain since late last night. A weak circulation, possibly in association with the tail end of a weak lower level trough approximately 100 miles offshore of Hilo, is slowly retrograding west. This will decrease regional stability enough to introduce areas of maritime showers that will periodically come onshore over windward exposures through Saturday. Rainfall behavior that was experienced last night along the spine and windward slopes of Oahu's higher terrain will be repeated across other islands through tomorrow as this relatively more moist air mass advances west northwest up the island chain through Saturday and produces frequent showers. Higher rain accumulations will focus across more eastern-facing, or windward, areas. Cloud cover will gradually thicken up through the day, especially mid to high clouds originating from ITCZ thunderstorm cirrus blow off getting caught up within upper level southwesterlies /subtropical jet traveling over the state. While trades will make the 'feel' of humidity more tolerable, more overcast afternoon skies will keep many windward (coastal) communities in the mid to upper 70s while mostly sunny leeward lighter wind/rain/cloud shadowed locations will warm into the lower to middle 80s.
Upper level support, or more efficient streamline diffulence, will be in play, introduced by the subtropical jet passing over the islands. This strengthens the 'more wet than dry' argument in closing out the first full week of May. Surface troughing northeast of the islands will be retrograding back into the central waters through Saturday. This feature, albeit very week, will likely be the impetus to the regeneration of maritime showers caught up within the trades that will periodically come ashore the next few days. Higher rain chances will reside over the windward sides of islands but leeward areas will also get into the action from either sea breeze convergence or better organized cells maintaining their structure enough to wet leeward slopes along their west southwest journey. A few areas of drier air will advect in from the east early next week and this help lower widespread rain episodes Sunday through Tuesday. A more shallow mid week boundary layer will kick off a few days of more robust trades focused on Monday-Tuesday through Thursday. Upper ridging expands in from the northwest by Tuesday with weak troughing forming west of the state later in the week. This translates to a more typical seasonal early to mid week trade wind and precipitation behavior. The timing of when you will receive a quick dose of rain will strictly be dependent upon when these eastern bands of higher mid to lower level moisture stream across the island chain.
Light to moderate trades will return across the region, lasting through much of next week, yet will be weak enough the next couple of days to retain localized land-sea breeze development through the weekend. Expect clouds and shower activity to form, not only over windward areas, but over leeward and interior areas during the afternoon hours. This will result in occasional MVFR conditions. Otherwise, VFR conditions will prevail.
No AIRMETs in are effect at this time.
A weak trough east northeast of the islands will keep trade winds light to locally moderate across all local waters today. By this weekend, however, a surface ridge building northwest of the state will bring a return of moderate to locally fresh trades. A Small Craft Advisory may be needed for the typical windy waters surrounding Maui and the Big Island by early next week as the high expands eastward and trade winds strengthen further.
A declining moderate, medium-period, northwest swell will bring elevated surf to north and west facing shores today. Surf will continue to decline through the weekend as the swell fades.
A small, long-period south swell should provide a small bump in south shore surf through the weekend. Another small, long-period south swell is possible mid-next week.
Surf along east-facing shores will remain slightly below normal today, due to the lack of strong trades over and upstream of the islands. East shore surf will gradually increase this weekend into early next week as trades make a slow return.
None.
