Waves, Winds, Weather compliments of Big City Diner
Your exclusive SNN Obs for this Tuesday Sept 30th 640am Update
Unstable atmosphere but for now: Clear leeward with super light Trades leading to seabreezes and cloud build up 11a-5pm. High tide 9a 1.9'. Low tide 430p 0.5'.
Chance of 5' bombers Thursday. East: Makapu'u: Down and holding the new East swell and dying NNE 1-2' with longer lulls as it weakens slowly, breaking mostly inside and its decent slight bumpiness and some clouds and fun. Diamond Head: Up and rising on the new 1ong period SSW and holding the tiny SSW/SSE at 2-3' and 4' toward Black Point on sets on the take off & it's nice and smooth with some morning sickness/wooble with light side-offshores. (see SNN Cam). Sandy's: Up and rising on the new SSW mixing with the old SSW with clean 2-4' sets at Generals, smaller at Full and half Pt and into the big close out shorebreak.
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THE WHERE, WHEN & WHY OF HAWAII’S WAVES & WEATHER: A VIDEO PRESENTATION BY SNN
Winds Statewide in a glance ...go HERE (this link is also the 4th drop down under weather)
Sep 24, 2014 4:51 AM HST
Winds have increased to advisory criteria at multiple sensors on Mauna Kea during the past hour. A wind advisory has been issued for the Big Island summits through 6 pm today. No other changes, previous discussion follows.
A moderate to locally fresh trade wind flow will focus shower activity over windward slopes today, although showers will reach some leeward areas as well, especially on Kauai. Showers will increase tonight through the end of the work week, as an area of enhanced moisture along a weak shear line moves over the island chain from the north. The wet trade flow will persist over portions of the state through the weekend.
scattered showers have developed across parts of the Hawaiian coastal waters during the night, although measurable rainfall at the gauges has thus far remained confined to Kauai. A 1024 mb surface high centered about 900 miles northwest of Kauai continues to drive moderate to locally fresh trade winds across the state. Satellite imagery reveals a diffuse shear line approaching the state from the north, extending far southwest and west from an intense low pressure center in the distant northeast Pacific. Aloft, a deep layered anticyclone is centered near the position of the surface high to our northwest, with dry and stable conditions prevailing aloft over the region. The 12Z soundings show that a well defined inversion is lacking, but stable conditions prevail in the mid levels, with pwats ranging from a below normal 1.21 inches at Hilo to an above normal 1.65 inches at Lihue. Mimic-tpw satellite imagery shows the leading edge of a wide east-west oriented band of higher moisture extending eastward from Kauai to about 80 miles north of Hilo. This moisture band is shifting to the southwest, and will spread across much of the state later today.
A wetter trade wind pattern is forecast to develop across the state during the next 24 hours. Continued moderate to locally fresh low level trade flow will generate increasing shower activity across windward and mauka areas, as the axis of enhanced moisture along the old shear line sinks southward and eventually stalls across the central part of the state. Showers should remain focused primarily across windward areas today, but expect a significant increase in rain chances across the smaller islands tonight through at least Thursday night. Windward areas will see a rather wet pattern during this time, with above normal rain chances across leeward areas as well. A more typical pattern seems likely on the Big Island, with scattered showers windward, and widely scattered afternoon seabreeze-driven showers on the Kona coast. Relatively stable conditions aloft along with quick motion of the showers in the continued trade wind flow should keep most rainfall amounts light to moderate. Uncertainty increases late Thursday night through Friday night, when the GFS shifts the enhanced moisture axis temporarily back to the north of the state, while the ECMWF keeps the moisture axis overhead. Have leaned toward the wetter GFS solution for now.
Uncertainty increases further during the weekend and into early next week, when many of the models continue to call for a mid to upper level trough to move near or over the island chain from the southeast. This increasing instability aloft could act on the stalled axis of enhanced moisture over the state to trigger periods of localized heavy rain, along with the potential for isolated thunderstorms. Trades may weaken somewhat during this time as well, allowing for slower shower motions and potentially a transition into a more widespread convective/seabreeze pattern. The 00Z ECMWF and GFS appear to have come into somewhat better agreement during this time period, but at this point confidence remains too low to fully buy into this potentially active weather scenario, and we continue to leave mention of heavy showers or thunder out of the official forecast at this time. The forecast for the weekend and early next week may require significant refinements as we move through the next few days.
The overnight ascat pass found areas of 25 knot winds in the Alenuihaha channel and south of the Big Island. The 12Z Lihue sounding also continues to show low level winds of greater than 20 knots, and the high resolution WRF models maintain advisory levels winds in the typically windy waters around Maui county and the Big Island through today and tonight. Have extended the existing small craft advisory through 6 am Thursday morning. The wind forecast for Thursday through Saturday remains uncertain, with models depicting a belt of enhanced trade winds dropping southward across the coastal waters along an old shear line. Some of the guidance indicates advisory level winds during parts of this time period as well, and the SCA may need to be extended further.
No major swells are in store through the weekend. A series of small, about 2 to 3 feet, swells from the NNW to NNE will pass through late this week and through the weekend. A small SSW swell will arrive Saturday, with a potentially more significant long period southerly swell forecast to arrive early next week. Otherwise, short period trade wind driven seas are expected to build a bit through the next couple of days, with surf along east facing shores remaining well below advisory levels.
Small craft advisory until 6 am HST Thursday for Maalaea Bay, Pailolo channel, Alenuihaha channel, Big Island leeward waters, Big Island southeast waters.
BIG SURF PICTURE
The Jet down under is still looking good for storm enhancement and steering toward the Islands. There’s a thick North branch and a decent southern branch flowing NE from off NZL the next few days. However, the high pressure are trying to squeeze out the troughs and block off NZL around Monday the 29th. Still, we get the N bound flow under Tahiti at this time allowing for more energy to come our way. Looking good.
Recent: We’ve been on the down trend to 1-2’ background SSE for awhile but that’s all going to change again for a super long round of back to back to back SW-South swell.
Next: A small bump from a Taz Sea fetch last Friday should pop 1’ 14 seconds on Barbers Buoy late Friday and rise into Saturday with long lulls of 1-3’ surf into Sunday. This will be overrun by the next source.
Next: The above Taz storm drifted east over NZL and gets out of to the NE side by Monday with a 40-45kt fetch nosing to about 3000 miles to our SSW or 1000 miles closer than the usual region of swell generation. Reinforcing SSW could hit 2-4’ Tuesday-Wednesday.
Next: Far below the above fetch is a much bigger stronger Low to the SE of NZL tracking ENE M-W and will add to the existing seas of the first Low to the NE. The apparent fetch from these two mergers gets nearly 1000 miles long creating yet another long lasting episode of fun in the sun and surf. Forerunners could pop 22 seconds Sunday night the 28th but it will be a slow rise over Monday-Tuesday. Still top reefs could see some 5’ sets Tuesday night and peak near 3-6’ on Wednesday-Thursday. We will have 2-3 days of high surf advsrys.
Next: Within the large Jet stream trough is yet another Big Low with its reinforcing broad 40-45kt fetch building 30’ seas Wed the 24th. Plus, the track is NE garnering a captured fetch (fetch points the same way as the storms center track) which helps grow the seas to their full potential. Thursday the track veers East under Tahiti so this swell will start out SSW and veer S. There’s a ton of storm activity far below French Polynesia so Tahiti’s going to score.
Next: Saturday the 27th shows a smaller compact Low tracking NE from below NZL which will bring up some 2-3’ SSW Saturday the 4th.
Last: Too early to claim but WW3 hints a whopper under Tazmania Oct 2nd…
Note: High Surf threshold for South swell is 8’ crest to trough and 15’ for NW swells. Why the large threshold difference is likely an extra safety precaution where populations are greatest.
Wednesday the Jet Stream is split 1200 miles off Japan with a larger trough looping up and down under the east Aleutians which leads to the first big NW hitting the NW coast. The fall regime change in the Jet is conducive to 3 rounds of fun NW swell. The split moves our side of the dateline by Saturday the 27th then consolidates and fattens up Sunday-Tuesday with a large dip SE near the dateline just 1200 nearing to 900 away. This will likely mean lighter winds and iffy weather early Oct. But it also spells WAVES.
Recent: It’s been tiny 2’ or less with minor pulses here and there from the NNW however, that changed today.
Currently: the surf has bumped up to 3’ Wednesday afternoon from the NW. We had a powerful Low off Kamchatka last Friday and it stayed over 2000 miles away limiting the size to max 3’. There’s also a N mixing from a nearby Low 1200 miles to our N. This is the same storm that intensifies as it tracked E toward the west coast so we’ll get N to NNE into Saturday. They’ll be 8 and even 10’ for N Cali and Oregon etc.
Next: Thursday-Friday the NPAC looks quite with only a tropical storm far off Taiwan building and tracking N to Japan. Hold on to this one.
Next: Upgrade for Saturday's storm: a Low spawns of the Kuril Islands with up to 30’ seas and a nice ESE track with a partially captured fetch; it reaches the dateline Sunday the 28th. Look for 5’ 16 seconds buoys oct. 1st refracting/shoaling swell for some 5-7' NW surf at Sunset Wed afternoon into Thursday morning. Could see some high surf advsry sets.
LAst: On Tuesday the 30th the tropical system above becomes a gender bender (warm to cold core Low) and feeds into the Jet energy near the West Aleutians intensifying Wed-Thursday as it moves N into the Bering sea. Still, tho’ distant its forecast to be powerful enough for 16 second forerunners and some more 4-6’ NW surf filling Sunday Oct 5th into Monday. Iffy confidence.
Windward side: With the return of the trades we’ve had a boost to 1-2’ ENE and we’ll also get some small N wrap from the above NPAC source. The surf should range from 2’ to maybe 3’ due also to a shear line moving South across the Island into Thursday. This is an abrupt change in wind speed and/or direction.
Tropics: A powerful system is on the charts Tues-Thu far off the Philippines moving NE. Too early for specifics but it's likely to be a typhoon. Things have calmed down off Baja.
FETCH: Often called the fetch length, is a term for the length of water or distance over which a given wind direction has blown. Fetch length along with the wind speed (or strength) determines the size of waves produced. The longer the fetch length and the faster the wind speed, the larger and stronger the wave will be and vice versa.
CAPTURED or FOLLOWING FETCH: Not only does the fetch length determine the power and energy of the wave. Additionally, if the winds/fetch are blowing in the same direction as during the wave's or storm's lifetime, the wave will in turn be even stronger. The fetch is related to the orbit of the wave and track of the storm.The longer the wind drags along the sea the more energy the wave will have. This can be seen not just in vertical height measurement but in wave period (the measurement of waves through time).
WAVES PERIOD:Time, in seconds, between the passage of consecutive wave crests past a fixed point. In general the longer the period the bigger the wave. Windswell or 'close interval' swells are under 10 seconds. Big 'ground swells' are 17-20+ seconds (note: a 20+ second swell needs storm force 50+kt winds blowing over a 1500 mile fetch to be fully developed' into 20-25' beasts; these 20 second waves can be felt 1000 feet down!). This is why they jack so much more, pulling large amounts of H2O off the outer reefs.
More generic marine definitions click this link http://www.prh.noaa.gov/hnl/pages/marinedef.php
....All surf height observations and forecasts are for the full face surf height, from the trough to the crest of the wave.
|North-Facing Shores||15 Feet (8')||25 Feet|
|West-Facing Shores - Big Island||8 Feet (4'+)||12 Feet|
|West-Facing Shores - Remaining Islands||12 Feet (7')||20 Feet|
|South-Facing Shores||8 Feet (4'+)||15 Feet|
|East-Facing Shores||8 Feet (4'+)||15 Feet|