Waves, Winds, Weather compliments of 'Eddie Wen Go' at Hawaii Theater Friday
Your exclusive SNN Obs for this Wednesday Sept 17th 630am Update
Clear, light NE Trades giving way to 11am lite convective onshore seabreezes with more cloud build up into the afternoon. This pattern is set into Sunday. Low tide 4am. 1.8' High tide at Noon dropping out to a 0.4' Low tide at 730pm.
High Surf advsry dropped for southern exposures. The epic swell has eased another notch but still here. Buoys are 3' 14 seconds.
; all over, plus generals and still some powerful shorepound. East: Makapu'u: Holding the small below normal NE and S wrap 0-1 barely 2' set near the shore on the Keiki's side and semi smooth lite onshores. Great diving all windward. Diamond Head: Down and dropping on the SSW at 2-3 occ 4' with superb glass to offshores but likely onshores 11am ish then to the evening glass off. (see SNN Cam). Sandy's: Down and dropping on the South at a nice clean 2-3 occ 4'
Sponsored by Hawaiian South Shore.
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 17, 2014 3:54 AM HST
Synopsis Weak surface high pressure north of the islands will maintain gentle trade winds across the state today, with localized afternoon sea breezes developing. The ridge will break down from Thursday into the weekend, allowing for widespread sea breezes along with afternoon clouds and showers. Dry and stable air aloft will keep most rainfall amounts light. A tropical wave passing south of the area may bring an increase in rainfall, especially across the Big Island, with gentle trade winds resuming across the state by the later half of the weekend and into early next week.
Discussion Shower activity was most concentrated across Oahu during the night, with most windward and a number of interior sites receiving measurable rainfall. The other islands have remained almost entirely dry. Currently, showers are most prevalent over the leeward coastal waters well west of Oahu, and the waters southeast of the Big Island. Surface analysis depicts low pressure centered far northeast of the state, with a dissipating front/trough trailing SW to east and south of the Big Island. A 1022 mb high is centered about 1000 miles northwest of Kauai and is building slowly eastward, providing gentle trade wind flow across the state. Aloft, a weak upper level low is centered near Kauai, with a large mid/upper level ridge sprawling northwest of our region from west of the dateline to near 160°W. Mimic-tpw satellite imagery shows a stripe of higher moisture along the dissipating surface trough extending across the southern tip of the Big Island and south of the smaller islands, with another area of higher moisture approaching the state from the north. The 12Z soundings depict a rather typical profile, with inversions based around 7000 feet, and near normal pwats between 1.3 and 1.5 inches.
Surface high pressure will build slowly eastward to the north of the state today and tonight, maintaining a gentle background trade wind flow. Trades will remain light enough to allow localized sea breezes to develop once again this afternoon. Expect a hybrid pattern similar to that observed on Tuesday, with showers and clouds focusing on windward slopes during the early morning and nighttime hours, and across some of the leeward and interior areas during the afternoon. The area of increased moisture moving SW across the western and central parts of the state today and tonight will probably allow for a bit more leeward shower activity this afternoon, and windward shower activity tonight, than has been observed during the past 24 hours. A drier airmass appears likely to persist across the Big Island, and would expect showers to be less prevalent there.
From Thursday into the weekend, another cold front is forecast to drop southward across the north central Pacific. This will push the subtropical ridge south and east, disrupting the pressure gradient across the state. Local trade wind flow should weaken further or disappear entirely during this time, allowing for a period of more widespread daytime sea breezes and nighttime land breezes. This pattern will bring mostly clear nights and mornings with spotty showers over interior areas during the afternoons and evenings. The light winds will allow volcanic haze to build up around the Big Island, but it does not appear as if there will be enough southerly component in the flow to carry the haze over the smaller islands.
Forecast uncertainty increases during the weekend and into next week, when the models bring a tropical wave and associated surge of deep moisture northwestward toward the state. The 00Z guidance has generally trended a bit south with the wave, with the deeper moisture affecting mainly just the Big Island or possibly remaining south of the state altogether Sunday into Monday. It also appears that the increased pressure gradient between lower pressure to the south, and a narrow high pressure ridge between the islands and a stalled frontal boundary to our north should induce some increase in easterly flow over the state during this time. Have nudged pops down a bit for the smaller islands, keeping the highest pops over the Big Island.
Uncertainty increases further for next Tuesday and beyond, when the GFS drops another cold front southward into the central Pacific, weakening and veering our local wind flow toward the southeast. The ECMWF has a completely different solution for this time period with a building high pressure ridge in the central Pacific, causing increasing trades over the state. Will have to await future model runs which will hopefully resolve these differences.
Marine Overnight observations from the Barbers Point buoy show the south swell continuing to slowly decline, with peak energy values gradually shifting into the shorter wave period bands. This swell will slowly fade away through Friday. Surf along south facing shores will remain somewhat elevated through today as another small south swell arrives, but is expected to remain below advisory levels. Otherwise, a small northwest swell arrived late yesterday, as indicated by Waimea bay buoy data. Another small northwest swell will arrive later today, but surf along north facing shores will remain well below advisory levels.
An 0806Z ascat pass found gentle to locally moderate trade winds across the Hawaiian coastal waters, with a small area of winds greater than 15 knots in the Alenuihaha channel. These will probably be the strongest winds seen in our waters through the next several days, with wind speeds expected to begin decreasing later today. Winds and seas are expected to remain below small craft advisory levels through at least early next week.
BIG SURF PICTURE
The Jet down under has gone into ‘shutdown’ mode after a large trough last week generated what we’ve been claiming since 2 Friday’s ago…the year’s biggest SSW to south swell. Summer can’t last forever. After this long lasting event we’ll have to hope and pray.
Recent: We’ve been on the down trend to 2’ after a super long run of fun South swells that reached peak hts of 5’ at select reefs but mostly sets averaged 3’ from early Sept to Tuesday the 9th. Last weekend into early last week had a pair of swells from a pair of storms down under. We haven’t counted but since Aug to now there have been at least 8 sources of swell. The last of which will top it all off. Read below.
Next: Last Sunday a powerful Low tracked ENE under NZL with near hurricane force 65kt winds and seas near 50- 60’! The storm broadened further off the coast as the highest winds and seas weakened. But not before setting up a 1200 miles fetch. When storm have such extreme winds they generate long periods as we’ve seen since Friday: long fat 25 seconds leveling off to 22 sec Saturday and 20 sec Sunday. The swell hts will go from 1’ to 4’ and even 12 hours of 5’ 20 seconds. There will be moments at select reefs of warning level hts of 15’ crest to trough or 8’ local. The North shore can get 10’ from such values as the long periods have extreme refraction and shoaling off the bottom. Note: 20 sec period swell can be felt 1000’ down! This shows us how vital periods are to wave measurement.
Last: No sources of swell over 2’ out through next weekend meaning 2 weeks from now. There are marginal fetches in the Taz Monday 15th and another tiny Low off NZL Friday the 19th. Neither source may get here.
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.
The weak Jet is long and up around 40-50 degrees latitude. There’s some troughs and dips and by next weekend the Jet has a bit more speed and energy going from Japan to the Gulf. We are still in a state of transition.
Currently: the surf is barely 2’ remnants from our 1st real swell of the season that hit near 8’ Tuesday.
Recent: this nice WNW filled late Monday to 6’ and ramped Tuesday from a more NW angle. Source: Storminess Friday the 5th just east of the 180 dateline 1200 miles NW of us. By Saturday she had 30’ seas on the dateline and spun in place (occluded) as she broadened and weakened into Sunday…The result was swell of 5’ 14 seconds.
Next: Former tropical storm Fengshen will bump us up Sunday from the 15 sec WNW at 2-3’ midday and veer NW peaking at 4’ Monday into Tuesday with shorter 12 seconds. The system formed off Taiwan last Sunday the 7th and moved NNE as it broadened and weakend off Japan becoming a cold core Low off the tropics warm core. It then tracked East reaching the dateline Thursday the 11th as it merged and faded with a broad area of Low pressure centered in the Eastern Aleutians.
Last: A tiny weak low tracks east from the dateline this Wednesday and will only pull off some 2’ NW surf Tuesday the 23rd.
Recently and until Friday we’ve see tiny 1’ surf from the light local trades and seabreeze patterns; rare to see it this small this long. Then it’ll kick up from some T Storm action below.
Tropics: T Storm Odile has come into view today Sat. with a NW track and clipping Cabo etc Monday-Tuesday. By Thursday it’s nearly gone but still may shoot out some longer period 3’ East swell around Friday-Saturday the 19-20th.
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|