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CJSB
Legend (inyourownmind)
Reged: 04/08/09
Posts: 427
Loc: Santa Barbara
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Re: El Niņo
12/02/09 04:15 PM
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12/01 Update via SS:
MJO/ENSO Update (reference): As of Tuesday (12/1) the Madden Julian Oscillation (MJO) was in the Active Phase supporting the continued evolution of El Nino. The ENSO (El Nino Southern Oscillation) index continued in the negative range with the Daily SOI index up some to -8.10 (almost 20 consecutive days in a row). The 30 day average was up to -6.15 while the 90 average was down some to -6.12. This continues looking more like a legitimate El Nino based solely on the SOI.
Wind anomalies at the 850 mb level (approx 5000 ft up) as defined by models continued indicating a strong and broad area of westerly anomalies consistent with the Active Phase covering the the Eastern Indian Ocean and West Pacific reaching just over the dateline and pushing east from there. The Active Phase is to continue pushing east reaching into the Eastern Pacific on 12/5 and tracking east from there while slowly fading, reaching Central America on 12/10 but still holding ground on the dateline, then slowly dissipating through 12/20. A weak version of the Inactive Phase is forecast trying to get legs in the Indian Ocean at the same time, reaching New Guinea on 12/20 and nearly dissipated. This Active Phase episode is expected to increase storm activity in the North Pacific through mid-December.
Sea Surface Temp anomaly data (11/30) indicates that warmer than normal waters are consolidated on the equator from Ecuador west to the dateline and even west of there, but have been steadily pulling away from the Baja coast. The lack of a real Kelvin Wave in a while is likely not helping that situation. But with the coming of a new strong Kelvin Wave (see below) there is some anticipation that warmer waters might build to the north. From an El Nino perspective, it make no real difference though. The expanse of the warmer waters continues to hold on equator, covering slightly more area and filling in with the warmest waters covering greater area now. Overall the warm water signature remains non-exceptional, but clearly in the moderate El Nino category and building very slowly but steadily.
Of interest, the water temp anomaly data provided by NOAA/NESDIS (satellite based) versus the TAO/TRITON buoy array, present different depictations of the same event. The TAO array suggests max heating is occurring on the dateline, with temps easing as one tracks east, while the satellite based data from NOAA presents an analysis of continuous warm waters over the length of the equator from Ecuador to the dateline. The difference is in how the data is collected (buoys at fixed points versus a satellite view of the entire playing field). We're siding with the satellite view not because it is more favorable, but because we believe it more accurately represents reality. The buoy arrays strength is in waters temps at depth (i.e. for detecting Kelvin Waves). This is exactly what the array was built to detect. The satellite view cannot do that. Likewise, the satellite has far superior coverage.
Below the surface on the equator things continue to look favorable. A steady flow of warmer than normal subsurface water continues tracking from the West Pacific (150 m below the surface) under the dateline and breaking the surface near Central America as it has for months now. As of 12/1 a core of 5 deg warmer than normal sub-surface water is currently tracking east located at 110W with it's leading edge starting to move off the charts, and into the Central American coast. This should fuel an increase in the warm water surface pool as it erupts along the coast building there and eventually tracking back west on the equator driven by trades. This Kelvin Wave that first appeared under the dateline on 9/17 and tracked steadily east through 12/1. and was the result of a prolonged persistent westerly surface wind flow that had been in-place west of the dateline from 9/8 and continued into 11/5.
Over the Equatorial Pacific and consistent with the Active Phase, surface winds started to move anomalously from the west extending the whole way from Indonesia to a point south of Hawaii, with weak real west winds confirmed in the far West Pacific. A new Westerly Wind Burst started to develop on 11/28 and was very obvious on 11/30 with fully blowing west winds near 165E, and strong. Suspect another tropical system is building there. This could help to form yet another Kelvin Wave which would be good. The Kelvin Wave currently tracking east was formed from a prolonged bout and multiple pulses of westerly winds and westerly anomalies that occurred from 9/8 through 11/2. At one point towards it's end the anomalies reached the whole way from the West Pacific to almost Ecuador. Embedded in that run were Typhoons Dujuan, Choi-Wan, Parma, Melor and Nepartak. All this helped to deepen the surface warm pool in the tropical Eastern Pacific.
El Nino is expected to affect the global atmospheric weather pattern at least through Spring of next year if not into the middle of summer. All data suggests this will not be a strong El Nino, more likely a moderate one. NOAA's last update (11/5) forecasts the same outcome, though hints at some uncertainty. In short, all the best models aren't exactly sure how this is going to play out. Regardless a solid accumulation of warm water in the equatorial East Pacific is evidence in-favor of continued development. As long as there continues to be WWB's (as there obviously is), then warm water will be migrating east, and the warm water pattern will hold if not build, and the atmosphere above it will respond in-kind to the change (towards El Nino). At this point there is no evidence to suggest this El Nino will stall or dissipate. The only remaining question is whether it will hold, or grow. And current data indicates that the warm pool will hold if not slowly build. And historically it is already larger and strong than any other in the past 12 years.
The current El Nino is gaining strength, with a 2 degree water temp anomaly in the tropical East Pacific the likely outcome. Coverage is pretty solid for this event, but the lack of really high water temp anomalies will likely limit it's strength. Strong El Ninos bring lot's of bad weather to the US West Coast, along with the potential for storm and swell enhancement. A moderate El Nino provides storm and swell enhancement, a gentle but steady push/momentum in-favor of storm development rather than the manic frenzy of a strong El Nino, but without all the weather associated with a strong event. So in many ways a moderate El Nino is more favorable from a surf perspective. As of right now things remain better than anything the Pacific has seen in the past 12 years regarding anomalous sea surface temperatures, besting anything since the big El Nino of 1997. That is very good news. But the lack of anomalous water temps exceeding 3 degrees and an unremarkable SOI suggests a modest El Nino at best. Still, it should be enough to provide storm enhancement, and a better than average winter surf season for the North Pacific, and still likely better than anything in the past 10 years. Better yet, if it's not too strong (as this event appears to be) perhaps it will not degrade into La Nina the year after (which typically happens after stronger El Ninos), but hold in some mild El Nino like state for several years in a row. This would be an even better outcome.
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