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Pacific ENSO Update

4th Quarter, 2012 Vol. 18 No. 4


CURRENT CONDITIONS

According to the U.S. Climate Prediction Center (CPC), the climate of the Pacific Ocean basin continues to straddle the borderline between ENSO-neutral and weak El Niño. For several months, the Pacific basin has been in an El Niño watch, but now has downgraded the ENSO Alert System Status to “Not Active”. La Niña conditions ended in early 2012, and the climate system then entered ENSO-neutral. It was thought that a transition to El Niño would occur sometime in the latter half of 2012, with El Niño most likely to become established during the Northern Hemisphere (NH) fall months. Whereas the equatorial Pacific Ocean began to show signs of El Niño with an observed warming of both the sea surface temperatures (SSTs) and the sub-surface waters down to 300 meters, the atmosphere showed few signs of an impending El Niño. The monsoon was weak or absent at low latitudes (e.g., throughout most of Micronesia) and tropical cyclone development occurred mostly to the west and north of the average longitude and latitude of development. Sea levels also remained higher than normal across Micronesia, which is not typical of El Niño.

Rainfall has been generally above normal across most of Micronesia from Palau in the west through Chuuk and Pohnpei in the east, and in Guam and the CNMI to the north (see Figure 1). In the far eastern portions of Micronesia (e.g., Kosrae, Kwajalein and Majuro), rainfall has been below normal. In late July and early August, a strong surge of the southwest monsoon spread eastward well to the north of Micronesia. Several tropical cyclones formed to the north and west of the region. During August and September, southwesterly winds again surged, but this time extended across Yap and Palau, and occasionally as far eastward as Guam, the CNMI and Chuuk, giving these islands abundant rainfall from passing tropical disturbances and mesoscale clusters of heavy showers and occasional thunderstorms.

Parts of Hawaii remain in extreme drought. Areas of Maui County and the Big Island head into this coming wet season under extreme drought. Reports from Maui include: Up country agriculture continues to be negatively and significantly impacted by drought; ranchers have had to increase irrigation, supplement feed for livestock and reduce herd sizes; axis deer, seeking food and water, have been encroaching on forage previously reserved for livestock.; and a 10% reduction request of water usage remains in effect for central and southern parts of the island. On the Big Island, worsening drought conditions have also forced some ranchers to reduce their herd size by 25% and supplement feed for their livestock. Flower growers have had to spend much money to fill catchment tanks for irrigation and the lack of rainfall has decreased the amount of nectar available for bees. This has negatively impacted the bee industry on island.

On Kauai, Molokai and Oahu, there are reports of poor pasture and general vegetation conditions. On Molokai there has also been an encroachment of Axis deer leading to crop damage and the water level in the Kualapuu Reservoir remains very low. This continues the mandatory 30% cutback in irrigation water consumption. On Lanai, especially in the middle and lower elevation areas, plants and animals have been struggling to survive.

Although the locations in Hawaii will soon enter their winter rainy season, dry conditions are expected to continue in the first few months of 2013.

The rainfall forecast is somewhat uncertain across Micronesia during the next three to six months. If El Niño were to become established late in the year, there is a possibility of some general dryness across the region in the late winter through spring. If ENSO-neutral conditions persist as is now the current expectation, then rainfall would likely be near normal with some isolated dry conditions noted, particularly in the northern RMI and perhaps in the CNMI. In the absence of a moderate or strong El Niño, it is unlikely that widespread severe dry conditions would occur. The local variability summaries that follow generally reflect the ENSO-neutral scenario.

The following comments from the EL NIÑO/SOUTHERN OSCILLATION (ENSO) DIAGNOSTIC DISCUSSION were posted on the U.S. Climate Prediction Center/NCEP and the International Research Institute (IRI) for Climate and Society web site the 8th of November, 2012:

“ENSO Alert System Status: Not Active

Synopsis: ENSO-neutral is favored through the Northern Hemisphere winter 2012-13.

During October 2012, the Pacific Ocean continued to reflect borderline ENSO-neutral/ weak El Niño conditions. Equatorial sea surface temperature (SST) anomalies increased across the Pacific Ocean during the latter half of the month, which was also reflected in the Niño indices. The oceanic heat content (average temperature in the upper 300m of the ocean) anomalies also increased slightly in association with the downwelling oceanic Kelvin wave. While the subsurface and surface Pacific Ocean has recently warmed, the tropical atmosphere remained largely consistent with ENSO-neutral. Upper-level and lower-level winds were near average, and the strength of anomalous convection decreased over the past month. Thus, the atmosphere and ocean continue to indicate borderline ENSO-neutral/ weak El Niño conditions.

Relative to last month, the SST model predictions more strongly favor ENSO-neutral, although remaining above-average in the Niño-3.4 region through the Northern Hemisphere winter 2012-13. While the tropical ocean and atmosphere may resemble a weak El Niño at times, it is now considered less likely that a fully coupled El Niño will develop. Therefore, the previous El Niño Watch has been discontinued as the chance of El Niño has decreased. While the development of El Niño, or even La Niña, cannot be ruled out during the next few months, ENSO-neutral is now favored through the Northern Hemisphere winter 2012-13 (see CPC/IRI consensus forecast).

This discussion is a consolidated effort of the National Oceanic and Atmospheric Administration (NOAA), NOAA’s National Weather Service, and their funded institutions. Oceanic and atmospheric conditions are updated weekly on the Climate Prediction Center web site (El Niño/La Niña Current Conditions and Expert Discussions). Forecasts for the evolution of El Niño/La Niña are updated monthly in the Forecast Forum section of CPC's Climate Diagnostics Bulletin. The next ENSO Diagnostics Discussion is scheduled for 6 December 2012. To receive an e-mail notification when the monthly ENSO Diagnostic Discussions are released, please send an e-mail message to: ncep.list.enso-update@noaa.gov."



Pacific ENSO Applications Climate (PEAC) Center
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Honolulu, HI 96822
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Web Master's email: peac@noaa.gov
Page Last Modified: January 15 2013 03:50:00 GMT

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