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Pacific ENSO Update

2nd Quarter, 2011 Vol. 17 No. 2


La Niña became strong in the latter months of 2010, and continued to dominate the weather and climate of the Pacific basin through April 2011. There are signs (particularly in the sub-surface ocean) that the current La Niña is fading. The Climate Prediction Center anticipates a return to ENSO-neutral by July of 2011 (see CPC statement to the right). While the first half of 2010 was generally dry throughout the USAPI, as is typical in the year that follows El Niño, it has been very wet at many islands during the first three months of 2011 (see Figures 1a and 1b). The most notable exception to recent wet conditions occurred at islands along the equator where colder-than-normal SSTs accompanied exceptionally dry conditions. One such affected location was the island of Kapingamarangi, where extended dry conditions likely caused harm to water supplies, vegetation and crops. The following description appeared in a drought information statement issued by the Guam Weather Forecast Office (WFO) on 21 April 2011 (and in several earlier such statements): “Damage to food crops has likely occurred on Kapingamarangi atoll and the other drought stricken areas. The health of food crops should be closely monitored...and food assistance may be necessary if damage to plants and fruits is irreversible. Catchments should still be monitored in the coming weeks.”

It should be noted that rainfall amounts on Kapingamarangi have recently seen a substantial increase, and extremely dry conditions should subside as La Niña continues to fade.

Other islands affected by the equatorial cold tongue of water and its accompanying lack of rainfall include Nukuoro, Kosrae, Nauru, and the atolls of Kiribati. Rainfall at Nauru and throughout Kiribati was likely as severely reduced as at Kapingamarangi. Further north, at Nukuoro and at Kosrae, rainfall was low during several months, but was not as drastically reduced as at other islands closer to the equator. As a general rule, rainfall was more abundant further from the equator and further west. At islands that are well away from the equator, and that are normally in their dry season during the first three months of the year (e.g. Guam, the CNMI, and the northern RMI), rainfall was unusually abundant. Many locations in the state of Hawaii and in American Samoa were also wetter than normal during the first quarter of 2011, with the exception of the Big Island. Computer forecasts available to the PEAC Center largely anticipated this abundant rainfall, and most of the PEAC Center’s outlooks have reflected this.

The final quarter in 2010 and the first quarter of 2011 were generally wet for most of the islands in the state of Hawaii with the exception of the Big Island (see local summary for more information). This is a very welcome change to the drought conditions present during the second half of 2010 on all the islands. In fact, all drought conditions have been eliminated on Oahu and Kauai. Also, heavy rainfall this winter has diminished drought conditions across the central Hawaiian Islands, which is typical for a La Niña winter.

The following comments from the 07 April 2011 EL NIÑO/SOUTHERN OSCILLATION (ENSO) DIAGNOSTIC DISCUSSION were posted on the U.S. Climate Prediction Center web site:

“ENSO Alert System Status: La Niña Advisory.

Synopsis: A transition to ENSO-neutral conditions is expected by June 2011.

La Niña weakened for the third consecutive month, as reflected by increasing surface and subsurface ocean temperatures across the equatorial Pacific Ocean. All four Niño indices ranged between –0.3 °C and –0.8 °C at the end of March 2011. Subsurface oceanic heat content anomalies (average temperatures in the upper 300m of the ocean) became weakly positive in response to the continued eastward progression of a strong oceanic Kelvin wave, which has begun to shoal in the eastern Pacific. However, the basin wide extent of negative SST anomalies remained considerable throughout the month. Also, La Niña impacts on the atmospheric circulation remained strong over the tropical and subtropical Pacific. Convection remained enhanced over much of Indonesia and suppressed over the western and central equatorial Pacific. Also, anomalous low-level easterly and upper-level westerly winds have persisted in this region. Collectively, these oceanic and atmospheric anomalies reflect a weakening La Niña, but with ongoing global impacts. ...

La Niña will continue to have global impacts even as the episode weakens through the Northern Hemisphere spring. Expected La Niña impacts during AMJ 2011 include suppressed convection over the west-central tropical Pacific Ocean, and enhanced convection over Indonesia. ...

The next ENSO Diagnostics Discussion is scheduled for 5 May 2011. To receive an e-mail notification when the monthly ENSO Diagnostic Discussions are released, please send an e-mail message to:”

Pacific ENSO Applications Climate (PEAC) Center
c/o NOAA NWS - Weather Forecast Office Honolulu
2525 Correa Road, suite 250
Honolulu, HI 96822
(808) 956-2324

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Page Last Modified: May 20 2011 04:28:35 GMT


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