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Pacific ENSO Update

2nd Quarter, 2012 Vol. 18 No. 2



La Niña was nearly over by mid-April 2012. At the time of this writing, La Niña had not officially been declared over by NOAA, but on the most recent (April 12th) regional PEAC conference call among the weather offices of the USAPI, NCEP, and IRI, it was suggested that this declaration would be forthcoming (see CPC statement below). The weather of the 1st Quarter of 2012 was generally very tranquil throughout the USAPI, with the exception of Hawaii, where an extreme storm on March 9 brought very heavy rainfall, high winds, hail, and a weak tornado (see the State of Hawaii discussion below and on page 9). No significant tropical cyclone activity occurred in Micronesia or American Samoa during the 1st Quarter of 2012. While rainfall was near normal at many islands, some islands experienced notable dryness during certain months and for the whole 1st Quarter (see FIGURE 1). Although Guam and the CNMI had above average rainfall for the 1st quarter, these locations have recently been experiencing periods of very low rainfall totals. The vegetation on these islands has become wilted and brown, and several wildfires were observed on Guam.

Other islands affected by recent dry spells include some of the northern islands of Chuuk State, Pohnpei Island and the eastern islands of Pohnpei State, Kosrae, and some of the northern atolls of the RMI. While recent dryness on Pohnpei Island has caused many residents to be concerned, it is anticipated that abundant rainfall should return within a few weeks to most of Pohnpei State.

Hawaii weather during the month of January 2012, was generally uneventful. Trade winds kept the islands with sufficient amounts of rainfall, while some areas remained in a drought state. These drought conditions still persist on Molokai and Maui although they did receive some relief. The Big Island maintains a large contrast form the plush windward areas and the drought-ridden Kahala district, north and south Kona districts, and the Hamakua district.

The State of Hawaii experienced a severe thunderstorm event on Friday, March 9th, associated with a cutoff upper-level low. A 4.25 inch hailstone was recorded in Kaneohe on Oahu, which is a new state record. Additionally, an EF-0 tornado with winds of 60-70 mph touched down near Lanikai on Oahu. This event brought significant 24-hour rainfall totals to the islands, including 11.14 inches at the Oahu Forest National Wildlife Refuge, 8.71 inches at Hanalei on Kauai, and 7.90 inches at Puu Kukui on Maui. The National Weather Service in Honolulu monitored the situation closely, and the response to this significant severe weather event was considered a success.

The following comments from the 05 April 2012 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: La Niña is expected to transition to ENSO-neutral conditions during April 2012.

La Niña continued to weaken during March 2012, as below-average SSTs persisted primarily in the central Pacific. All of the Niño indices have warmed considerably during the last two months, and the Niño 4 and Niño 3.4 indices averaged only near -0.5 in March. The oceanic heat content (average temperature in the upper 300m of ocean) anomalies also continued to warm, with alternating pockets of negative and positive temperature anomalies observed within the upper 100 m in the central and eastern Pacific. Significant anomalous low-level westerly winds developed in the western tropical Pacific in late March, associated with the MJO. This wind event could further warm the central and eastern Pacific within the coming few months. Presently, however, the larger scale atmospheric circulation anomalies and the Southern Oscillation Index retain their La Niña characteristics. Accordingly, convection remains suppressed in the western and central Pacific, and enhanced over Indonesia, Malaysia and the Philippines. Collectively, these oceanic and atmospheric patterns indicate that a transition from La Niña to ENSO-neutral conditions is underway.

A majority of models predict ENSO-neutral conditions for March-April-May, continuing through the Northern Hemisphere summer 2012. Based on the continued weakening of the negative SST anomalies during March , as well as the historical tendency for La Niña to dissipate during the Northern Hemisphere spring, we continue to expect a weakening La Niña during April. ENSO-neutral conditions are then expected to persist through the summer. Thereafter, there is considerable uncertainty in the forecast, which slightly favors ENSO-neutral or developing El Niño conditions over a return to La Niña conditions during the remainder of 2012.”

Pacific ENSO Applications Climate (PEAC) Center
c/o NOAA NWS - Weather Forecast Office Honolulu
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Honolulu, HI 96822
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Page Last Modified: June 08 2012 05:44:07 GMT


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