NEW - Experimental Sea level Forecasts
(deviations w. r. t. climatology) for the U.S-affiliated Pacific Islands

In addition to seasonal rainfall forecasts, there is a strong demand for sea level forecasts with a lead time of a season or longer in the US-affiliated Pacific Islands (USAPI). This demand was raised by the representatives of the user community in the last Pacific ENSO Applications Center (PEAC) review meeting held in Honolulu, Hawaii (USA) June 1-3, 2004 (a draft summary at http://research.eastwestcenter.org/climate/PEAC/). In order to address this need, PEAC developed an experimental statistical sea level forecast which predicts seasonal sea level deviations from mean sea level one to two months in advance.

In this issue of newsletter, we introduce an experimental statistical forecasting model using Canonical Correlation Analysis (CCA). This statistical sea level forecast is based on the teleconnections, or air-sea interactions over great distances, between tropical SST and sea level in the USAPI. This CCA model predicts the seasonal sea level variability in real-time at a considerably long lead-time (one to two months). Results have been found to be skillful.

Observed monthly sea level deviation in JFM, 2005

This following Table 4 contains monthly values of sea level deviations as reported from the UH Sea Level Center from January to March 2005. Units for the sea level deviations are in centimeters. Deviations are defined here as the difference between the mean sea level for the given month and the 1975 to 1995 mean sea level at that station. The full time series is available at: http://ilikai.soest.hawaii.edu/uhslc/woce.html

With the exception of Guam in March (which had a sharp rise), a negative deviation was recorded in most of the northwestern Pacific Islands (i.e., Saipan, Malakal, and Yap) from January to March, 2005. In contrast, the low latitude Pacific Islands (i.e., Pohnpei, Kapingamarangi) and the central Pacific islands (i.e., Majuro and Kwajalein) had a positive deviation during the same time period. The sea level of the lone south Pacific station, American Samoa (Pago-Pago) displayed a slightly positive deviation in Jan and Feb; however, in March, a sharp drop is observed (Table 4). Consistent to the monthly sea level variations, the seasonal average sea level deviation of January-February-March (JFM) also displayed similar variations (Fig. 3).

This quarter (JFM) had more significant variations than the last quarter (October-November-December) of 2004. During October November December (OND) 2005, the average sea-level deviations in most of the tide gauge stations remained close to normal. In contrast during JFM 2005, a negative deviation (lower than long term average sea level) was observed in the northwest Pacific while a positive deviation (higher than long term average sea level) was observed in the region of central to southern Pacific.

Seasonal Sea Level Forecast for AMJ, MJJ, and JJA, 2005

The deviations of sea level are relatively small at the present time, but are consistent with a weak El Niño pattern that is gradually weakening. As the El Niño condition is gradually weakening, the sea level variation may not display any significant variations during the 2nd quarter of 2005.

Table 5 : Forecasts of sea level deviation in cm (AMJ: April-May-June, MJJ: May-June-July, and JJA: June-July-August)