Remarks: The positive sea-level deviations forecast for the JAS, ASO, and SON seasons (Table 1, above) indicate that sea levels will remain slightly elevated at all USAPI and Hawaii stations for another 1 to 3 months. From JAS to SON 2008, mean sea-levels are expected to begin receding back toward normal levels, consistent with the recent transition from La Niña to ENSO neutral conditions. Mean and maximum sea-levels are expected to be about 0 to 3 inches above median values (in parentheses) at each station during the JAS season.

Note: (-) indicates negative deviations (fall of sea level from the mean), and (+) indicates positive deviations (rise of sea level from the mean); N/A: data not available. Deviations from -1 to +1 inch are considered negligible (***) and unlikely to cause any adverse climatic impact. Forecasts for Chuuk (**) are estimated subjectively based on information from WSO Chuuk and observations from neighboring stations of Pohnpei and Yap.

(1) Median values (in parentheses) of mean and maximum sea-level deviations for the JAS season. The median is the 50th percentile value (or middle value) in the distribution of observed values.

(2) Seasonal Mean Deviations is defined as the difference between the mean sea level for the given month and the 1975-1995 mean sea level value at each station. Likewise, Seasonal Maximum Deviations (3) is defined as the difference between the maximum sea level (calculated from hourly data) for the given month and the 1975-1995 mean sea level value at each station.

(4) Forecast Quality is a measure of the expected CCA cross-validation correlation skill. In general terms, these forecasts are thought to be of useful (but poor) skill if the CCA cross-validation value lies between 0.3 ~ 0.4 (Fig. 3). Higher skills correspond to a greater expected accuracy of the forecasts. Skill levels greater than 0.4 and 0.6 are thought to be fair and good, respectively, while skill levels greater than 0.7 are thought to be very good.

(5) Return Period (RP) of extreme values is calculated from hourly sea-level data. For example, the predicted rise of 6.2 inches at 20-year RP at Marianas, Guam indicates that this station may experience an extreme tide event once every 20 years that could result in sea level rise of up to 6.2 inches above the median of seasonal maxima during the JAS season. Likewise, about once every 100 years we can expect the highest JAS tide at Marianas, Guam to be as high as 10.8 inches above the median of seasonal maxima. During some seasons some stations display alarmingly high values at the 20 and 100 year RP. These high values are due to large and significant increases in the tidal range caused by the passage of past storm events during that season. Click here to view probability of exceedence graphs for the JAS season.

(6) Lead time is the time interval between the end of the initial period and the beginning of the forecast period. For example, lead-0, lead-1M, and lead-2M means ‘sea-level’ of target season 0 (JAS), 1 (ASO), and 2 (SON) month leads based on SSTs of AMJ 2008.

(7) Hawaii stations of Honolulu and Hilo are newly added and should be considered experimental. Any feedback regarding the usefulness of these forecasts will be appreciated.

Tide Gauge Station

Note: - indicate negative deviations (fall of sea-level from the mean), and + indicate positive deviations (rise of sea-level from the mean); N/A: data not available. ** Sea level data for Chuuk is based on estimates from neighboring tide stations (Yap and Pohnpei) and observations from WSO Chuuk. Standard deviations describe how widely spread the values are in the dataset. See Table 1 for other notes.

Remarks: The observed values for seasonal mean/maxima displayed positive deviation in all the USAPI stations during April-June 2008; the Hawaiian stations were also slightly elevated during this period. As expected, none of the stations recorded any considerable rise or fall in June for either the mean or maximum values. This trend is consistent with the transition phase from La Niña to ENSO-neutral conditions.

Figure 5 (below): Predicted water level for the JAS 2008 season at (a) Marianas, Guam (b) Kwajalein, RMI and (c) Pago Pago, American Samoa. Data from NOAA/NOA/CO-OPS. X-axis: date/time (GMT); Y-axis: height in feet relative to Mean lower low water level (MLLW); MR: Mean-difference between high and low; SR: Difference between high and low tide during full moon (spring tide); and ML: Arithmetic means of high and low tides.

a) Marianas, Guam (MR: 1.6 ft, SR: 2.4 ft, and ML: 1.4 ft)

b) Kwajalein, RMI (MR: 3.6 ft, SR: 3.9 ft, and ML: 1.9 ft )

c) Pago-Pago, American Samoa (MR: 2.5 ft, SR: 2.7 ft, and ML: 1.3 ft )