Pacific ENSO Update4th Quarter, 2005 Vol. 11 No. 4 |
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NEW - Experimental Sea level Forecasts
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Tide Gauge Station | OND | NDJ | DJF | Forecast quality1 | 1. Forecast quality is a measure of the expected CCA cross-validation correlation skill. In general terms, these forecasts are thought to be of useful skill (or at least fair skill) if the CCA cross-validation value is greater than 0.3 (Fig. 4). Higher skills correspond to greater expected accuracy of the forecasts. Skill levels greater than 0.4 and 0.5 are thought to be moderate and good, while skill levels greater than 0.6 and 0.8 are thought to be strong and very strong respectively. |
Lead Time2 | 0 | 1M | 2M | ||
Guam | ** | ** | ** | Good | |
Saipan | ** | -1 | -1 | Good | |
Malakal | +1 | ** | -2 | Very Strong | |
Yap | ** | -1 | -1 | Strong | |
Pohnpei | +2 | +1 | +2 | Very Strong | |
Kapingamari | +3 | +3 | +3 | Strong | |
Majuro | +2 | +2 | +2 | Strong | |
Kwajalein | ** | ** | ** | Strong | |
Pago Pago | +2 | +2 | +2 | Good | |
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 of +/-1 in. are considered negligible and denoted by **. Deviations +/- 2 in. are unlikely to cause any adverse impact. Using a historical perspective, during OND 1997 and 1998, Yap recorded 8.6 inches of negative and 6.3 inches of positive deviations respectively. Pago-Pago recorded 1.5 inches of positive and 3.4 inches of negative deviations during the same period. |
Observed monthly sea level deviation in JFM, 2005
The monthly time series (July to August) for sea level deviations have been taken from the UH Sea Level Center. The full time series (in mm) is available at ftp://ilikai.soest.hawaii.edu/islp/slpp.deviations. Deviations are defined here as the difference between the mean sea level for the given month and the 1975 through 1995 mean sea level value computed at each station.
Table 2 provides the monthly observed sea level deviations (in inches). All tide gauge stations recorded positive deviations in this quarter (3rd quarter) with Guam and Yap recording considerable positive deviations last quarter. As in previous quarters (JFM and AMJ), Guam continued to show sharp rise in this quarter too. The month of July and August displayed 12.3 and 10.5 inches of rise from the mean respectively (see Table 2 and Fig. 5; sea level data for the month of September is not available from the UH sea level center at print time). Malakal and Pohnpei recorded marginal to moderate positive deviations. Malakal initially remained steady in July, however, considerable variations were observed in August. Similarly, Kapingamarangi, Majuro and Kwajalein also provided positive deviations during the same time period. The sea level of the lone south Pacific station (American Samoa at Pago-Pago) displayed a rise during the same time period.
In last quarter’s issue, we forecasted positive deviations for all the tide gauge stations in JAS ( Fig. 5 dotted line). Real-time observed sea level data in JAS provided a very close match with the forecast values ( Fig. 5). All the observed values, except Guam and Yap, remained very close to the forecast ones. The deviations of Guam and Yap were considerably higher than the forecast values captured by CCA model simulation for prediction in JAS.
The relationship between the sea level and the SST time-series at each geographical grid-point has been investigated (figures are not reported here). Observations revealed, for example, the JAS sea level in Guam displays strong and positive correlations with the SSTs of the preceding and current season in the western Pacific. This positive correlation implies that warmer sea waters and more heat content with a deeper thermocline in the western North Pacific correspond to a higher sea level in Guam.
Table 2 : Monthly observed sea level deviations in inches (std deviation in parentheses)
Tide Gauge | July | August | September3 | |||
Deviation | SD | Deviation | SD | Deviation | SD | |
Guam | +9.4 | (4.6) | +10.9 | (4.6) | N/A | (4.6) |
Saipan | N/A | (2.9) | N/A | (2.4) | N/A | (3.1) |
Malakal | 0 | (4.4) | +4.1 | (4.2) | N/A | (4.3) |
Yap | +9.2 | (4.6) | +9.7 | (4.1) | N/A | (4.6) |
Kwajalein | +4.6 | (2.2) | +3.5 | (2.0) | N/A | (2.7) |
Majuro | +1.1 | (2.2) | +1.1 | (2.2) | N/A | (3.2) |
Pohnpei | +3.3 | (2.7) | +0.9 | (2.7) | N/A | (3.7) |
Kapingamar. | +1.7 | (2.3) | +2.2 | (2.5) | N/A | (2.6) |
Pago Pago | +1.7 | (3.1) | +3.7 | (2.8) | N/A | (2.6) |
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, Figures in parenthesis are year-to-year SD (standard deviations) for the month. 3. September data is unavailable at print time. |