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PEAC Seasonal Sea Level Outlook


November - December - January  (NDJ) 2017

 

The following sections describe: (i) the Canonical Correlation Analysis (CCA)-based forecasts for the seasonal MEAN and MAXIMUM sea level anomaly in the NDJ season of 2017, and (ii) the monthly sea level anomaly observed in the previous season, August - September - October (ASO) of 2017. See Figure 2 at right for location of USAPI tide guage stations.

Note that 'anomalies' are defined as 'deviations or departures from the normal' using 1983-2001 mean sea level values computed at each station. Also, note that the forecasting technique used here does not account for sea level anomalies created by other atmospheric or geological cNDJitions such as tropical cyclones, storm surges or tsunamis.

(i) Seasonal Sea Level Outlook NDJ 2017

Based on the independent SST values observed in the ASO 2017 season, the resulting CCA model has been used to forecast the sea-level for the NDJ 2017 season (see Table 1).

tide station location
 
Table 1 : Forecasts of MEAN and MAX sea level anomaly in inches for NDJ 2017
 
Tide Gauge Station
Forecast Anomaly for NDJ 2017 (in inches)
 

MEAN
Deviation(1)

Standard Deviation 
NDJ season
MAX
Deviation (2)
Standard Deviation of NDJ season
Marianas, Guam
+4
3.5
+22
3.2
Malakal, Palau
+4
4.3
+41
4.3
Yap, FSM 1
+5
4.7
+34
4.7
Chuuk, FSM**
+5
*
+34
*
Pohnpei, FSM
+5
3.8
+36
3.9
Kapingamarangi, FSM
*
*
*
*
Majuro, RMI
+5
2.8
+45
3.5
Kwajalein, RMI
+4
3.2
+44
3.7
Pago Pago, American Samoa
+5
(0)
3.2
+32
(+27)
3.4
Honolulu, Hawaii
+3
1.8
+23
2.4
Hilo, Hawaii
+3
1.8
+26
2.3

+/- indicate positive anomaly (rise) and negative anomaly (fall) respectively. Note that any changes between (0~ ±1) inch is considered to be negligible. Also note that changes within the range of (+/-) 2 inches are unlikely to cause any adverse climatic impact. *** Guesstimated values, ** Data currently unavailable; Figures in parenthesis are year-to-year seasonal anomaly.

1: Difference between the mean sea level for the given month and the 1983 through 2001 mean sea level value at each station (seasonal cycle removed); 2: Same as 1 except for maxima; SD stands for standard deviations.

* In Pago Pago, There was a level shift (approximately 5 inches) in American Samoa at the time of September 2009 earthquake. So, -5 inches has been adjusted (shown in parenthesis) to the current tide-gauge values of Pago Pago. 

 

Forecasts for NDJ: PEAC-CCA(1) Statistical model is predicting 4-5 inches above normal sea levels with reasonably high skill for the whole USAPI region. Complementary to PEAC forecasts, some dynamical models are also predicted high sea levels. At two and four months lead (November–January), sea levels are likely to be above-normal (4-10 inches) for Majuro, Pohnpei, and Chuuk. It is uncertain whether the high sea levels will propagate as far west as Yap and Malakal. At longer ranges (> 5 months), dynamical models suggest likelihood of rising sea levels in parts of the South Pacific (including American Samoa).

However, contrary to our observations, the current PEAC forecasts displays less elevated sea level for the Hawaiian Islands. This is partly due to impact of a wind-forced equatorial Rossby wave that is not simulated by the statistical models.  In addition, Hawaii will again be affected by “King Tides” soon. Current forecasts indicate that the highest tides of the year (“king tides”) will occur again in the early mornings over a few days either side of November 6, December 4, and January 2.

(1)Chowdhury M. R., P-S Chu, Schroeder T, and Colasacco N (2007): Seasonal Sea-level Forecasts by Canonical Correlation Analysis – An Operational Scheme for the U.S-Affiliated Pacific Islands (USAPI), Int. J. Climatol  27:1389-1402.

 

 

(ii) Observed Monthly Sea Level Deviation in  ASO 2017

The monthly time series (ASO 2017) for sea-level anomaly has been taken from the UH Sea Level Center. 

Current Conditions: Atmospheric and oceanic signals are leaning towards La Niña. La Niña means higher-than-average sea level—currently all stations are 4-7 inches above normal. This could potentially impact islands with minor coastal flooding or salt water intrusions and increase vulnerability to flooding from storms or large waves.

 

Table 2 : Observed MEAN anomaly and MAX sea level in inches for ASO 2017

 
Tide Gauge Station
Observed MEAN Sea Level 
Anomaly
Observed MAX Sea Level
 
August
2017
September
2017
October
2017
Standard Deviation of the ASO mean
August
2017
September
2017
October
2017
Standard Deviation of the ASO max
Marianas, Guam
+9
+7
+6.3
4.4
+22(0)
+22(0)
+22(0)
3.9
Malakal, Palau
+1
+5
*
4.8
+37(1)
+39(3)
+41(5)
4.8
Yap, FSM
+6
+7
+7.3
4.8
+33(6)
+33(6)
+35(8)
5.3
Chuuk, FSM
+5
+4
+6
*
*
*
*
*
Pohnpei, FSM
+6
+6
*
4.8
+34(4)
+30(0)
*
4.8
Kapingamarangi +3 +4 +4.2 * +28(1) +26(-1) +26(-1) *
Majuro, RMI
+4
+6
*
3.6
+41(1)
+44(4)
*
3.8
Kwajalein, RMI
+5
+5
+5.8
3.8
+38(1)
+38(1)
+41(4)
3.9
Pago Pago, American Samoa
+9
(+4)
+9
(+4)
+10.2
(+5)
2.8
+33(0)
[28]
+32(-1)
[27]
+30(-3)
[25]
3.1
Honolulu, Hawaii
+8
+5
+4.8
1.7
+28(8)
+21(1)
+21(1)
2.4
Hilo, Hawaii
+6
+5
+6
1.9
+28(5)
+23(0)
+23(0)
2.4
Denotes where data is unavailable