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PEAC Seasonal Sea Level Outlook


April - May - June  (AMJ) 2018

 

The following sections describe: (i) the Canonical Correlation Analysis (CCA)-based forecasts for the seasonal MEAN and MAXIMUM sea level anomaly in the AMJ season of 2018, and (ii) the monthly sea level anomaly observed in the previous season,  January - February - March (JFM) of 2018. 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 conditions such as tropical cyclones, storm surges or tsunamis.

(i) Seasonal Sea Level Outlook AMJ 2018

Based on the independent SST values observed in the JFM 2018 season, the resulting CCA model has been used to forecast the sea-level for the AMJ 2018 season (see Table 1).

tide station location
 
Table 1 : Forecasts of MEAN and MAX sea level anomaly in inches for AMJ 2018
 
Tide Gauge Station
Forecast Anomaly for AMJ 2018 (in inches)
 

MEAN
Deviation(1)

Standard Deviation 
AMJ season
MAX
Deviation (2)
Standard Deviation of AMJ season
Marianas, Guam
+6
4.4
+22
4.0
Malakal, Palau
+4
5.3
+41
5.3
Yap, FSM 1
+6
4.9
+34
5.2
Chuuk, FSM**
+4
*
+34
*
Pohnpei, FSM
+5
3.6
+36
3.5
Kapingamarangi, FSM
+7
*
*
*
Majuro, RMI
+5
2.4
+45
2.7
Kwajalein, RMI
+5
3.1
+44
3.4
Pago Pago, American Samoa
+8
(+2)
3.3
+32
(+27)
3.8
Honolulu, Hawaii
+3
1.6
+23
2.4
Hilo, Hawaii
+2
2.0
+26
3.0

+/- 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. *** (Experimental) Satellite Aviso Altimetry data, ** 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 AMJ: PEAC-CCA[1] Statistical model is predicting 1-7 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 during the next three months. According to UHSLC forecasts (see https://uhslc.soest.hawaii.edu/sea-level-forecasts/), at longer leads (four to six months) these models suggest an increase in sea levels (likely exceeding 6 inches/15 cm above-normal for Majuro, Pohnpei, and Chuuk). Sea levels are predicted to gradually lower around Hawaii

 

[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  JFM 2018

The monthly time series (JFM 2018) for sea-level anomaly has been taken from the UH Sea Level Center. 

Current Conditions Atmospheric and oceanic signals are leaning towards weak La Niña. La Niña means higher-than-average sea level—currently all stations are 4-10 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 JFM 2018

 
Tide Gauge Station
Observed MEAN Sea Level 
Anomaly
Observed MAX Sea Level
 
January
2018
February
2018
March
2018
Standard Deviation of the JFM mean
January
2018
February
2018
March
2018
Standard Deviation of the JFM max
Marianas, Guam
+8
+7.5
+8
4.4
+25(3)
+24
+23
4.0
Malakal, Palau
+3
+1.5
+6
5.3
+39(3)
+39
+41
5.3
Yap, FSM
+9.5
+8.5
+7
4.9
+37(9)
+35
+35
5.2
Chuuk, FSM
+6
+3.8
+5.2
**
**
**
**
**
Pohnpei, FSM
+10
+8.5
+6.2
3.6
**
**
+34(4)
3.5
Kapingamarangi ** +9 +7.5 ** +38 +38 +29 **
Majuro, RMI
+10.5
+8.8
+5
2.4
**
**
+45(5)
2.7
Kwajalein, RMI
+9
+7
+4.4
3.1
+47(10)
+47
+46
3.4
Pago Pago, American Samoa
+11.5
(+6.5)
+10.5
(+5.5)
+10.5
(+5.5)
3.3
+38(5)
[33]
+38
+34
3.8
Honolulu, Hawaii
+4.7
+3
+2
1.6
+27(7)
+25
+18
2.4
Hilo, Hawaii
+.35
+4
+1
2.0
+31(8)
+29
+21
3.0
** Denotes where data is unavailable