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PEAC Seasonal Sea Level Outlook


 July - August - September (JAS) 2017

 

The following sections describe: (i) the Canonical Correlation Analysis (CCA)-based forecasts for the seasonal MEAN and MAXIMUM sea level anomaly in the JAS season of 2017, and (ii) the monthly sea level anomaly observed in the previous season, April - May - June (AMJ) 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 conditions such as tropical cyclones, storm surges or tsunamis.

(i) Seasonal Sea Level Outlook JAS 2017

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

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

MEAN
Deviation(1)

Standard Deviation 
JAS season
MAX
Deviation (2)
Standard Deviation of JAS season
Marianas, Guam
+3
3.6
+20
3.4
Malakal, Palau
+2
4.5
+40
4.6
Yap, FSM 1
+3
4.8
+32
4.2
Chuuk, FSM**
+3
--
+32
*
Pohnpei, FSM
+3
3.4
+32
3.3
Kapingamarangi, FSM
*
*
*
*
Majuro, RMI
+4
2.5
+44
3.2
Kwajalein, RMI
+3
3.0
+42
3.5
Pago Pago, American Samoa
+5
(0)
3.4
+31
(+26)
3.6
Honolulu, Hawaii
+3
1.8
+21
2.3
Hilo, Hawaii
+2
1.8
+24
2.4

+/- 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 JAS: Sea levels are generally predicted to hold constant over the next three months for most of the tropical Pacific. At three months lead (July–September), sea levels are likely to be above-normal (2-4 inches) for Majuro, Pohnpei, Chuuk, Yap, and Malakal. Near-normal sea levels are expected to continue around American Samoa.

Elevated sea levels around Hawaii are likely to slowly diminish through the forecast period, potentially enhancing extreme high tides during July, similar to observed in  May.

 

(ii) Observed Monthly Sea Level Deviation in  AMJ 2017

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

Current ConditionsMost of the stations in north and south Pacific recorded considerable fall in February-April, reaching closer to normal.  A combination of the highest astronomical tides of the year ("King Tides"), global sea level rise, delayed sea level effects from the 2014-2016 El Niño, Pacific-wide climate and sea level variability, and localized eddies have caused record-breaking sea level heights in HawaiĘ»i in MAY. The Flooding and wave inundation have occurred in many parts of the state at the end of April and May, in particular when large swell events coincide. However, the height of king-tides receded in JUNE and no major inundation was observed.

 

 

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

 
Tide Gauge Station
Observed MEAN Sea Level 
Anomaly
Observed MAX Sea Level
 
April 2017
May
2017
June
2017
Standard Deviation of the AMJ mean
April
2017
May
2017
June
2017
Standard Deviation of the AMJ max
Marianas, Guam
+4
+6
+5
3.6
+20
+23
+22
3.4
Malakal, Palau
+1
+1
+1
4.3
+39
+38
+37
4.6
Yap, FSM
+5
+6
+7
4.2
+35
+36
+37
4.2
Chuuk, FSM
+4
+4
+4
*
*
*
*
*
Pohnpei, FSM
+4
+5
**
2.7
+31
+34
**
3.3
Majuro, RMI
+5
+4
**
2.2
+45
+45
**
3.2
Kwajalein, RMI
+3
+3
+3
2.7
+42
+41
+40
3.5
Pago Pago, American Samoa
+10
(+5)
+10
(+5)
+10
(+5)
4.5
+33
+34
+33
3.6
Honolulu, Hawaii
+8
+8
+5
2.0
+28
+29
+29
2.3
Hilo, Hawaii
+6
+7
+4
2.2
+28
+31
+28
2.4
Denotes where data is unavailable