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PEAC Seasonal Sea Level Outlook


June - July - August (JJA) 2018

 

The following sections describe: (i) the Canonical Correlation Analysis (CCA)-based forecasts for the seasonal MEAN and MAXIMUM sea level anomaly in the JJA season of 2018, and (ii) the monthly sea level anomaly observed in the previous season,  March - April - May (MAM) 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 JJA 2018

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

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

MEAN
Deviation(1)

Standard Deviation 
JJA season
MAX
Deviation (2)
Standard Deviation of JJA season
Marianas, Guam
+2
3.5
+20
4.6
Malakal, Palau
-3
4.4
+33
4.4
Yap, FSM 1
-1
3.9
+27
3.9
Chuuk, FSM**
+1
**
+28
**
Pohnpei, FSM
0
2.5
+29
3.3
Kapingamarangi, FSM
0
**
+28
**
Majuro, RMI
0
2.0
+40
2.6
Kwajalein, RMI
0
2.6
+38
3.0
Pago Pago, American Samoa
+7
(+2)
4.2
+34
(+29)
3.7
Honolulu, Hawaii
+2
1.7
+23
2.3
Hilo, Hawaii
+2
1.9
+26
2.6

+/- 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 ( ) for monthly-max anomaly indicates difference between the maximum anomaly for the given month and the long-term monthly average anomaly.

1: Difference between the mean sea level for the given month and the 1983 through 2001 monthly 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 JJA: PEAC-CCA Statistical model is predicting normal to marginally below-normal in the forthcoming JJA-ASO seasons. If El Niño develops as per projections, then the lowest anomalies of sea level may likely to occur at the later part of 2018. In Hawaii, both Honolulu and Hilo are likely to be slightly elevated, but still close to normal.  Note that the south Pacific station (i.e., Pago Pago) maintains a 4-6 months’ time-lag to change fall/rise when compared to north Pacific stations (i.e., Guam and the Marshalls).

 

[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  MAM 2018

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

Current Conditions

All stations displayed considerably above normal sea level during JFMA. However, in April, sea level started to fall. Some of the stations may still remain marginally elevated in June, but likely to fall below normal in July or August 2018. Hawaii sea levels also returned to normal, but Hilo recorded some considerable rise in May.

Impacts: Tides have been very high with high waves all over Micronesia and Marshalls Islands during JFMA. Most of the events were associated with northerly swell from northern Pacific storm. There have been regular minor-to-moderate inundations in low-lying atolls and Pohnpei, Kosrae, and Chuuk reported road damage during this quarter.

 

 

Table 2 : Observed MEAN anomaly and MAX sea level in inches for MAM 2018

 
Tide Gauge Station
Observed MEAN Sea Level 
Anomaly
Observed MAX Sea Level
 
March
2018
April
2018
May
2018
Standard Deviation of the MAM mean
March
2018
April
2018
May
2018
Standard Deviation of the MAM max
Marianas, Guam
+8
+6
+4
3.9
+23
+20
+18
4.0
Malakal, Palau
+6
0
-4
4.2
+41
+37
+31
4.3
Yap, FSM
+7
+6
+4.5
4.5
+35
+32
+29
5.0
Chuuk, FSM
+5.2
+2.8
+2
*
**
**
**
**
Pohnpei, FSM
+6.2
+4.6
0
2.6
+34
+32
+29
2.9
Kapingamarangi +7.5 +6.6 +6.6 ** +29 +28 +31 **
Majuro, RMI
+5
+5
+3
2.0
+45
+43
+40
3.0
Kwajalein, RMI
+4.4
+1.7
0
2.6
+46
+36
+36
3.3
Pago Pago, American Samoa
+10.5
(+5.5)
+10.5
(+5.5)
+11
(+6)
4.2
+34
+31
+31
4.8
Honolulu, Hawaii
+2
+2
+1.5
1.7
+18
+16
+20
1.9
Hilo, Hawaii
+1
+3.5
+5
1.9
    +21
+23
+26
2.4
** Denotes where data is unavailable