Skip Navigation Links weather.gov 
NOAA logo-Select to go to the NOAA homepage National Weather Service Forecast Office   Select to go to the NWS homepage
Pacific ENSO Applications Climate Center
banner piece
  banner piece
Local forecast by
"City, St" or Zip Code
Pacific ENSO Update

1st Quarter, 2012 Vol. 18 No. 1


SEASONAL SEA LEVEL OUTLOOKS FOR THE U.S.-AFFILIATED PACIFIC ISLANDS


The following sections describe: (i) the Canonical Correlation Analysis (CCA) forecasts for seasonal (mean and maxima) sea-level deviations for the forthcoming seasons JFM (January-February-March), FMA (February-March-April), and MAM (March-April-May) of 2012, (ii) the observed monthly mean and maximum sea-level deviations for the season OND (October-November-December) 2011, (iii) forecast verifications for OND 2011 (observed/forecast values). Note that the 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’. (See Figure 2 at right for location of these stations.) Also note that, the CCA-forecasting technique adapted here accounts for ENSO-related sea-level deviations and does not account for sea-level deviations created by other atmospheric or geological factors such as tropical cyclones, storm surges or tsunamis.

tide station location
 

(i) Seasonal sea level forecast (deviations with respect to climatology) for JFM, FMA, and MAM of 2012

Forecasts of the mean and maximum sea-level deviations in the USAPI are presented using CCA statistical model. Based on the independent SST values in OND 2011, the resulting CCA model has been used to forecast the sea level of three consecutive three-month periods: JFM, FMA, and MAM of 2012 (see Table 1). CCA cross-validation forecast skills for 0, 1, and 2-month leads are presented in Fig. 3.

Table 1 : Forecasts of MEAN and MAXIMUM sea level deviation in inches for forthcoming seasons

 
(1) Seasonal Mean Deviations1
(2) Seasonal Maximum Deviations2
Tide Gauge Station
JFM
FMA
MAM

(3) Forecast Quality3

JFM
FMA
MAM
(3) Forecast Quality3
(4) RP for JFM Season4
(5) Lead Time5
0
1M
2M
0
1M
2M
20 yr
100 yr
Marianas, Guam
+6
+6
+6
Very Good
+21
+21
+21
Very Good
5.6
6.7
Malakal, Palau
+5
+5
+4
Very Good
+41
+41
+41
Good
9.6
14.3
Yap, FSM
+4
+4
+5
Very Good
+31
+33
+33
Good
16.7
33.0
Chuuk, FSM**
+5
+5
+5
N/A
+31
+33
+33
N/A
N/A
N/A
Pohnpei, FSM
+6
+6
+5
Very Good
+35
+34
+34
Very Good
5.8
7.1
Kapingamarangi, FSM
+6
+6
+5
Good
+31
+30
+30
Fair
7.4
9.4
Majuro, RMI
+4
+4
+3
Good
+44
+44
+43
Fair
4.1
5.1
Kwajalein, RMI
+3
+4
+4
Good
+42
+42
+42
Good
4.5
5.9
Pago Pago, AS
+4
+5
+5
Very Good
+29
+29
+29
Very Good
3.9
5.4
Honolulu, Hawaii
-1
-1
-1
Poor
+17
+16
+16
Poor
4.1
5.9
Hilo, Hawaii
-1
-1
-1
Good
+22
+20
+20
Fair
7.9
11.4

Remarks:

The forecasted values of sea level for JFM, FMA, and MAM seasons (Table 1, above) indicate that sea levels for some of the stations (i.e., Guam, Malakal, Yap, Pohnpei, and Kapingamarangi) are likely to be about 4-6 inches higher than normal in the forthcoming seasons. Other stations in the Marshalls (Majuro, Kwajalein) and American Samoa (Pago Pago) are also expected to be about 3-5 inches higher than normal.

These forecasts (e.g., higher than average sea level) are supportive to on-going La Niña condition. According to CPC’s ENSO Alert System Status, which has been marked as ‘La Niña Advisory’— La Niña is expected to continue into the Northern spring 2012. Collectively, the current oceanic and atmospheric anomalies reflect a moderate-to-weak strength La Niña. During any La Niña event the sea level in the USAPI region experiences a rise. However, the current La Nina is weakening now. As a result, a trend of gradual fall of sea level has been observed in the seasons FMA and MAM.

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; also note that any deviations from -1 to +1 inches are considered negligible and deviations from -2 to +2 inches are unlikely to cause any adverse climatic impact. Forecasts for Chuuk (**) are estimated subjectively based on information from WSO Chuuk and observations from neighboring stations of Pohnpei and Yap.

1 Seasonal Mean Deviations is defined as the difference between the mean sea level for the given month and the 1975-1995 mean sea level value at each station. Likewise, 2 Seasonal Maximum Deviations is defined as the difference between the maximum sea level (calculated from hourly data) for the given month and the 1975-1995 mean sea level value at each station.

3 Forecast Quality is a measure of the expected CCA cross-validation correlation skill. In general terms, these forecasts are thought to be of useful (but poor) skill if the CCA cross-validation value lies between 0.3 ~ 0.4 (Fig. 3). Higher skills correspond to a greater expected accuracy of the forecasts. Skill levels greater than 0.4 and 0.6 are thought to be fair and good, respectively, while skill levels greater than 0.7 are thought to be very good.

4 Return Period (RP) of extreme values is calculated from hourly sea-level data. For example, the predicted rise of 5.6 inches at 20-year RP at Marianas, Guam indicates that this station may experience an extreme tide event once every 20 years that could result in sea-level rise of up to 5.6 inches above the median of seasonal maxima during the JFM season. Likewise, about once every 100 years we can expect the highest OND tide at Marianas, Guam to be as high as 6.7 inches above the median of seasonal maxima. During some seasons some stations display alarmingly high values at the 20 and 100 year RP. These high values are due to large and significant increases in the tidal range caused by the passage of past storm events during that season. Click here to view probability of exceedence graphs for the JFM season.

5 Lead time is the time interval between the end of the initial period and the beginning of the forecast period. For example, lead-0, lead-1M, and lead-2M means ‘sea-level’ of target season 0 (JFM), 1 (FMA), and 2 (MAM) month leads based on SSTs of OND 2011.

 

(ii) Observed monthly sea level deviation in (OND) 2011 Season

The monthly time series for sea-level deviations have been taken from the UH Sea Level Center. Note that ‘deviation’ is defined here as ‘the observed or forecast difference between the monthly mean [or maximum] and the climatological monthly mean values (from the period 1975- 1995) computed at each station’. Locations of these stations can be found at: http://www.prh.noaa.gov/peac/map.php.

 

Table 2: Monthly observed MEAN and MAX sea level deviations in inches for October, November, and December, with year to year standard deviations (SD).

Tide Gauge Station

Monthly Mean Deviations 1
Monthly Maximum Deviations 2
Oct
Nov
Dec
SD
Oct
Nov
Dec
SD
Marianas, Guam
+6.7
+4.5
+3.3
4.0
+21
+19
+21
3.5
Malakal, Palau
+9.2
+8.1
+7.2
4.0
+47
+43
+42
4.1
Yap, FSM
+6.3
+3.7
+4.2
4.1
+36
+30
+35
4.1
Chuuk, FSM
*
*
*
*
*
*
*
*
Pohnpei, FSM
+8.2
+7.6
*
4.7
+40
+39
*
4.9
Kapingamarangi, FSM
*
*
*
3.1
*
*
*
3.8
Majuro, RMI
+8.6
+6.0
*
3.7
+48
+47
*
3.8
Kwajalein, RMI
+4.0
+0.5
+2.7
3.1
+44
+39
+43
3.2
Pago Pago, AS
+8.9
+8.6
*
2.5
+35
+33
*
2.2
Honolulu, Hawaii
+1.0
0.0
-2.3
1.8
+23
+19
+17
2.6
Hilo, Hawaii
+3.5
*
-1.2
1.8
+26
+24
+19
2.2

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. Standard deviations describe how widely spread the values are in the dataset. See Table 1 for other footnotes.

Remarks:

As compared to November 2011, the monthly mean sea level in December 2011 shows fall in all stations except Yap and Kwajalein. During the month of August 2011, sea level of all stations (except Kwajalein) recorded rise. In September, some stations recorded rise and others recorded fall. In October, most of the stations recorded a marginal fall while a few stations recorded marginal rise. In November and December most of the stations (except Yap and Kwajalein) recorded fall. Currently, all stations are 2 to 7 inches higher than normal. The monthly maxima also displayed a similar trend. Current elevated sea levels are supportive to on-going La Niña condition.

.

 

(iii) Forecast Verification (Seasonal Mean) for OND 2011

Observed and forecast seasonal sea level values for the OND 2011 season are presented in Figure 4. Forecasts were, in general, skillful. However, several stations are found to be under-forecasted. A probable reason was the recent trend of enhanced trade winds. Therefore, only SST-based sea-level forecasts are found to be less skillful in this season.

(iv) Tide Predictions (January 1 to March 31, 2012)

NOAA's web site for tide and currents has been used to generate the water level plot for the next three months. Predicted water level plots from Janury 1 to March 31, 2011 for five stations [(a) Marianas, Guam (b) Kwajalein, RMI (c) Pago Pago, American Samoa (d) Honolulu, Hawaii and (e) Hilo, Hawaii are provided below

 

Figure 5 (below): Predicted water level for the JFM 2011 season at (a) Marianas, Guam (b) Kwajalein, RMI (c) Pago Pago, American Samoa, (d) Honolulu, HI , (e) Hilo, Hawaii, and (f) Chuuk, FSM. Data from NOAA/NOA/CO-OPS. X-axis: date/time (GMT); Y-axis: height in feet relative to Mean lower low water level (MLLW); MR: Mean-difference between high and low; SR: Difference between high and low tide during full moon (spring tide); and ML: Arithmetic means of high and low tides.

 

Predicted Water Level Plot for Guam

a) Marianas, Guam

 

Predicted Water Level Plot for RMI

b) Kwajalein, RMI

 

Predicted Water Level Plot for American Samoa

c) Pago-Pago, American Samoa

 

Predicted Water Level Plot for Honolulu

d) Honolulu, Hawaii

 

Predicted Water Level Plot for Hilo

e) Hilo, Hawaii

 

Predicted Water Level Plot for Chuuk

e) Chuuk, FSM



Pacific ENSO Applications Climate (PEAC) Center
c/o NOAA NWS - Weather Forecast Office Honolulu
2525 Correa Road, suite 250
Honolulu, HI 96822
(808) 956-2324

Web Master's email: peac@noaa.gov
Page Last Modified: March 22 2012 05:05:12 GMT

Disclaimer
Credits
Glossary

Privacy Policy
About Us
Career Opportunities