Canonical correlation analysis (CCA) is used here to predict the SST adjacent to the U.S. coast around Hawaii, the mainland West Coast, the Gulf of Mexico coast and the Southeast Coast. Coastal SST forecasts are provided for commercial fishing interests as well as tourists (e.g. bathers and surfers). As described in several other articles in this Bulletin, CCA identifies linear relationships between multicomponent predictors and multicomponent predictands. In the present application, fields of near-global SST, Northern Hemisphere 700 mb height and the coastal SST predictand itself are used as predictors, covering four consecutive 3-month periods ending at the time of the forecast. To prevent overfitting in the weaker predictors, the SST field is weighted double on entry to the analysis, following standardization. The predictand is the coastal SST at various 3-month periods following the time of the forecast, ranging from zero lead (beginning at forecast time) out to a year ahead. The predictand SST is presented in 2^o x 2 ^o boxes, using COADS data from 1955 to 1979 and optimum interpolation data from 1990 to the present. The predictor and predictand data are filtered separately using standard EOF analyses prior to the CCA, as done originally by Barnett and Preisendorfer (1987) and in subsequent applications such as Graham et al. (1987a,b), Barnston and Ropelewski (1992), Barnston (1994), He and Barnston (1996), Shabbar and Barnston (1996) and Johansson et. al (1997).

The expected skill of the forecasts was estimated using cross-validation, in which each year in turn was held out of the model development sample and used as the forecast target. Figure 1 shows the seasonal cycle of areal average skill of the SST forecasts (temporal correlation between forecasts and observations), for (a) the West Coast of the mainland U.S., (b) the Gulf of Mexico and Southeastern coasts, and (c) the Hawaiian coasts. The 3-month target period is shown on the horizontal axis by the middle month number. Skills for five lead times are shown, as labeled in months. A 1-month lead indicates a forecast whose 3-month target period begins 1 month after the time of the forecast. Moderate skills are found for the SST along the West Coast for the cold half of the year for leads of up to 4 months, and for the Gulf/Southeast coasts for all seasons except winter at short leads and for late summer/early fall at both short and long leads. In the Hawaiian region skills are relatively lower. CCA skills are higher than the skill of persistence forecasts (with respect to the fourth of the four predictor periods), except for the Hawaiian skills for 1-month lead which are actually lower than persistence skills in the fall.

The top panel of Fig. 2 shows the geographical distribution of skill for Jan-Feb-Mar forecasts at 1 month lead. Skill is moderately high along the west U.S. coast, modest in the eastern Gulf of Mexico and along the east coast of Florida, and low around most of Hawaii. The bottom panel shows the loading pattern of the predictand for CCA mode 1 for this same forecast. The predictor loading pattern for this mode (not shown) clearly indicates the development of a cold ENSO episode during the summer and fall of the previous year. The predictand pattern shows that the SST anomalies associated with a cold ENSO Jan-Feb-Mar: negative anomalies along the West Coast, positive anomalies in the Gulf of Mexico and Southeast Coast, and negative (positive) anomalies in southern (northern) Hawaii. The fact that Hawaii lies in a south-north transition zone with respect to ENSO-related anomalies leads to lower predictive skill there, since it cannot benefit greatly from knowledge about the likely ENSO state as can many of the other coastal regions examined here.

Figure 3 shows the coastal SST forecasts for Jan-Feb-Mar (top) and Jun-Jul-Aug (bottom) of 1997, made in mid-December 1996. For Jan-Feb-Mar weak negative anomalies are forecast for the West Coast of the U.S. with moderate skill. Negative anomalies in this region are already in place in mid-December, and are related to the cool ENSO episode throughout 1966. In the Gulf of Mexico, the Southeast Coast and Hawaii, mainly weak anomalies are forecast with low skill. The forecast for Jun-Jul-Aug features warmth in the Gulf of Mexico with highest skill in the eastern Gulf and near southern Florida. With lower skill, positive anomalies are also suggested in portions of the West Coast and northern Hawaii.

Barnett, T.P. and R. Preisendorfer, 1987: Origins and levels of monthly and seasonal forecast skill for United States surface air temperatures determined by canonical correlation analysis. Mon. Wea. Rev., 115, 1825-1850.

Barnston, A.G., 1994: Linear statistical short-term climate predictive skill in the Northern Hemisphere. J. Climate, 7, 1513-1564.

Barnston, A.G. and C.F. Ropelewski, 1992: Prediction of ENSO episodes using canonical correlation analysis. J. Climate, 5, 1316-1345.

Barnston, A.G. and Y. He, 1996: Skill of CCA forecasts of 3-month mean surface climate in Hawaii and Alaska. J. Climate, 9, 2579-2605.

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Fig. 1. Seasonal cycle of cross-validated areal average skill of coastal SST forecasts using CCA, expressed as a temporal correlation between forecasts and observations, for (a) the West Coast of the mainland U.S., (b) the Gulf of Mexico and Southeastern coasts, and (c) the Hawaiian coasts. The 3-month target period is shown along the x-axis by the number of the middle month. Skills for five lead times are shown, as labeled in each panel. (Example: a 1-month lead indicates a forecast whose 3-month target period begins 1 month after the time of the forecast).

Fig. 2. Locations of the 2^o x 2^o SST boxes are indicated by the numerals on these two maps. The top panel shows the distribution of cross-validated forecast skill (correlation X100) for Jan-Feb-Mar forecasts made at 1 month lead. The bottom panel shows the CCA loading pattern for mode 1 for predicting Jan-Feb-Mar SST at 1 month lead. Units (X100) are relative; values of absolute value 0.6 or more are considered high; 1.0 is upper limit in absence of instability related to excessive colinearity.

Fig. 3. Forecast for coastal SST for Jan-Feb-Mar (top) and Jun-Jul-Aug (bottom) 1997 made at 0.5 and 5.5 months lead, respectively. Value of numbers shows uninflated standardized SST anomaly (X100) with respect to the 1961-1990 mean, and the physical size of numerals indicates estimated skill level (correlation) in three categories: blank for skill < .30, small for .30 < skill < .45, medium for .45 < skill < .60, and large for skill > .60.

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