The necessary tools needed to classify a harbor according to this 
system are the following: 
(1) Mean air temperatures for each month, (Figures 1 to 12)* 
(2) Tide range tables or charts (Figure 13)** 
(3) Hydrographic charts or maps indicating the presence or absence 
of fresh water influence. 
*Mean air temperatures from Figures |] through 12 should be used 
only when a more detailed atlas or currentinformation are not available. 
Actual averages of air temperatures for two weeks to a month prior to 
the forecast date should be used whenever possible. U.S. Weather 
Bureau data and averaging techniques should give optimum results if 
the air temperature data are representative of the vicinity of the forecast 
point. Climatic data from U. S. Weather Bureau, foreign climatic 
tables and atlases, and ‘‘U. S. Navy Marine Climatic Atlases’’ (Vols. 
I-V) (reference no, 25) are recommended when current information is 
not available. 
**Figure 13 should be used when tide tables or suitable tide range 
analysis is not available. 
