HIGHER HIGH WATER (HHW). The higher of the two high waters of any tidal 

 day. The single high water occurring daily during periods when the tide 

 is diurnal is considered to be a higher high water. (See Figure A-10.) 



HIGHER LOW WATER (HLW). The higher of two low waters of any tidal day. (See 

 Figure A-10.) 



HINDCASTING, WAVE. The use of historic synoptic wind charts to calculate 

 characteristics of waves that probably occurred at some past time. 



HOOK. A spit or narrow cape of sand or gravel which turns landward at the 

 outer end. 



HURRICANE. An intense tropical cyclone in which winds tend to spiral inward 

 toward a core of low pressure, with maximum surface wind velocities that 

 equal or exceed 33.5 meters per second (75 mph or 65 knots) for several 

 minutes or longer at some points. TROPICAL STORM is the term applied if 

 maximum winds are less than 33.5 meters per second. 



HURRICANE PATH or TRACK. Line of movement (propagation) of the eye through an 

 area. 



HURRICANE STAGE HYDROGRAPH. A continuous graph representing water level 

 stages that would be recorded in a gage well located at a specified point 

 of interest during the passage of a particular hurricane, assuming that 

 effects of relatively short-period waves are eliminated from the record by 

 damping features of the gage well. Unless specifically excluded and 

 separately accounted for, hurricane surge hydrographs are assumed to 

 include effects of astronomical tides, barometric pressure differences, 

 and all other factors that influence water level stages within a properly 

 designed gage well located at a specified point. 



HURRICANE SURGE HYDROGRAPH. A continuous graph representing the difference 

 between the hurricane stage hydrograph and the water stage hydrograph that 

 would have prevailed at the same point and time if the hurricane had not 

 occurred. 



HURRICANE WIND PATTERN or ISOVEL PATTERN. An actual or graphical representa- 

 tion of near-surface wind velocities covering the entire area of a 

 hurricane at a particular instant. Isovels are lines connecting points of 

 simultaneous equal wind velocities, usually referenced 9 meters (30 feet) 

 above the surface, in meters per second, knots, or meters per hour; wind 

 directions at various points are indicated by arrows or deflection angles 

 on the isovel charts. Isovel charts are usually prepared at each hour 

 during a hurricane, but for each half hour during critical periods. 



HYDRAULICALLY EQUIVALENT GRAINS. Sedimentary particles that settle at the 

 same rate under the same conditions. 



HYDROGRAPHY. (1) A configuration of an underwater surface including its 

 relief, bottom materials, coastal structures, etc. (2) The description 

 and study of seas, lakes, rivers, and other waters. 



A-16 



