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1993 ) . Humid conditions , which add to the discomfort of high temperatures , o N.cur when an area of high atmospheric pressure traps hazy , damp air near the ground . Human bodies dissipate heat in one of three ways : by varying the rate and depth of blood circulation ; by losing water through the skin and sweat glands ; and by panting . As the blood is heated to above 98 . 60 , the heart begins to pump more blood , blood vessels dilate to accommodate the increased flow , and the bundles of tiny capillaries penetrating through the upper layers of skin are put into operation . The body' s blood is circulated closer to the surface , and excess heat is released into the cooler atmosphere . At the same time , water diffuses through the skin as perspiration . The skin handles about 90 % of the body's heat dissipating function . Heat disorders generally have to do with a reduction or collapse of the body' s ability to cool itself by circulatory changes and sweating , or a chemical (salt) imbalance caused by too much sweating . When the body cannot cool itself, or when it cannot compensate for fluids and salt lost through perspiration , the temperature of the body's inner core begins to rise and heat- related illness may develop . Studies indicate that, other things being equal , the severity of heat disorders tend to increase with age . Heat cramps in a 17-year old may be heat exhaustion in a 40-year old , and heat stroke in a person over 60 . When the temperature gets extremely high , the NWS has increased its efforts to alert the general public as well as the appropriate authorities by issuing speci I weather statements . Residents should heed these warnings to prevent heat- related medical complications . As a result of the latest research findings , the NWS has devised the " Heat Index" ( HI ) . The HI , given in degrees Fahrenheit, is an accurate measure of t ow hot it really feels when relative humidity is added to the actual air temperature . The NW will initiate alert procedures when the HI is expected to exceed 105 ° F for at least two cor secutive days . Possible heat disorders related to the corresponding HI are listed below . • Heat Index of 130 ° F or higher — Heatstroke/sunstroke with exposure for people in higher risk groups ; • Heat Index of 105 ° F- 130 ° F — Sunstroke , heat cramps , and heat exhaustion likely and heatstroke possible with prolonged physical activity; • Heat Index of 90 ° F- 105 ° F — Sunstroke , heat cramps with prolonged exposure ; and • Heat Index of 80 ° F-90 ° F — Fatigue possible with prolonged exposure and physical activity ( NWS , 1999b ) . Historic Events. The highest temperature ever recorded in the state was on 29 June 1931 at 103 ° F in Monticello at an elevation of 207 feet ( NCDC , 1999 :) ) . In a normal year, approximately 175 Americans die from extreme heat . However, in 199 .5 , the death toll was 1 , 021 ( NWS , 1997 ) . There were no data available to document previous occurrences of extreme heat by jurisdiction . Because temperature extremes are hazards that are not bounded by geographic or topographic characteristics , there are no definite means to determine whetrier or not the extent of this hazard differs from jurisdiction to jurisdiction within Indian River County . *400 4-42