What is
the heat index?
During an average day, your body burns about 2,000
calories (when you are exercising heavily, it burns a lot more).
That means that during waking hours, you are burning about 2
calories a minute. These 2 calories have the ability to raise
the temperature of 1 kilogram of water 2 degrees C. If you weigh
50 kilograms (110 pounds), your body temperature rises one-twenty-fifth
of a degree C (one-twelfth of a degree F) every minute.
Your body needs a way to dump that excess heat.
If it doesn't, then body temperature rises into the danger zone
in a matter of 30 minutes. Up to about 80 degrees F (24 degrees
C), it's easy to dump excess heat simply through radiation (this
is why air temperature "feels" comfortable at up to about 80
degrees F).
Above 80 degrees F, your body does not have enough
surface area to get rid of the heat fast enough, so your body
turns on your sweat glands to make evaporative cooling possible.
Evaporative cooling works great if the air is
dry. In high humidity, however, it doesn't work very well --
the sweat cannot evaporate because the air is already saturated
with humidity.
In high temperature/high humidity environments,
your body can get into a dangerous situation where it cannot
radiate or evaporate the heat away. The heat index that you
see on the evening news is designed to make you aware of these
dangerous situations. The heat index takes the day's temperature
and humidity into account and calculates what the temperature
would be if the air were at 25-percent humidity or so (very
dry). On this scale, high humidity can make you excruciatingly
hot because your body has no way to eliminate excess heat. For
example, 100 degrees F with 100-percent humidity is the equivalent
of 195 degrees F at 25-percent humidity -- nearly the boiling
point of water!
San Felipe is quite humid and hot during the summer
months. That is why many people leave at that time of year.
If you plan to visit during the summer, please remember that
your body is going to feel more uncomfortable and fatigued because
of the heat index. The charts below will give you a good idea
of what your body feels, despite what you acknowledge from the
thermometer hanging on the wall.
HEAT
INDEX °F (°C) |
|
RELATIVE
HUMIDITY (%) |
Temp. |
40 |
45 |
50 |
55 |
60 |
65 |
70 |
75 |
80 |
85 |
90 |
95 |
100 |
110
(47) |
136
(58) |
|
|
|
|
|
|
|
|
|
|
|
|
108
(43) |
130
(54) |
137
(58) |
|
|
|
|
|
|
|
|
|
|
|
106
(41) |
124
(51) |
130
(54) |
137
(58) |
|
|
|
|
|
|
|
|
|
|
104
(40) |
119
(48) |
124
(51) |
131
(55) |
137
(58) |
|
|
|
|
|
|
|
|
|
102
(39) |
114
(46) |
119
(48) |
124
(51) |
130
(54) |
137
(58) |
|
|
|
|
|
|
|
|
100
(38) |
109
(43) |
114
(46) |
118
(48) |
124
(51) |
129
(54) |
136
(58) |
|
|
|
|
|
|
|
98
(37) |
105
(41) |
109
(43) |
113
(45) |
117
(47) |
123
(51) |
128
(53) |
134
(57) |
|
|
|
|
|
|
96
(36) |
101
(38) |
104
(40) |
108
(42) |
112
(44) |
116
(47) |
121
(49) |
126
(52) |
132
(56) |
|
|
|
|
|
94
(34) |
97
(36) |
100
(38) |
103
(39) |
106
(41) |
110
(43) |
114
(46) |
119
(48) |
124
(51) |
129
(54) |
135
(57) |
|
|
|
92
(33) |
94
(34) |
96
(36) |
99
(37) |
101
(38) |
105
(41) |
108
(42) |
112
(44) |
116
(47) |
121
(49) |
126
(52) |
131
(55) |
|
|
90
(32) |
91
(33) |
93
(34) |
95
(35) |
97
(36) |
100
(38) |
103
(39) |
106
(41) |
109
(43) |
113
(45) |
117
(47) |
122
(50) |
127
(53) |
132
(56) |
88
(31) |
88
(31) |
89
(32) |
91
(33) |
93
(34) |
95
(35) |
98
(37) |
100
(38) |
103
(39) |
106
(41) |
110
(43) |
113
(45) |
117
(47) |
121
(49) |
86
(30) |
85
(29) |
87
(31) |
88
(31) |
89
(32) |
91
(33) |
93
(34) |
95
(35) |
97
(36) |
100
(38) |
102
(39) |
105
(41) |
108
(42) |
112
(44) |
84
(29) |
83
(28) |
84
(29) |
85
(29) |
86
(30) |
88
(31) |
89
(32) |
90
(32) |
92
(33) |
94
(34) |
96
(36) |
98
(37) |
100
(38) |
103
(39) |
82
(28) |
81
(27) |
82
(28) |
83
(28) |
84
(29) |
84
(29) |
85
(29) |
86
(30) |
88
(31) |
89
(32) |
90
(32) |
91
(33) |
93
(34) |
95
(35) |
80
(27) |
80
(27) |
80
(27) |
81
(27) |
81
(27) |
82
(28) |
82
(28) |
83
(28) |
84
(29) |
84
(29) |
85
(29) |
86
(30) |
86
(30) |
87
(31) |
|
Category |
Heat Index |
Possible heat disorders
for people in high risk groups |
Extreme
Danger |
130°F or higher
(54°C or higher) |
Heat stroke or sunstroke
likely. |
Danger |
105 - 129°F
(41 - 54°C) |
Sunstroke, muscle cramps,
and/or heat exhaustion likely. Heatstroke possible
with prolonged exposure and/or physical activity. |
Extreme
Caution |
90 - 105°F
(32 - 41°C) |
Sunstroke, muscle cramps,
and/or heat exhaustion possible with prolonged exposure
and/or physical activity. |
Caution |
80 - 90°F
(27 - 32°C) |
Fatigue possible with
prolonged exposure and/or physical activity. |
|
Here's
a link to a heat index caculator (bottom of page).