Climate Narrative for the Caribbean National Forest, Puerto Rico.
Prepared by the Natural Resources Conservation Service National Water and Climate Center, Portland,
Oregon.
Climate Tables are created from climate station Juncos 1 NNE, Puerto Rico. Much of the additional
information used to write this narrative was obtained from the new mean monthly and annual
precipitation and temperature maps created by the Spatial Climate Analysis Service at Oregon State
University, utilizing their PRISM spatial distribution modeling system.
Thunderstorm days, relative humidity, percent sunshine, and wind information are estimated from First
Order station San Juan, Puerto Rico.
Table 1 gives data on temperature and precipitation for the survey area as recorded at Juncos in the
period 1961 to 1990. Table 2 shows probable dates of the first freeze in fall and the last freeze in
spring. Table 3 provides data on the length of the growing season.
In winter, the average temperature is 73.2 degrees F and the average daily minimum temperature is 62.4
degrees. The lowest temperature on record, which occurred at Juncos on April 11, 1981, was 50 degrees.
In summer, the average temperature is 79.2 degrees and the average daily maximum temperature is 88.6
degrees. The highest temperature, which occurred at Juncos on July 16, 1954, was 100 degrees.
PRISM maps of Puerto Rico indicate that over the national forest area temperatures are highly
correlated with elevation. In January average high temperatures are between 70 and 80 degrees, and
average low temperatures are between 57 and 64 degrees. In July, average high temperatures are between
75 and 85 degrees, and average low temperatures are between 64 and 72 degrees.
Growing degree days are shown in Table 1. They are equivalent to "heat units". During the month,
growing degree days accumulate by the amount that the average temperature each day exceeds a base
temperature (shown here for 50 degrees F).
The average annual precipitation is 66.47 inches. However, most, if not all of the Caribbean National
Forest area lies in a much wetter precipitation area, being on the northeast corner of Puerto Rico, and
at elevations up to nearly 1100 meters. Precipitation maps indicate most of the national forest area
receives between 120 and 160 inches of precipitation per year, with the lowest elevations receiving
between 80 and 120 inches. The heaviest 1-day rainfall during the period of record was 14.40 inches at
Juncos on December 8, 1987. Thunderstorms occur on about 40 to 50 days each year, and most occur
between May and October, with the highest frequency in September. This also is the most likely time of
year for tropical storms, with the full season going from June to early December.
The average relative humidity in mid-afternoon is generally about 65 percent at lower elevations, and
near 70 to 75 percent at higher elevations. Humidity is higher at night, and the average at dawn is
about 80 to 85 percent at lowest elevations, and around 90 percent a higher elevations. The sun shines
approximately 65 percent of the time for the year as a whole, ranging from near 60 percent in November
and December to nearly 75 percent in March. The prevailing wind is from the east-northeast. Average
wind speed is highest, around 10 miles per hour, in March and April.
TABLE 1.--TEMPERATURE AND PRECIPITATION
(Recorded in the period 1961-90 at JUNCOS 1 NNE, PR5064)
|
|
|
Temperature
|
Precipitation
|
|
_
|
|
|
|
2 years in
|
|
|2 years in 10|
|
Month
|
|
|
|
10 will have-| Average |
| will have-- | Average |Average
|Average|Average|Average| Maximum | Minimum |number of|Average|
|
|number of|snowfall
| daily | daily |
|temperature|temperature| growing |
| Less | More |days with|
|maximum|minimum|
| higher
| lower
| degree |
|than--|than--|0.10 inch|
|
|
|
| than-| than-| days*
|
|
|
| or more |
|
|
|
|
|
|
|
|
|
|
|
| 0F
| 0F
| 0F
|
0F
|
0F
| Units | In
| In | In |
|
In
|
|
|
|
|
|
|
|
|
|
|
January-----| 83.5 | 61.8 | 72.7 |
88
|
54
|
697 | 2.67 | 1.63| 3.59|
7
|
0.0
|
|
|
|
|
|
|
|
|
|
|
February----| 83.9 | 61.5 | 72.7 |
89
|
54
|
637 | 2.36 | 1.24| 3.33|
6
|
0.0
|
|
|
|
|
|
|
|
|
|
|
March-------| 85.0 | 62.5 | 73.8 |
90
|
53
|
724 | 2.97 | 1.42| 4.30|
6
|
0.0
|
|
|
|
|
|
|
|
|
|
|
April-------| 86.1 | 64.5 | 75.3 |
91
|
56
|
758 | 3.71 | 1.82| 5.35|
6
|
0.0
|
|
|
|
|
|
|
|
|
|
|
May---------| 87.1 | 67.8 | 77.4 |
92
|
59
|
850 | 7.53 | 3.40| 11.08|
11
|
0.0
|
|
|
|
|
|
|
|
|
|
|
June--------| 88.2 | 69.7 | 78.9 |
92
|
63
|
854 | 5.49 | 2.04| 8.36|
11
|
0.0
|
|
|
|
|
|
|
|
|
|
|
July--------| 88.7 | 70.1 | 79.4 |
93
|
64
|
901 | 5.91 | 3.68| 7.91|
10
|
0.0
|
|
|
|
|
|
|
|
|
|
|
August------| 88.8 | 69.6 | 79.2 |
94
|
63
|
900 | 7.98 | 5.20| 10.50|
12
|
0.0
|
|
|
|
|
|
|
|
|
|
|
September---| 88.9 | 68.9 | 78.9 |
93
|
62
|
867 | 7.18 | 3.64| 10.26|
11
|
0.0
|
|
|
|
|
|
|
|
|
|
|
October-----| 88.3 | 68.5 | 78.4 |
93
|
63
|
865 | 8.33 | 4.44| 11.74|
12
|
0.0
|
|
|
|
|
|
|
|
|
|
|
November----| 86.6 | 66.6 | 76.6 |
92
|
59
|
790 | 6.97 | 2.77| 10.51|
10
|
0.0
|
|
|
|
|
|
|
|
|
|
|
December----| 84.3 | 63.8 | 74.1 |
90
|
55
|
733 | 5.40 | 2.29| 8.04|
10
|
0.0
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Yearly:
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Average---| 86.6 | 66.3 | 76.4 |
--|
--|
--- |
--- |
---|
---|
--|
--|
|
|
|
|
|
|
|
|
|
|
Extreme---|
96 |
50 |
--- |
95
|
52
|
--- |
--- |
---|
---|
--|
--|
|
|
|
|
|
|
|
|
|
|
Total-----|
--- |
--- |
--- |
--|
--|
9577 | 66.47 | 41.50| 78.54|
112
|
0.0
|
|
|
|
|
|
|
|
|
|
|
* A growing degree day is a unit of heat available for plant growth. It can be calculated by adding the maximum
and minumum daily temperatures, dividing the sum by 2, and subtracting the temperature below which growth is minimal
for the principal crops in the area (50 degrees. F)