April 2009 Weather Report for Potrerillos Arriba
April is the last month of the dry season in our area, and it was a very, very dry month this year. Normally, based on the 16-years’ worth of rainfall data collected by Ricardo Espinosa (see the About Our Rain page), Potrerillos Arriba receives fewer than 5 inches of rain in March and more than 5 inches of rain in April.
This year the pattern was reversed. We received more rain in March (7.4 inches - all of it in the last two days of the month) than in April (0.9 inches). A really dry April is not unprecedented, however. Espinosa’s records show how April rainfall varies greatly around a 7-inch average.
The years 2001, 2002, and 2004 were just as dry as this year, and 2005 had only 2.6 inches for the month. Annually, two of the three dry April years were somewhat drier than average. The average annual rainfall for these data is 176 inches. The years 2001 and 2002 had less rainfall than average (162 and 122 inches, respectively), but 2004 (at 178 inches) was slightly above the average.
It seems fair to say that a low rainfall April does not necessarily predict a low rainfall year. When we plot April rainfall vs annual rainfall, there is a trend, but the relationship is not significant (the R squared value needs to be greater than 0.9 to show significance - our value for 16 years’ worth of data is only 0.1).
Temperature
Temperature ranges and averages have been fairly steady from February, the first full month for which we have data, through April. Average temperature was 74o F for all three months, and the low was 59-60o F. Maximum temperature showed the greatest variation, with 95o F being the high in March and 90o F being the high in April.
The feel of the temperature, though, was a bit different from what you’d think looking at these numbers. April felt hotter than March, as it has done in the years we’ve been here. The reason for this is the drop in winds in April - there’s little in the way of a cooling breeze, on average.
Further, the relative humidity increased in April. The combination of less wind and higher humidity made April seem like our hottest month this year.
The increase in relative humidity was related to the increase in cloud cover in April. Cloud cover increases in Panama from January through at least June because as the track of the sun moves northward across the earth, the Intertropical Convergence Zone in the ocean - the region of the Doldrums - moves toward Panama and brings, if not rain, then plenty of clouds. Cloud cover cuts down on sunlight, and so the measure of solar input decreased from 207 watts/cm2 in February to 184 watts/cm2 in April.
Summary
The following table summarizes the data we’ve gathered since the beginning of February.
Temperature variation is small for the three months, but the average wind speed drops in April and the relative humidity increases, making April feel like a hot month. Rainfall was well below normal for the month, but we’re hoping this does not predict a drier than normal rainy season to come.