The area around Potrerillos is one of the rain "hot spots" in Panama. This image of western Panama, taken from the Gerencia de Hidrometerología (meterologial service of Panama) map section, shows the rainiest places in dark blue. The Potrerillos hot spot is the western blue region just above the 950,000 grid line.
Data from the Gerencia de Hidrometerología ("hidromet" for short) for Potrerillos and nearby Bajo Boquete shows that on the average, Potrerillos receives about 20 inches of rain more than Bajo Boquete each year. But the maximum rainfall for any given month in each area differs greatly: on average, Potrerillos has received 76 inches more than Bajo Boquete in months of maximum rainfall.
We are fortunate enough to have access to Ricardo Espinosa's daily rainfall data from April 1992 through the present. The correlation between his averages and those of hidromet, which goes back to 1955, is 98% - so we feel great confidence in his numbers. His monthly average is more than 6 inches higher than hidromet's, but his maximum month is 59 inches lower than hidromet's maximum. Because the correlation is so strong between the two stations, we believe these monthly variances simply reflect microclimate differences within in the Potrerillos area.
Average monthly rainfall looks like this - peak month is September while January and February are the driest months. The pattern is virtually identical for hidromet (blue) and for Espinosa (green).
The next table is the annual breakdown for monthly averages of Espinosa's data. We'll add data as we obtain it.
This chart, based on the table above, of annual rainfall for the 12-year period shows 1997 and 2002 as the driest years (these were El Niño years) and 1995, 1998, 1999, 2003, 2007, and 2008 as the wettest years, with more than 200 inches rainfall for each of those years. Data were not collected earlier than April of 1992, and we have yet to obtain the December 2009 data, so those years are expected to have low totals. The red horizontal line shows the average rainfall (nearly 183 inches) for the years 1993-2008.