December 2009 Weather Report for Potrerillos Arriba

December continues the winding down of the rainy season, a winding down that began in November as is clear from the blue line in the chart below. The blue line on the chart represents a 16-year average of rainfall data from this area. The red line shows the rainfall for 2009 as recorded by our weather station. There was an unusually high rainfall for April and an unusually low rainfall for September, normally the rainiest month of the year. We had 9.1 inches of rainfall this December, about double the average of 4.6 inches.

Our average annual rainfall is 175 inches. This year we had 172.5 inches, just short of average. A glance at the above chart shows that the months with greater than average rainfall just about balanced the months with less than average rainfall, including the severely dry month of September.

The National Weather Service Climate Prediction Center/NCEP/NWS issues a monthly El Niño Advisory. The most recent advisory is predicting that the current El Niño will last into the Northern Hemisphere spring (April-May-June). The 2009-2010 El Niño strengthened in December, but we in Potrerillos did not experience an El Niño impact. If we had, our rainfall would have been lower than average. Instead, it was well above average.

So far, it seems that the only impact we have experienced from the 2009-2010 El Niño was in September 2009, when our precipitation was just about half what it is on average. As discussed in November, a quick analysis of rainfall in Potrerillos during other El Niño years suggests that El Niño droughts tend to last for several months. This year is unusual in having its drought (so far) restricted to September. The extra rainfall back in May, incidentally, coincided with the end of the 2009 La Niña.

Other results

The average temperature for December was 72.3 F, a little warmer than it was in October and November. However, the monthly low of 60.3 F is the coolest low since April. The monthly high was 90.1. This is a 30-degree temperature range. Not a big deal for the temperate latitudes, especially in continental interiors, but our temperature ranges are usually not very great. The pattern we're seeing in 2009 is that temperature ranges are less than 30 degrees in the rainy season (May-October) and greater than 30 degrees heading into and during the dry season. When you think about it, this makes sense. There's more sun to heat up the air during the dry season, and more overcast skies to soften the sun's heat during the rainy season.

Average wind speeds (2.1 mph) began to increase in December and we experienced some fine wind gusts, the highest one being 24 mph.

The average solar input at 126 watts/cm2, was an increase from November and corresponds to the increased sun, lower rainfall for the month.

2009 Data

Recently, La Gringa, a blogger from La Ceiba, Honduras, posted her first year's worth of rainfall data. Here's the comparison of what she found for La Ceiba and what we found for Potrerillos.

Although both countries are in Central America, the dry seasons barely overlap. The dry season lasts from March to June in La Ceiba whereas it lasts from January to March in Potrerillos. As you can see from the graph at the top of the page, April 2009 was an anomaly in Potrerillos, and is normally considered the first month of the rainy season there. The rainy season lasts from July-August to February in La Ceiba whereas it normally lasts from April to November-December in Potrerillos. Both Honduras and Panama have serious rain (more than 10 inches) in October and November. In average years that stretch of time with more than 10 inches per month lasts from May through November in Potrerillos (see top graph), and may last from August through November in La Ceiba. La Gringa will know more after further collection of data.

Another way to look at it is to note that La Ceiba had more rain than Potrerillos in the months of November-April (March was close enough to ignore), and less rain than Potrerillos in the months of May-October. Potrerillos had about 44 more inches of rain than La Ceiba did in 2009. There was, interestingly, low rainfall in both La Ceiba and Potrerillos in September, suggesting that the El Niño effect in that month influenced much of Central America (if one can say that from two data points!).

Summary