September 2009 Weather Report for Potrerillos Arriba

We had only 14.8 inches of rainfall in September - the most interesting data for the month.

The average rainfall in our area for the month of September, based on Sr. Ricardo Espinosa's data from 1992-2008, is 32.1 inches. The driest September in that period of time was 16.0 inches in 1992, which was an El Niño year. September 1992 was even drier than September 1997 (20.1 inches) although the 1997-1998 El Niño is considered to be the strongest such event ever recorded.

The Espinosa data comes from a station a little farther up the mountain: elevation at Espinosas = 880 m; elevation at our station = 750 m. We need to ask whether it is legitimate to compare our data with theirs. In the graphs that follow, our station data is called "Finca Trogon" after the name of our property. The first graph plots the Finca Trogon data against the Espinosa data so we could test the correlation between the two. A stastical test on the data shows that the correlation has a 90% chance of being true.

This means that if we have a high rainfall for the month, it is extremely likely that the Espinosas will have a high rainfall as well, and vice versa.

The second graph shows that the two stations are tracking pretty closely this year. Further, the Espinosa station showed only 10.5 inches rainfall this September. This a record low for September at their station.

The rainfall is therefore alarmingly low for the month.

In early September, the National Weather Service Climate Prediction Center/NCEP/NWS issued an El Niño Advisory, stating that the current "El Niño is expected to strengthen and last through the Northern Hemisphere winter 2009-2010." Their most recent weekly report confirms the prediction.

Having suffered the effects of the 1997-1998 El Niño event, Panamanians are keenly aware of the potential dangers of this year's event. Since much of Panama's electricity comes from hydroelectric sources, the possibility of power outages is real. (Panama's neighbor Costa Rica is in fact predicting electricity cuts and droughts on the Caribbean slopes of the country.) Also, Joyce read in La Prensa, the paper edition, that the rice growers are not doing their second seeding of rice this year because of the expected dry conditions due to El Niño. Unfortunately, I cannot find an online version of the story to provide a link, and we no longer have a copy of the issue. A discussion with any Panamanian in our area will ultimately come around to observations about this season's dry weather and about El Niño, which has been covered in a number of television news reports.

Long-time Panama resident Carla Black has written to me that the El Niño pattern for Panama "...usually is dry, dry, dry. [The] real dry season will probably start earlier - in November - and extend up to a month later. I don't expect a drop of rain in between."

Other results

The average temperature for September was 72.1 F, about the same as it has been since May. Likewise the monthly low of 63.1 F is about the same as for those months. Monthly high was 88.5, somewhat lower than May's 90.9 but about the same as June - August.

Average wind speeds (1.8 mph) likewise were about the same as they have been since May, but the maximum wind speeds from July through September have been a bit higher than one would expect for this time of year.

The average solar input at 125 watts/cm2, the highest since April, indicates that we had less cloud cover in September than in May through August, and underscores the low rainfall number.

Summary