Review of the year 2010
For comparison, see the 2009 archives.
The summary table of data we collected in 2010 supports our observations that we tend to have higher winds in the dry season and lesser winds in the rainy season. Not surprisingly, relative humidity and average solar input (an indication of cloud cover) will also be related to the monthly rainfall. We expect relatively little change in the temperatures although it ought to be somewhat cooler, on average, in the rainy season than it is in the dry season. This is the first year we have tracked average wind direction and maximum rain for one day. It is also the first year we've calculated the number of days that it rained during the month.
In October of this year we started collecting rain data from a manual rain gauge to compare with our WeatherHawk rain gauge. The WeatherHawk station consistently reads higher than the manual gauge by 25-30%. It has been shown that manual gauges tend to underestimate rainfall (1, 2) because of wind effects around the gauge itself. Because we are comparing our rainfall data with historical data obtained from manual gauges, we have added two "Adjusted" columns to our summary table. These columns, in red, show the WeatherHawk rainfall numbers reduced by 30%, for comparison with manual rain gauge data.
Rainy and dry seasons are clearly shown if you look at average monthly rainfall over time. The average is calculated from Señor Espinosa's rainfall data based on his records dating back to 1992. The dry season on this chart can be defined as those months during which we receive fewer than 10 inches of rain, that is, December through April. During the rainy season, May through November, we generally receive more than 10 inches of rain each month.
January through March
The early 2010 dry season, January through March was about what we would expect except that we had enough rainfall in February to keep the grass green. The red line on this chart is our 2010 data, contrasted with Espinosa's average rainfall.
In April our rainfall was hugely above average. We had 28.2 inches whereas the average for April is 6.7 inches. It rained during 15 of April's 30 days, but the heaviest precipitation came toward the end of the month. During the last six days in April, we were drenched with 24 inches of rain, receiving more than 5 inches during each of two of those days.
(Graphs of the amount of rainfall we received for each day of the month are presented on the Rain Days page.)
Rainfall in May was a return to average. In fact, it was nearly exactly average: we had 22.7 inches of rain; the average is 22.4 inches. We had 21 days of rain, but during only one of those days did it rain more than 5 inches.
In June of this year our rainfall was, like April, greatly above average. We had 42.8 inches; the average is 21.7 inches. It rained 27 of June's 30 days, and it rained more than 5 inches during one of those days. The temperature high dropped from May, as did the range. Not surprisingly, the average humidity increased and the solar input decreased from May.
In July we had more rainfall than in any month since Señor Espinosa began keeping records in 1992. We had 59.3 inches. July rainfall average is 17 inches; the previous July record was 38 inches.That record was broken at 4:06 PM on July 20, 2010.
The greatest rainfall for any month in the year was in September 1999 - at 55.3 inches. That record was broken at 4:29 PM on July 28, 2010.
It rained on 29 of July's 31 days, and it rained just over 5 inches on one of those days. All other factors that we track were about the same as they were in June.
The August rainfall broke as many records as did the rainfall in July. August rainfall average was until this year 25 inches; the record for August was 39.2 inches - that maximum rainfall record was exceeded on August 22 at 5:04 PM. In the end, we received 62.7 inches of rain in August, and during two of those days we received more than 7 inches of rain.
"Average" is an interesting idea and it occurs in our area only about 14% of the time. Perhaps this is because we are so often influenced either by El Niñno or La Niña events. The 2009 El Niñno was winding down during January through April, giving us erratic weather. During May El Niñno dissipated, and we reverted to average. The global system then was predicted to move to La Niña conditions during June through August. The August report from NOAA revised these expectations, and La Niña conditions were expected to strengthen and to continue through the Northern Hemisphere winter. Our high rainfalls - together with droughts in other places of the world - fall right into a strong La Niña pattern.
Rainfall records continued to be set in September, and we recorded 72 inches of rain for the month - that's 6 feet of rain! By now, though, we were becoming a little leery of the accuracy of our rain gauge. After the Palmira station reported heavy rainfall inaccuracies of more than 50% since June, we began to compare our readings against manual measurements. We have not yet found an actual rain gauge to buy so we have been using a 5-gallon bucket and a ruler to give us an estimate of rainfall. In August, the bucket showed lower readings than the station - on the order of 10-15%. In late September and now in October it is showing readings on the order of 25-30% lower than our station.
We will be checking our rain gauge with the help of Lloyd Cripe next week (it's a bit hard to get to). If we need to, we'll replace it. For now, to be conservative, we've simply done an arithmetical reduction of 30% for our rainfall since June. A graph of these reduced values against the average shows that we are experiencing extremely heavy rains even if our rain gauge is overestimating the numbers.
The average we use is based on data from Ricardo Espinosa. The rainest year in his records is 1999, when 209 inches fell during the year. It's interesting to compare our adjusted rainfall data with his records from 1999. That year in Potrerillos, June rainfall was well above average, but July was well below. Then August was above average again and rainfall peaked in September with 53 inches for the month. Our measured value in September was 72 inches and when we reduce that by 30%, we get 50 inches. Note, though, that our measured rainfall for both July and August, even when reduced by 30%, is far above average. And our total rainfall for this year will exceed that of 2009. Our recorded rainfall for the year as of the end of September was 298 inches. Reducing that by 30% gives 209 inches - exactly the same as Espinosa's 1999 record.
Of further interest is to compare Espinosa's 1999 data and our reduced 2010 data with the maximum data from Hidromet, the meterological service of Panama. We do not have individual year data from there, but we can show the maximum rainfall recorded during any year for each month. That is to say, we have the highest rainfall ever recorded for January, regardless of year, the highest for February, regardless of year, and so forth. Hidromet recorded 115 inches during one November! Because the scale has changed to accomodate that 115 inches, our 2010 reduced data and Espinosa's 1999 data are flattened out somewhat on the graph.
Well, our rain will either taper off, as it did in 1999, or it will increase, as it did in November of some year in the past.
To put these extraordinarily heavy rains in perspective, we updated our About Our Rain page to show how Potrerillos Arriba is one of the rainiest places in Panama.
The analyses of our data that we performed in September convinced us of the need to look critically at the WeatherHawk rainfall output. Lloyd Cripe came over and helped us calibrate it. The calibration showed that the station was working as it was supposed to. Then Norm Bader provided us with his spare manual rain gauge and we began keeping daily records to compare with the WeatherHawk. In the month of October, the WeatherHawk station consistently read between 25 and 30% higher than the manual gauge, with an average overestimate of 28.7%. As mentioned above, such differences might be expected due to wind effects around the manual gauge. It has also been shown that certain sheltered gauges may overestimate rainfall (2), but we do not know whether our WeatherHawk is overestimating. The true value for our rainfall may fall somewhere between the manual gauge readings and the WeatherHawk numbers. For the purposes of comparison with historical manual rain gauge data, we are continuing to do an arithmetical reduction (by 30%) of our rain data, since that is the difference we're finding between our WeatherHawk and a manual gauge.
Using these reduced numbers, an update of the graph showing 2010 rainfall data compared with the rainiest year (1999) in Espinosa's data and with the Hidromet data for Potrerillos Arriba is of interest.
It's encouraging that although the adjusted October rainfall (31 inches) is above average (28.7 inches), the trend from September to October is to move closer to average rather than to continue at the extreme values we have experienced since June. This Sep-Oct trend happened in 1999 as well.
The other observation of note is that, even using the adjusted numbers, our rainfall in 2010 has already surpassed the maximum rainfall seen in 1999, the previous year of maximum rainfall. Rainfall so far this year is 239 (adjusted) inches. In 1999, the total for the year was 231 inches. From the graph above, you can see that in 1999 Potrerillos did not experience the heavy rainfall in July and August that we experienced in 2010. It's been a nasty year in this respect.
I have referred to the La Niña phenomenon off and on while discussing our data this year. It's probably worth offering a brief review, since La Niña is not as well known as El Niñno. The NOAA definition is:
La Niña is characterized by unusually cold ocean temperatures in the Equatorial Pacific, compared to El Niñno, which is characterized by unusually warm ocean temperatures in the Equatorial Pacific. [Emphases mine.]
The effect is global. My rule of thumb of the effect of El Niñno on any particular region is that it brings weather opposite to that normally expected for the season. Thus, during an El Niñno, a summer season will be unusually cool. La Niña is the opposite of El Niñno. During a La Niña, the summer season will be unusually warm or hot. The NOAA page is worth reading for an explanation of how it comes about.
Of interest to us here in Panama is what conditions we might experience during a La Niña. This chart from NOAA, showing expected conditions from June through August, says it all:
Notice that Central America and Northern South America experience cool and wet conditions during these months (an exaggeration of our rainy season!). So, what about 1999? Was that a La Niña year as well?
Remembering that La Niñas are characterized by cold ocean temperatures in the Equatorial Pacific, let's look at a table of those temperatures for the years 1997 through 2001, from NOAA. The initials in the top row are for months of the year, e.g., DJF = December, January, February, etc.
You may remember that 1997-1998 was a severe El Niñno season, and that is shown in this chart as red numbers, indicating unusually warm ocean temperatures. That particular El Niñno season was followed by a much longer La Niña season (blue numbers) that lasted from mid-1998 through mid-2000. So, yes, Espinosa's 1999 record (until now) rainfall corresponds to a La Niña that lasted throughout 1999.
So what can we expect for the rest of this La Niña year? There is no map at the NOAA site for the months of September through November, but here's what we find for December through February.
Central America has nothing marked around it, suggesting that conditions during those months, even during La Niña years, may be about normal, or average. We can certainly hope that this will be the case as 2010 winds down.
We recorded 25 inches of rain in November. Our manual rain gauge continued to give readings lower than the WeatherHawk station, but for this month the difference between the two was 21%, rather than the 29% difference we saw in October. Nevertheless, for consistency, to compare our data with historical rain data taken with a manual gauge, we'll continue to adjust our numbers by 30%. So the table at the top of this page shows that we will use 18 inches as our comparison number for November.
The monthly average for November is 15 inches and the historical maximum is 21 inches. So, although rainfall in November was above average, we're no longer setting rainfall records. During the period of June through October, our weather station recorded an average of 56 inches per month - that's 39 inches when we reduce the number. So it's safe to say that we experienced more than three feet of rain during those months, and if our station is more accurate than manual gauges, then we experienced well over four feet of rain each month. That there was only about 1.5-2 feet of rain in November was a great relief.
The lesser amount of rain shows up in both the number of days we had rain - 25 days in November vs. 26 - 29 days in previous months - and in the maximum amount of rain we received for one day: 2.8 inches in November vs. 3.6 - 5.2 inches in previous months). We did have a lot of fog and overcast days, and our solar input was actually down a bit from October - 95 watts per sq. cm in November vs 99 in October.
On December 3, the Panamanian newspaper La Prensa reported that the meterological service announced that sporadic rains will continue throughout the upcoming dry season. Usually in Potrerillos, the driest two months of the dry season, January and February, have fewer than two inches of rain. The months that bracket the driest months, December and March, usually have fewer than five inches of rain. Just to give you a heads-up, we've already had more than five inches of rain in December - on the second day of the month, we had 5.87 inches in our rain gauge. This rain came when a system that had the potential to turn into a tropical storm was sitting off the coast. But that's a story for next month.
On November 30, Lloyd Cripe of Boquete Weather presented a talk, "Rain, Rain Go Away," on our climate in Panama. The slides tell the story well, even without the words he spoke. It must have been an enjoyable presentation for all present.
We recorded 9 inches of rain in December. Our manual rain gauge continued to give readings lower than the WeatherHawk station, but for this month the difference between the two was 10%, rather than the 29% difference we saw earlier in the year. Nevertheless, for consistency, to compare our data with historical rain data taken with a manual gauge, we'll continue to adjust our numbers by 30%. The table at the top of this page shows that we will use 7 inches as our comparison number for December.
The monthly average for December is 4.6 inches and the historical maximum is 14.8 inches. So, although rainfall in December was above average, it is approaching average. Most of the rain this month fell early on - of the 9 inches the WeatherHawk station recorded for the month, 6.9 of those inches were on December 1 (see the graph on the Rain Days page). This heavy rain was due to a system that sat off the coast of Panama and Costa Rica. At the time, the Graphical Tropical Weather Outlook from NOAA showed what it called an "incipient tropical storm" in the area.
Later the storm, in a summarized graphic, made the NASA Earth Observatory Image of the Day.
Later in the week and well into December, severe weather occurred in Eastern Panama, weather that we in Western Panama were lucky to avoid. NOAA reported in its State of the Climate for December 2010:
Heavy rainfall and flooding in Panama killed 10 people and damaged over 2,500 homes. The downpours forced the Panama Canal to close on December 8th and 9th, the first time the canal closed due to weather conditions since its opening in 1914. The rainy season was particularly severe this year.
By December 11, the damage caused a collapse of the Centennial Bridge, which is (was) the newest and largest bridge over the canal. Quoting from a report on The Weather Network:
"The roadway's security has definitely been compromised here," said Federico Jose Suarez, Panama's Minister of Public Works. "The reason is that the filler dirt is saturated by the rain and collapsed (the bridge). It was moving laterally until it moved that part of the roadway and it keeps moving. It can not be controlled."
So we in Chiriqui have been comparatively lucky. When we compare our December rainfall with the average of Espinosa's data and with the 1999 La Niña year, we see that December is near average both for this year and for 1999.
Wrap-up: We have come to the end of a very wet 2010. By all accounts, the unusual amounts of rain were due to a La Niña event. Our WeatherHawk station recorded 377 inches for the year. This number may be high, but when we reduce it by 30% to make it comparable to manual rain gauge data, we still have 264 inches (22 feet!), which exceeds Espinosa's record of 231 inches by 2 feet, 8 inches. In the La Prensa article cited above, the National Civil Protection System (Sinaproc) pronounced 2010 the "wettest year." Our records from Potrerillos agree.