A Neotropical Savanna

The usual dry season winds here in Panama are caused by Northern Hemisphere air masses rushing toward the Intertropical Convergence Zone (ITCZ), or the Doldrums as we used to call this region. In January or so the ITCZ moves south away from its rainy season location near Panama. It takes its rain with it, and we’re left with dry air and winds.

This most recent (February 2009) wind episode was due to an unusual extension southward of the North American Jet Stream – it reached down to the eastern Caribbean, wreaking all sorts of havoc with the usual patterns in our area.

Here are images of the Jet Stream, starting at midnight Universal Time (midnight in Greenwich, England) on February 3 and continuing at 6-hour intervals.

By 1:00 PM Panama time (left-most of the next row of images), the trouble has begun in the Caribbean, but we haven’t yet seen it in Panama.

Here are the wind records from our weather station on February 3. Notice that the scale goes to 20 mph and that between 4 and 5 PM we had gusts approaching 15 mph. These are the wind velocities experienced by our weather station, of course, which is located in an open area but down-slope from the edge of our property. Since the wind was coming mostly from the north, and the mountain here slopes to the (roughly) south, it experiences some shelter from the wind blasts elsewhere on the mountainside. At any rate, low winds in the morning, high winds in the afternoon, and lower winds in the evening and night are the typical pattern for our dry season winds.

Here is the jet stream for February 4.

And our wind records for February 4. The winds started picking up during the night, really increased in the afternoon, and did not drop off at all in the evening or night.

It seems (to me) that the merging of the jet stream with that offshore crescent somehow shook up the normal weather patterns in the Gulf of Mexico and the Caribbean. During this time, I was seeing Caribbean Surface Analysis maps that showed gales off Costa Rica and Columbia. Unfortunately, I have not been able to locate an archive of these images, so I can’t match them up with the Jet Stream images. However, to continue with the comparison between the Jet Stream and our wind records:

Here is the Jet Stream for February 5.

And our wind records for February 5. Note the shift in scale on the y-axis. Maximum is now 30 mph rather than the 20 mph in the two previous records. There’s barely a respite from winds greater than 5 mph, which may not sound like much, but which causes the rustling of leaves and you definitely feel it.

Here are the Jet Stream images for February 6.

And our wind speed records for February 6. Note that the y-axis now goes up to 40 mph, and that between 12 noon and 1 pm we experienced a gust of over 30 mph. At 31 mph, you begin to see whole trees in motion.

The Jet Stream convergence with the crescent broke up completely on February 7.

The ripples from that event were still being felt in Panama, though. Note that the scale for February 7 goes to 35 mph, less than the day before, but still higher than for February 4.

By February 8 (today), the Jet Stream and the Atlantic crescent are completely separated.

Our wind speed scale now goes to 25 mph, and we have not yet returned to “normal,” if February 3 and 4 are any indication of normal wind behavior in our dry season, and I believe they are.

At this point, the Jet Stream does not look like it’s going to cause us continued trouble. I believe we’re now feeling the last ripples of the events that happened earlier. With any luck, that wind speed scale on our weather station report should drop back down to 20 mph maximum.

Incidentally, if you’d like to see these or other Jet Stream images animated, you can build your own animation loop by feeding in the date and times you’d like to watch.

Let’s hope that we’ll be back to our standard dry season winds tomorrow, with the air masses merely chasing the Doldrums.

UPDATE: 9 February 2009, 2:30 PM. So much for my predictions. The wind did not die down much last night.

Further, today the wind is back up strong enough that the y-axis scale is at a maximum of 30 mph.

For what it’s worth, here’s today’s forecast from Weather Underground:

Weather Underground Forecast for Monday, February 09, 2009. No tropical development is expected through the tropical Atlantic Ocean, but areas of showers and thunderstorms will remain. The strongest of these showers and thunderstorms will be along the coast of Central America from Honduras through Panama. Some of these thunderstorms may move inland into these countries.