La Message Board Archives

Re: heat, nearby weather stations 101

Posted by Bret B on July 11, 2014, 10:09 am, in reply to "heat"

Yesterday's afternoon maximum temperature was 95.4F / 35.2C here at my place (see my caveats below.) Combined with the afternoon minimum relative humidity of 58%, the maximum Heat Index was 113F / 45C. (This assumes that the max temp happened at the same time as the min RH. That's usually true but not always.)

It's now been 8 days since the last rain, and the heat has been creeping up steadily since then. Luckily it's not quite as bad as it got up to on June 18th before that 2 weeks of nice rains. June 18th the max temp hit 96.4F / 35.8C, with an RH of 60%, for a HI of 117F / 47C.

I don't see any notable sources of rain coming our way anytime soon. There are the usual late afternoon thunderstorm build-ups over the mountains, but those don't usually make it to the coast. We'll just have to tough it out for a while longer!

By the way, the only "official" government weather stations around here are at the Manzanillo airport, and in downtown Manzanillo. I believe any weather sites that show conditions in Barra are just using the airport numbers. Sometimes it's not easy to dig behind the numbers to discover where they came from. The Weather Underground site can be set to include data from personal weather stations. The closest one of those has been in Santiago (suburb of Manzanillo,) but this one has been offline for several days now. When it's online, it's the most complete and reliable weather station anywhere near us, government or not.

A couple cautions about the Manzanillo airport weather data:

1. the station doesn't report data when the airport is closed (at night.) This means the data for temp, RH, winds, pressure, etc may be invalid if you look at any weather page at night. They usually just show you the most recent data, even if it might be several hours old. And this also means that any average historical statistics are useless since they won't include any nighttime data.

2. The airport doesn't seem to have a working rain gauge. I haven't seen rain data reported by them for a few years now. But most weather sites don't know this; they just report 0.0" of rain all the time. So historical rain stats are also invalid.

Now for the caveats about my weather data:
* My basic wireless weather station measures temperature and humidity, and I record the daily max and min of both numbers. I do have occasional gaps in the data record when I go out of town (a few weeks per year.)
* The outdoor sensor is located in the shade on my back porch, half a block south of the Jardin, and a block or two from the ocean.
* My back yard is partially surrounded by 2-story apartments, so I don't get much of the sea breeze here.
* If you are on the beach or up on the hill with a nice breeze, you would probably have afternoon max temps somewhat lower than mine. How much? I would guess maybe 2-4F / 1-2C lower, but I haven't done any correlation experiments.
* My wireless rain gauge is located out in the middle of the back yard away from trees and tall walls.
* It has a convenient memory so when I get back from a trip I can read out the daily rainfall data for the last 7 days, and the weekly data for the last 7 weeks.
* I do have a black thumb with rain gauges, though. I've had 3 or 4 fail on me. Then I have some gaps in the rain data until I can get a replacement. If I'm in town I just switch to a jelly jar and ruler. If it fails while I'm out of town I gather whatever rain data I can from others (like Daniel's famous shot glass,) or other gauges people have here in town.
* So between Deanna's data from 2004 to 2011, and mine since then, we have a pretty decent 10-year data set. Including nighttime data !


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