How's the Weather?

It has been 3 full weeks since we left port in Manta, and tonight we are heading to our southern-most point on the trip (until Tahiti).



The red line shows our progress as of Friday afternoon.

During our deck work and free time, many of us have been enjoying abundant sunshine along with scattered showers each day this week. Some of the crew who are familiar with the weather at this latitude tell us we can expect both rain and sunshine every day for the rest of our trip. The rain isn’t warm, and it’s more like a mist than a downpour. Not pleasant, but not unpleasant.

The further offshore we sail, the warmer the weather will become. We can predict this based on satellite imagery of sea surface temperature like the one shown below.

Sea surface temperature

The sun heats the seawater as well as our air, making the two the same temperature within 1°C. They stay at this temperature both day and night, which is great because I’m often in shorts during our middle of the night casts. The high humidity (75 - 85%) is one of the reasons that the air temperature stays warm after sunset. Another is the huge, warm body of water we’re floating on.

Why does the water help to keep the temperature constant?

You may remember your high school Chemistry teacher talking about “heat capacity”. This is a chemical property of matter, and describes how well (or not well) a molecule is able to retain its heat (a form of energy). Compared to (dry) air, my bedding, a piece of paper – you name it – water is much better at holding its heat in. Don’t believe me? An easy way to prove this to yourself is to put one pan of water and a second pan with a few layers of aluminum foil on its bottom in your oven at 325°F; wait for ~15 minutes until they’re both hot, and then pull them out. After a minute, you should be able to pick up the foil with bare hands; the water (and its pan) will both still be piping hot! This is because the foil has a low heat capacity (readily losing its warmth) while the water with its high heat capacity stays hot (and also keeps its pan hot).

Flash back to our South Pacific Ocean with its thousands of miles of warm surface water and humid air; the sun sets but there are millions of gallons of water which release their heat very slowly. So slowly the sun is up again before the sea and air temperature can drop! [Bonus points to those of you who remember that temperature is actually a measure of energy – related to how fast atoms/molecules vibrate.]

But what if the satellite image looks different next week? 

Offshore, the image above is unlikely to change much. This is because the major water currents are driven by winds. Near the equator, you can see a band of cooler (green) waters stretching from South America towards the west. This is because the prevailing winds near the equator blow from east to west, and push colder water off towards Asia. Near 15°N and 15°S, the winds blow in the opposite direction of the equatorial wind and bands of warmer (yellow/orange) water can be seen that originated in the west. Because these wind patterns are ~constant year-round, we can be confident our satellite image won’t change much while we’re out here.

For those of you still with me through this wordy post… 
At night, we’ve had clear skies and seen a bunch of starts – including my favorite constellation Orion the Hunter – and a planet (Jupiter maybe?)

The moon (and clouds) reflecting on the ocean.