18Z Models Running

[MWatkins]

System is starting to slow down a little...although this is just a best guess at a center of circulation. The 18Z tracks were initialized at:

13.5 North
65.0 West
Movement: 290 at 19 knots
Winds : 30 knots

More when the models finish...

MW

[MWatkins]

Actually...they finished 30 mins ago...dooh:

http://www.srh.noaa.gov/data/WBC/CHGHUR.0407201822

MW

[chadtm80]

lol.. Thanks Mike

[Weatherboy1]

I can't seem to make up my mind about whether this thing is dying off (deep convection really fading, earlier outflow boundary flying W) or improving in organization (more evidence in visible satellite imagery of significant spin right around the 14-15N 66W area). Arghhh. These tropical waves sure are annoying ... much harder to figure out what's going on than when you have a nice eye to track and reconnaissance reports of 120 mph winds!

[Aquawind]

Looking at the visable it lamost looks like ~14.5N 63W would have been a better point..little further north and maybe even east anyway..Major blowout this afternoon..look like a massive Tropical Wave today alrighty..

[rbaker]

ditto, a huge tropical wave that will pulse up and down till until it gets to w caribbean

[The Dark Knight]

Well.....We'll have to wait and see......

[Anonymous]

why is it that tropical waves usually gain convection during the night hours?

[lahurricanewatcher]

I wondered the same thing. I know that daytime heating usually causes an increase in convection over land. Why the difference?

[Anonymous]

the only thing I can figure since there is no daytime heating over water etc. that it must have something to do with the constant water temperatue and the cooler night air? I dunno maybe somebody will explain it here soon to us.

[Dean4Storms]

Most of it's problem till now is the forward speed in which it's moving. This along with the shear on it's northern periphery especially has caused it to outrun most of the convection once it re-fires. This reminds me of Claudette in alot of ways.

[Ola]

why is it that tropical waves usually gain convection during the night hours?

Daytime heating only occurs over land because land absorves sunlight and releases heat which warms up air above the surface a lot warmer than the air above and that makes the air rise, which then cools high up there and creates clouds.

Over water, it does not work like that because the sun rays travel through the water and it does not warm up the air above it, which is warmer than the surface of the ocean in the tropics or about the same. On the other hand, at night the water temp stays constant around 80 F in the tropics but the air cools, thus making the temperature difference to enable the air to rise like a hot balloon would, and the same cycle that happens with day time heating over land happens over water at night.

But, over land the heating is a lot more drastic, thus u get thunder storms over land in the tropics every day, but you dont just get thunderstorms over tropical waters every night unless there was something else to help with the lift like a deformation in the normall trade winds (thats what a tropical wave is, when u add up forward motion plus a curve u get acceleration) or an upper low to aid with ventilation and lift.

[Wthrman13]

Daytime heating only occurs over land because land absorves sunlight and releases heat which warms up air above the surface a lot warmer than the air above and that makes the air rise, which then cools high up there and creates clouds.

Over water, it does not work like that because the sun rays travel through the water and it does not warm up the air above it, which is warmer than the surface of the ocean in the tropics or about the same. On the other hand, at night the water temp stays constant around 80 F in the tropics but the air cools, thus making the temperature difference to enable the air to rise like a hot balloon would, and the same cycle that happens with day time heating over land happens over water at night.

But, over land the heating is a lot more drastic, thus u get thunder storms over land in the tropics every day, but you dont just get thunderstorms over tropical waters every night unless there was something else to help with the lift like a deformation in the normall trade winds (thats what a tropical wave is, when u add up forward motion plus a curve u get acceleration) or an upper low to aid with ventilation and lift.

Pretty close, but not quite. You are correct in saying that daytime heating of the land surface warms the air immediately above it, thus destabilizing the lower levels of the atmosphere, and depending on other conditions, making convection more likely. However, the reason there isn't as much destabilization over oceans during the day as over land is not just because the sunlight travels through the water (it actually doesn't get that far down, most of it is absorbed after a few dozen meters), but primarily because water has a much higher heat capacity than virtually any land surface. That is, it takes a lot more energy to raise the temperature of a given volume of water than a given volume of soil (or vegetation, or whatever land surface you are talking about). Also, you have mixing going on in the top layers of the ocean which helps to further decrease the diurnal temperature variation.

The reason that convection over the ocean often increases at night is due to cloud top radiational cooling, which cools the air immediately above the cloud top, while the air in the cloud maintains its temperature, so yes, the air does cool, but only significantly near the tops already existing clouds. This cloud top cooling destabilizes the air near the cloud, enhancing the convection.

There is a diurnal free atmosphere warming/cooling cycle, where the air far removed from the surface and clouds, over both continents and land, does cool off a bit from radiational heat loss at night, but this effect is very small compared to other processes and can usually be neglected.

[MGC]

Yep, water has a much higher specific heat than dirt. HeyWhrman13 are you a student at OU?........MGC

[lahurricanewatcher]

Thanks, Good explanations.

[Wthrman13]

Yep, just wrapping up my M.S. degree this week. Had my seminar this afternoon. Boy am I glad that is over!