Monday, January 14, 2008

SPI Coastal Surface Low

click map to enlarge

I’m writing this posting a little bit in the dark – literally, because it’s cloudy and I haven’t turned the lights on yet. But the subject is a weather condition known as the coastal surface trough, a rather persistent feature that grows right off our waters and just to the south. Let’s get down and dirty with the scientific forecast:

ALSO...AS THE 500 MB LOW MOVES IN FROM WEST...BOTH THE GFS AND

THE ECMWF DEVELOP A PRETTY STRONG COASTAL SURFACE LOW TONIGHT AND

TUES WITH THE FEATURE ROUGHLY MOVING PARALLEL TO THE TX COASTLINE

INTO EARLY WED. THIS SURFACE FEATURE WILL ALSO HELP MAINTAIN GOOD

MOISTURE ADVECTION OFF OF THE GULF OF MEX AND LOW LEVEL CONVERGENCE

OVER THE BRO CWA ENHANCING RAIN CHCS. THE BIGGEST DIFFERENCES IN

THE MODEL SOLUTIONS SHOW UP IN THE TIMING OF THE MOVEMENT OF BOTH

THIS MID LEVEL AND SURFACE SYSTEMS.


Some locals would recognize this as being a forecast for sloppy seas, high winds, and definitely rain. The big driver is a mid-level low pressure zooming in from the west, although our friend the coastal low will drive it all the way to High Island on the Louisiana border. And the long-range forecast is for another coastal low to form later in the week as well, a rarity having two of them in one week.

Back to the map I posted above, it is very interesting because it shows a bunch of northern Mexico in good detail. Our friend the coastal surface low always forms parallel to the beach. The surface low usually forms as if by magic about 10 miles off the coast, mostly in the top two-thirds of the map where it looks like a bow. Nobody really knows why it forms, which makes it really cool.

Or at least I can’t explain it. My research has taken me to studies about the mountain effect of the Sierras, which didn’t seem right because SPI doesn’t have any, to gravity waves, but those satellite pictures didn’t resemble our friend in the least. Stuff about sea-breeze front was disappointing as well, although sometimes in the summer you can actually see the coastal surface trough because of the morning thunderstorms you can see way off to the east.

But enjoy the map, as at least I still have much to learn about the Mexico coast to our south. Note that the Laguna Madre down in Mexico is huge. Hurricane Emily bashed the entire area around San Fernando on the lower left. Dang coastal low can be downright ornery sometimes!

3 comments:

Will Davis said...

Interesting, and complicated, stuff. Above my pay grade.

I have always thought it is the typical southwestern wind from the Gulf? But I know it is, no doubt, much more complicated. Maybe in the end, weather, as they say, is simply unpredictable.

It is really nasty here in McAllen. Damp, cold, and cocoa-time, maybe "hot toddy" time.

Will

Sam said...

My point was it was easy to actually see a dark blob form off the horizon if you were looking out to sea off the beach, right here on SPI. I never say stuff right.

As far as sunny relaxed weather, I fear we're in for some cool drizzles but no big Canadian outbreak of cold. Trust me, that could come next week or after; at least it will try.

As to my favorite winter drink, I actually like to take a very hot shower and dress up all warm and comfy and get a tumbler with French vanilla ice cream and a really good whiskey, maybe a touch of nutmeg or cinnamon if I feel the urge. Otherwise, beer for me.

Let me know when you get back and feel like plunking some keys.
/s/

Will Davis said...

You bethca. I'll bring my guitar.

And I hear what you're saying about the dark blob.

Will