The link you're referring to what you see are called streamlines; it's common in tropical latitudes to use them because you don't see what we refer to in the met biz as dynamic lows and ridges which exist by baroclinic processes; differences between cold and hot in the atmosphere. In the tropics winds are usually very light and pressures don't vary too much at the surface. In the upper air, think of 850mb as 5,000 feet, 700 mb as 10,000 feet, 500 mb as 18,000 feet, 300mb as 30,000 feet. When you look at the particular chart you're looking at; there is no shear to speak of at 850 to 700mbs and you will note the streamlines are much more in line with the low and mid latitude flow below 10,000 feet which isn't indicative of a "developed" tropical system. Being that this system is relatively shallow, it continues to be steered by the low level winds this chart indicates. Satellite photos will also aid you in determining that too. Water vapor doesn't help unless you're talking about a vertically coupled system; that is the storm is stacked from bottom to top, and if so, it's steering is done by the flow at 500mbs and up. To get a picture of shear over the storm you need the main link: http://cimss.ssec.wisc.edu/tropic/real-time/atlantic/winds/winds.html Then go to Wind Shear http://cimss.ssec.wisc.edu/tropic/real-time/atlantic/winds/wg8shr.html When NHC talks about shear, this is the chart they're looking at, now when they mention shear below the outflow level, you have to look for something higher, like 400 mbs. These charts are vital in determining the environment these cyclones are in, and as you see as of this typing, the storm is in a fairly low shear environment now at that level, so if you go lower and look at http://cimss.ssec.wisc.edu/tropic/real-time/atlantic/winds/wg8midshr.html which is mid level shear, you will note the northerly component which NHC has been referring to and as you see, it's not low and it's not high, but more than likely just high enough to keep the storm somewhat decoupled at that particular column thus it remains a tropical depression at this time. To look at the satellite presentation currently, it appears it's winning the battle of the environment and as of this typing looks about as good as it's been in the past day or so, so don't be surprised if you might see an upgrade on the 5 am advisory, though NHC is pretty conservative when it comes to continuity; very rare will you see them radically leap in one advisory, unless a recon mission justifies it. I suspect you'll see a shift west and south but not too radical on thie next advisory.
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