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Tropical Storm Isaac, Part 1: Moving Through The Eastern Caribbean Sea


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This is probably already a TS, and perhaps somewhat stronger than 35 kt given the rapid forward speed and how strong the low-level westerlies are from the low cloud motions on the south side. It's also lost quite a bit of latitude today.

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This is probably already a TS, and perhaps somewhat stronger than 35 kt given the rapid forward speed and how strong the low-level westerlies are from the low cloud motions on the south side. It's also lost quite a bit of latitude today.

Its one of those things that the models don't seem to be catching is the south of due west movement and that could be important to track in the long run

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This is probably already a TS, and perhaps somewhat stronger than 35 kt given the rapid forward speed and how strong the low-level westerlies are from the low cloud motions on the south side. It's also lost quite a bit of latitude today.

Yep, agree. I've noticed it has been moving just a bit south of due west for the last 12 hours...it appears to be close to 15N, south of around 15.7N when it streaked for a few frames half a day ago.

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This would be a fascinating way for Savannah to finally get a landfall.

I think the fact that the OP on this run resembles it's earlier ensemble members runs lends it some merit for now. Time will tell especially once we get a fix on exact location for models to use.

EDIT: The end of the run has it go inland just a bit before being brought up the coast and over Hatteras to out to sea.

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This is probably already a TS, and perhaps somewhat stronger than 35 kt given the rapid forward speed and how strong the low-level westerlies are from the low cloud motions on the south side. It's also lost quite a bit of latitude today.

Agree. It certainly looks like its mixing out that dry air at last. Still a little bit of dry air intrusion on its western flank, but the ball of higher TPW nearly covers the entire circulation envelope, so its close to no longer being a problem.

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Its one of those things that the models don't seem to be catching is the south of due west movement and that could be important to track in the long run

In the short and medium range I agree with you. In fact, don't be surprised if we see a continued south of west component of motion until we get past the Lesser Antilles. The way the mid-level ridge is oriented currently actually favors this track if the storm becomes vertically aligned as the ridge is oriented ENE to WSW. In the longer range, the bigger players will be a weak east coast trough that might help to weaken the weakness enough for an additional northward component of motion. However, if the storm does track significantly further south in the next 24-36 hours, it might have a better shot at missing Hispaniola.

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94L is clearly deviating south of forecast tracks in the past 12 hours.

The best track shows a slightly south of due west (~265 degree) movement in the past 6 hours with a 0z position of 15.3N 48.8W. IR loop suggests south of due west movement or consolidation has brought the center down to about 15N 49.8W at 4z. These slight southward deviations are important as almost all recent guidance had 94L at or slightly north of 16N at 12z today.

Banding is increasing significantly, but we need to see if this trend continues beyond the diurnal max and can sustain itself for at least 12 hours.

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Note that the best track shows a slightly south of due west (~265 degree) movement in the past 6 hours with a 0z position of 15.3N 48.8W at 4z. IR loop suggests south of due west movement or consolidation has brought the center down to about 15N 49.8W. These slight southward deviations are important as almost all recent guidance had 94L at or slightly north of 16N at 12z today.

Banding is increasing significantly, but we need to see if this trend continues beyond the diurnal max and can sustain itself for at least 12 hours.

Agreed-- it is really significant. It always seems like a few tenths of a degree in latitude in the E or C Atlantic have major implications down the road in determining whether a cyclone threatens N American or fishes. And, as GaWx has pointed out in the past, E/C Atlantic cyclones with some S-of-W motion early in their lifecycles are much more likely to eventually impact N America.

So today's lost of latitude is interesting, to say the least.

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I think the chance of a total miss out to sea off the U.S. east coast is under 10% at this point.

The implications of a further S. track and an apparent intensification/vertical stacking trend (which would continue a slightly S of due W motion for the next 1-2 days, as Phil noted) are that 94L would be more likely to miss Shredderola to the south.

Agreed-- it is really significant. It always seems like a few tenths of a degree in latitude in the E or C Atlantic have major implications down the road in determining whether a cyclone threatens N American or fishes. And, as GaWx has pointed out in the past, E/C Atlantic cyclones with some S-of-W motion early in their lifecycles are much more likely to eventually impact N America.

So today's lost of latitude is interesting, to say the least.

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100%

A WELL-DEFINED LOW PRESSURE PRESSURE IS LOCATED ABOUT 725 MILES

EAST OF THE LESSER ANTILLES. THUNDERSTORM ACTIVITY HAS INCREASED

AND BECOME BETTER ORGANIZED NEAR THE CENTER DURING THE PAST SEVERAL

HOURS. IF THIS RECENT DEVELOPMENT TREND CONTINUES...THEN A TROPICAL

DEPRESSION COULD FORM LATER THIS MORNING. THIS SYSTEM HAS A HIGH

CHANCE...NEAR 100 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING

THE NEXT 48 HOURS AS IT MOVES WESTWARD AT 20 TO 25 MPH. THIS LARGE

DISTURBANCE COULD REACH THE LESSER ANTILLES BY WEDNESDAY...AND

INTERESTS IN THAT AREA SHOULD CLOSELY MONITOR THE PROGRESS OF THIS

SYSTEM SINCE TROPICAL STORM WATCHES COULD SOON BE REQUIRED FOR

PORTIONS OF THOSE ISLANDS.

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I think the chance of a total miss out to sea off the U.S. east coast is under 10% at this point.

The implications of a further S. track and an apparent intensification/vertical stacking trend (which would continue a slightly S of due W motion for the next 1-2 days, as Phil noted) are that 94L would be more likely to miss Shredderola to the south.

Ah, OK. Well that's even more awesome. :)

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I've been thinking for the past few days that 94L will eventually end up in the Gulf, whether via FL, Cuba, or possibly even the Yucatan Channel. The digging trough along/off the west coast of N. America this weekend into early next week teleconnects strongly to increased ridging over the eastern US. I see it as unlikely that there would be a weakness strong enough to shoot 94L northward like the GFS has been showing.

Ah, OK. Well that's even more awesome. :)

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