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Isaac Early Monday Update - from WTVY-TV Meteorologist Oscar Fann

Here's your 2am cdt update on the latest on Isaac....
(a little late - these things take time...)
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CURRENTLY -

Issac's path has changed just a little - to a truer WNW direction (a compass has 360 degrees with north at 0 or 360)...for most of Sunday Isaac headed 285 degrees (true west is 275 degrees)..slowly over the last few hours Isaac has moved to a 300 degree heading (true northwest is 315).

No surprise there...I'm thankful Isaac stuck to its 285, or westerly heading on Sunday that place Isaac farther west than anticipated.

We can thank that upper trough in the northern Caribbean for 'tugging' on Isaac for that extended westerly direction (as well as keeping Isaac's flow disrupted).

While there is time, note on the radar loops of Isaac the lack of convection (radar returns) on the south side of the center of Isaac.

That's the influence of the dry air the Caribbean trough has injected into Isaac for the last 2 days..but as I mentioned...that dry air entrainment looks to be cut off as the distance of Isaac from that trough increases.

Isaac has actually been in a favorable environment for strengthening over the last 2 to 3 days, but apparently that pesky Caribbean trough full of dry air has disrupted moisture flow (the fuel for tropical systems)into Isaac. It's like cheap gas instead of high octane fuel that Isaac wants...sputter, sputter..choke..choke..BUT..NO MAS!

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LATER TODAY (MONDAY) -

Unfortunately later today, things figuratively and literally 'heat up' for Isaac.

The Caribbean trough is pulling away to the south, freeing Isaac from its (the Caribbean) trough's disruptive influence.

Now, Isaac has an unfettered run through the central Gulf ahead of it.

In Isaac's path is that high octane fuel...87 to 90 degree Gulf Loop Current water (although the better concentration of that warm seawater lies to the southwest of Isaac's path).

By Monday afternoon look for Isaac to become a hurricane and watch its center, or eye, become better defined. Once that starts happening, the hurricane's overall organization should quickly improve, and we begin to worry about rapid intensification.

The official National Hurricane Center (NHC) still calls for a Cat 2 hurricane at landfall (more on landfall in later)...but as I mentioned in an earlier post, intensity forecasts are not very good - especially if a hurricane undergoes rapid strengthening).

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FORECAST PATH AND LANDFALL -

The latest hurricane model output has NONE showing a landfall east of the Alabama / Florida line.

Only ONE model (not one of the primary reliable models) out of nearly TWO DOZEN shows a landfall around Gulf Shores.

Yesterday's ECMWF model (one of the primary models) that was showing a similar Ala / Fla line landfall now has SHIFTED WESTWARD also, to a Mississippi landfall near Gulfport.

Other notable models (GFDL, AVN, MRF) also stick to a southeast Louisana or a Mississippi / Louisana landfall.

The GFS (the other primary model) has stuck to some type of Louisiana landfall for over 48 hours now...very consistent.

The GFS is showing a recent trend of having Isaac hit the southeastern Louisiana coast south of New Orleans..then move west slowly along the coast (a sign that the steering high pressure to the north had it pinned down, so to speak).

A new wrinkle has formed from the GFS - now, Isaac still makes landfall south of New Orleans...moves west briefly along the coast...then moves northwest through western Louisiana and heads up the Texas / Louisana line into extreme eastern Oklahoma then curves east into southwestern Missouri.

The GFS is saying that's where the steering ridge ends, so Isaac would travel around the steering ridge (again, high pressure winds rotate clockwise). If this proves true..that's where the extremely dry summer occurred - an almost perfect scenario.

REMEMBER, the NHC official landfall location for Isaac is now in southeastern Louisiana, across New Orleans and up the Mississippi River. We have seen a continual westward shift of the landfall location since early Sunday morning.

I won't go over local effects of Isaac again..you can find them in previous posts as well as numerous other stories our reporters have done on our home web page (as well as the hurricane page for preparation advice).

Be Safe...

Oscar
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NOTE:
Just before 11pm cdt Sunday evening...

The latest National Hurricane Center (NHC) update provides more apparently good news, regarding:

current direction (still moving just north of due west);
landfall (farther west to southeast Louisiana Tuesday night);
delayed intensification (dry air to the south interfering with flow).

I will have another update posted here at around 1 am cdt Monday Aug 27 (about 2 hours from now)...the title will change and have Monday in the title - so you will know...see you then...Oscar

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(earlier Sunday evening post follows)

Let me clarify the watches and warnings for the Florida panhandle counties and coastline.

HURRICANE WARNING -
is in effect for Okaloosa county WESTWARD to Louisiana...
(this includes Destin and the coast to the WEST toward Louisiana)

HURRICANE WATCH -
is in effect for the Florida panhandle coast for south Walton and coastal Bay and coastal Gulf counties

TROPICAL STORM WARNING -
is in effect for the coast EAST of Destin through Apalachicola and for all of the Apalachee Bay area. INCLUDED are the counties of Walton, Holmes, Washington, Bay, Gulf, Franklin, Calhoun and Liberty.
(For now, Jackson and Gadsden counties are NOT in the tropical storm warning area).

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Now, comments on the forecast track of Isaac -

Isaac has indeed moved more westward today, and this helps put more credence into Isaac's future forecast path.

(UPDATE - the new 8pm edt Aug 26 Isaac update shows this basically westward motion is continuing for now)

I think this primarily westward movement we saw today (and is still occurring) bodes well for the forecast landfall area late Tuesday for either:

1) the Louisiana / Mississippi area (the National Hurricane Center's official landfall area; or

2) south of New Orleans along the southeast Louisiana coast then slowly westward along the Louisiana coast.

(NOTE: This is an even further westward placement for the landfall since this morning's initial westward shift)
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The two main concerns for the WTVY-TV area are:

1) storm surges and coastal flooding;

2) excessive rains and stream flooding.

The current landfall area of near the Ms/La border STILL HAS SIGNIFICANT implications for areas to the east, all the way through Mobile, Pensacola, Destin, Panama City, Apalachicola into the Apalachee Bay area (Carrabelle, St. George Island, Alligator Point).

These coastal areas face storm surges of 6 to 12 feet (from Destin westward) and 4-7 feet east of Destin.

These water levels are in addition to normal high and low tides..by the way, over the next few mornings, high tides are occurring around 6 to 10 am local time. This would be the time storm surges would have the most effect.

For now (with the La/Ms path) the heaviest rains will be consistently along and south of I-10 in the Florida panhandle.

Inland areas such as south central and southeast Alabama as well as southwestern Georgia could have excessive rains, but more of a sporadic nature (off and on torrential downpours).

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A REMINDER -

BE AWARE of old, large trees near where you live. The age of these trees with the dry weather earlier this summer may have weakened them..THEN the above average rainfalls this month may have loosened their root structure.

High winds (even only gusty winds to 30 - 40 mph) may be enough to topple some trees. Over the next several days, take note during the day of all such trees near your house to see if you notice any change in appearance, such as if there's more of a lean to them.

EXPECT POWER OUTAGES..hopefully they will be of a short term, isolated nature..regardless, don't be surprised if you lose power at some point through midweek, especially closer to the coast.

A TORNADO THREAT will exist beginning late Monday through at least part of Wednesday, but it's too early to be more specific on this, except the tornado threat will be higher in the Florida panhandle.

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MORE ON ISAAC's PATH...

If Isaac take the route to southeastern Louisiana then moves slowly west along the Louisiana coast, this would reduce many of our weather related concerns after Tuesday night.

We should know if the few holdout weather models (which try to take Isaac more northward to the Alabama / Florida border) will change their forecast after ingesting the new data showing Isaac took a more westward motion for most of the day today. A potential landfall say near Gulf Shores would change everything for the worse for all of us in the WTVY-TV area.

AGAIN, the Alabama / Florida landfall area is NOT the forecast path for Isaac. The trend for the last 24 to 48 hours has consistently been to either the La / Ms border area or to the Louisiana coast then westward.

I'll have another update later tonight. Keep your fingers crossed.

Oscar
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4AM CDT SUNDAY AUG 26 ISAAC UPDATE

The 4am complete update has arrived from the National Hurricane Center (NHC)…and here’s the news (you can find the full NHC update under an accompanying article on the Home and Weather pages)…

Isaac is slightly stronger (65 mph, still a tropical storm), but here’s the important change…

The NHC has indeed shifted Isaac’s path significantly to the west.

This shift is actually farther westward than I anticipated – given the conservative nature of the NHC. Nevertheless, it is justified, as I already pointed out (in a detailed article on our home web page in addition to Connor's earlier article), the trend has been there from 12 to 36 hours.

An eventual shifting even farther westward is possible later Sunday or Monday (unless, of course, ridge and trough positions change, along with the steering winds for Isaac).

The current forecast landfall is near Dauphin Island and Mobile Bay around 2am cdt Wednesday Aug 29…still as a Category 2 (sustained winds near 105 mph).

Also, Isaac may move a little faster through the Gulf than previously thought. That could be bad and good news. A faster moving Isaac could create more tornado potential as its winds reach inland areas. However, the faster movement may also work to hold excessive rain totals down.

The longer soon-to-be Hurricane Isaac remains over the Gulf, the greater chance the intensity increases. (The NHC would be the first to tell you intensity forecasts for hurricanes leave much to be desired, especially in rapid intensification modes). Isaac will pass over very warm central Gulf waters, but Isaac should miss the warmest water that lies in the south central Gulf.

IF THIS NEW FORECAST PATH HOLDS, this is what we can expect for the WTVY-TV area:

Hurricane Watches (already in effect) for the nearby coast..

Hurricane Warnings still likely from Apalachicola westward..

Tornado Watches for all of the Florida panhandle..southern and southeastern Alabama and probably southwestern Georgia.

There will be other watches (ESPECIALLY FLOODING POTENTIAL – 3 to 7 plus inches of rain still likely), warnings and advisories to come..

In short…CONTINUE PREPARATIONS in case the path changes yet again…STOCKUP ON SUPPLIES..PUT GAS IN YOUR VEHICLE..GET CASH from the bank / ATM..

REGARDLESS….BE PREPARED FOR POWER OUTAGES..DOWNED TREES AND POWERLINES..

The recent NHC update on Isaac is good news, but the danger potential remains.

Oscar


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