Tropical Depression Isaac:

[ticka1]

I am not bashing anyone - I just making a statement. Time will tell like it always does. Watching Isaac with both eyes open now!!! Thanks for the replies.

[djjordan]

When this thread first started it had a very powerful Hurricane just offshore of SE Texas by 9/1. That was last week. LOL.

[cperk]

I will agree with that JG.....lets not forget the EURO sniffed a far west solution for mnay days until it caved to form a consensus....since that time the GFS decided otherwise.....this 0Z package is going to be fun to watch....the 18Z GFDL already into SW LA and very close to the TX/LA border....

oh and about 3 days ago the GFS even sniffed a upper Texas coast hit....

Glad to see you back posting over here,we can certainly use your knowledge.

[skidog40]

its either the keystone light or did i see wsw movement

[Paul]

its either the keystone light or did i see wsw movement

its wobbling ,plus there is still some internal issues with the MLC and LLC not exactly aligned...

[jeff]

its either the keystone light or did i see wsw movement

its wobbling ,plus there is still some internal issues with the MLC and LLC not exactly aligned...

LLC is clearly moving WNW

[Bluefalcon]

its either the keystone light or did i see wsw movement

You can see the COC on the Key West radar...If anything the COC looks to be difting North. A Hurricane hunter and a NOAA P-3 are flying through right now...both are getting center fixes.

[jgreak]

Sunday Evening Update from Jeff:

At 400pm a Hurricane Warning is issued from Destin, FL to Morgan City, LA including Lake Pontchartrain and metro New Orleans.

State of Emergency declared for the City of New Orleans.

Discussion:
Isaac enters the Gulf of Mexico, now passing 40 miles to the SSW of Key West. Radar data from Key West shows that there has been little intensification through the day, but recently thunderstorms have developed near/over the center and Isaac may be on the verge of intensification as the central pressure today has been falling slowly. Isaac continues to move rapidly toward the WNW at 16-18mph and this motion should continue for at least the next 24 hours closing the preparation time along the northern Gulf coast.

Track:
There has been little change this afternoon with respect to the spread in the model guidance. The GFS continues to be far to the west with a landfall SC LA and then a track toward the WNW or W after landfall toward E TX. The ECMWF has trended slightly eastward from the FL panhandle to near Mobile, AL, but still is well to the east of the GFS. The HWRF and GFDL show a landfall into the central LA coast while the CMC is toward MS. Both the GFS and ECMWF ensembles continue to cluster over Louisiana suggesting that the operational run of the GFS may be too far west and the ECMWF operational run too far east.

The differences all appear to be in the handling of the trough and ridge pattern over the US and how far south the SE US trough digs and if it captures Isaac. It is becoming increasingly likely that this trough does not dig enough to capture and turn the system northward (a landfall over the FL panhandle). However this trough produces a weakness allowing the system to turn toward the NW and gain latitude. The GFS continues to differ as Isaac approaches the coast and builds a strong ridge in from the ENE sending the system WNW to W along the entire southern Louisiana coast…this seems a little unlikely since none of the other models are showing anything similar after landfall. A better consensus approach at this point is to level the GFS out toward the NW after landfall which brings it closer in line with the GFDL and just to the west of the HWRF. The ECMWF is an eastern outlier currently, and I do not see Isaac moving that far north and east.

While there remains a larger than normal amount of spread and uncertainty beyond 48 hours, the window for preparation and decision making is closing. Hard decisions with respect to evacuations and preparations along the LA and MS coasts are going to have to be made with the available data and the amount of uncertainty at hand.

On the current NHC forecast track Isaac will make landfall very near the SW coast of MS late Tuesday or Wednesday morning very near or slightly east of where Katrina hit in 2005. Only a very small shift west will bring Isaac directly into Lake Pontchartrain.

Intensity:
There is little change in the intensity forecast with the system expected to become a hurricane on Monday and reach category 2 intensity prior to landfall. Conditions in the Gulf of Mexico look very favorable for intensification with near excellent upper level outflow and warm water. In fact the more westward track currently depicted allows Isaac to cross over increasingly deeper warm water. The HWRF continues to produce a much stronger hurricane with the pressure falling well into the 940mb range. For now will go with a more conservative approach and in line with the rest of the intensity guidance and cap Isaac off at 100mph prior to landfall. It should be noted that the intensity forecast in the longer range periods can be off, sometimes significantly due to the limited skill in forecasting intensity.

Note: Isaac is a larger than average tropical cyclone that has far reaching effects and impacts. DO NOT focus on the exact track of the center, but instead the overall region of impacts. THE ERROR CONE does NOT indicate the potential area of impacts. Due to its large size, Isaac will be capable of moving a large amount of sea water (storm surge) toward the northern Gulf coast and the current landfall location is extremely surge prone from a hurricane coming from the S or SE.

Impacts:

Preparations to protect life and property should be underway in the Hurricane Warning area.

Storm surge values of 4-8 feet above ground level are currently expected over SE LA and coastal MS, these values may need to be increased to around 10-12 feet as the potential event closes in on the coast. Values are expected to be similar to Gustav in 2008, but below levels experienced with Katrina in 2005. Some areas, especially outside of hurricane protection levees will be deeply inundated and the proper actions must be taken.

Rainfall amounts of 10-12 inches is likely along and to the east of the track of Isaac with isolated totals to 15 inches possible over MS and AL. The potential for the storm to slow as it moves inland over LA may result in the increase of some of these totals.

Winds of 65-95 mph will be likely over SE LA and coastal MS/AL as Isaac moves onshore. Tropical storm force winds will onset hours before the center arrives at the coast, and this must be factored into any preparation plans. A hurricane warning means hurricane conditions are likely in 36 hours. TS force winds will likely onset on the coast of extreme SE LA by late afternoon Tuesday and then all across SE LA and MS/AL by mid evening including metro New Orleans. The worst of the winds will strike the coast overnight Tuesday into Wednesday morning.

[JackCruz]

I read a discussion elsewhere that if it doesn't turn north by tomorrow afternoon, Houston and Beaumont will be on the table as possible landfall locations. Opinions anyone?

Do you think a north turn is likely by tomorrow afternoon? Anyone? Is there a chance it can continue its westward movement until tomorrow afternoon...can it hold that path for so long?

[srainhoutx]

its either the keystone light or did i see wsw movement

its wobbling ,plus there is still some internal issues with the MLC and LLC not exactly aligned...

LLC is clearly moving WNW

Yes, it is.

[jeff]

I read a discussion elsewhere that if it doesn't turn north by tomorrow afternoon, Houston and Beaumont will be on the table as possible landfall locations. Opinions anyone?

Do you think a north turn is likely by tomorrow afternoon? Anyone? Is there a chance it can continue its westward movement until tomorrow afternoon...can it hold that path for so long?

I see no north turn tomorrow. With the GFDL and HWRF shifting west into SW LA, concern is growing for a track toward SW LA or even SE TX.

[biggerbyte]

Ditto! Major concern for a Rita like, or worse, track.

[Paul]

its either the keystone light or did i see wsw movement

You can see the COC on the Key West radar...If anything the COC looks to be difting North. A Hurricane hunter and a NOAA P-3 are flying through right now...both are getting center fixes.

most likley that is the MLC....due to southernly shear...expect the LLC to align with the MLC at somepoint after shear abates...ranification of another relo south....means further west than what is predicted....just some food for though if it does indeed relocate...

[biggerbyte]

Shear is exactly the problem.

[srainhoutx]

Slight shift W with the 00Z Tracks.

[wxman666]

Question for Jeff: Do you think that *if* we have a scenario where this thing actually heads towards the TX coast we will still be looking at a Wed/Thu landfall or sometime later? Or is it still too early to tell?

[Rip76]

Man, the names at the bottom are lit up like a Christmas tree.

Paul, great to see you back.

Did a little canned good, battery, and water prep today.

[jgreak]

Question for Jeff: Do you think that *if* we have a scenario where this thing actually heads towards the TX coast we will still be looking at a Wed/Thu landfall or sometime later? Or is it still too early to tell?

Not sure what to make of it, but wunderground has an 80% chance of thunderstorms on Thursday for Houston. I don't recall any rain being in the forecast earlier in the day for this week.

[biggerbyte]

At one point we had 104 guests.

[cisa]

Question for Jeff: Do you think that *if* we have a scenario where this thing actually heads towards the TX coast we will still be looking at a Wed/Thu landfall or sometime later? Or is it still too early to tell?

Not sure what to make of it, but wunderground has an 80% chance of thunderstorms on Thursday for Houston. I don't recall any rain being in the forecast earlier in the day for this week.

I was just noticing that myself.