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Tropical Storm Isaac, Part 2: Isaac Moving Into The Gulf Of Mexico-Hurricane Warnings For Morgan City, LA/MS/AL & FL Panhandle To Destin, FL

Superstorm93

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turtlehurricane

turtlehurricane

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Rain beginning to really wrap around the "eye" over the past few hrs.

Decent convective bands wrapping in from the north and south, still not pretty but much better than yesterday. It's only been truly away from land for less than 12 hours so it's doing well imo. Radar velocities out of Key West also show this is becoming more impressive, solid 55-65 mph winds around the circulation.

post-645-0-81827500-1346001009_thumb.png

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CUmet

CUmet

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Are we certain that the size of Isaac caused the water temp drop? The high/low yesterday in Key West was 82/73 with NE winds all day averaging 15mph with gusts to 40. The water temp dropped 4F yesterday. Upwelling certainly occurred and likely due to Isaac's circulation, but isn't that more an effect of Key West being surrounded by shelf water than anything else? Once over the open water of the gulf, Isaac's size shouldn't matter as much as long as it is moving forward. Otherwise, how do we explain Katrina's strenghening when it was easily the same size as Isaac?.

The water temp drop occurs whenever there's strong surface winds, which causes mixing of cooler waters from below the surface. It happens with every TC such that the inner core hardly ever experiences the 86-87F SSTs that are present pre-storm. It is more exaggerated over shelf waters, and the drop in water temperature won't be as substantial over the open Gulf where there is more depth to the warm water. However, the stronger upwelling with larger systems is real, and it does rob the inner core of somewhat higher SSTs, but how much of an impact it will have is anybody's guess and is not well captured even in the coupled dynamical models.

Whether it will continue to be large and sprawled out, or whether it will develop a tight inner core is another unknown factor. For example, Ike had perfect large-scale atmospheric conditions, but because of its large size causing more upwelling and the extremely moist environment (which favors large TC size), it was unable to really spin up a tight inner core. The environment in Isaac's case is somewhat drier (which may actually be a good thing for TC intensity in this case), and the convection doesn't appear to be as sprawled out even if the wind field is.

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DopplerWx

DopplerWx

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As Brad Panovich pointed out, once Isaac gets past Cuba the inflow should improve drastically as the moisture no longer will have to traverse Cuba and with a well defined center and warm gulf waters we should see steady intensification over the next 12-18 hrs. D-max tonight should be very fun to watch.

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phil882

phil882

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The water temp drop occurs whenever there's strong surface winds, which causes mixing of cooler waters from below the surface. It happens with every TC such that the inner core hardly ever experiences the 86-87F SSTs that are present pre-storm. It is more exaggerated over shelf waters, and the drop in water temperature won't be as substantial over the open Gulf where there is more depth to the warm water. However, the stronger upwelling with larger systems is real, and it does rob the inner core of somewhat higher SSTs, but how much of an impact it will have is anybody's guess and is not well captured even in the coupled dynamical models.

Whether it will continue to be large and sprawled out, or whether it will develop a tight inner core is another unknown factor. For example, Ike had perfect large-scale atmospheric conditions, but because of its large size causing more upwelling and the extremely moist environment (which favors large TC size), it was unable to really spin up a tight inner core. The environment in Isaac's case is somewhat drier (which may actually be a good thing for TC intensity in this case), and the convection doesn't appear to be as sprawled out even if the wind field is.

Excellent post... I agree with everything said here.

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OUGrad05

OUGrad05

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But we've got other data suggesting barely a hurricane at landfall. I don't really think given all the potential issues at play that making an accurate forecast of landfall strength is possible. I'm not saying ignore it or anything but the strong TS seems to be every bit as likely a cat4 storm at this point. Strengthening over the next 24 hours may set the tone for landfall strength. I just hope people are paying attention to the forecast so they don't get caught off guard.

New discussion and advisory should be up shortly. Looking at the system on GR2A it looks to be moving almost due north at the moment with perhaps a slight westward component creeping back in again based on the last two frames. New dropsonde just showed up on my stream and it's 995mb.

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andyhb

andyhb

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HWRF peaks at 150 kt around 12Z Tuesday and shows a 140-kt LF at 18Z the same day. Surprisingly, it shows intensification after the storm leaves the highest OHC, which of course is highly unlikely, particularly with such a large TC as Isaac.

That's at 900 mb.

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DaculaWeather

DaculaWeather

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Looking at the system on GR2A it looks to be moving almost due north at the moment with perhaps a slight westward component creeping back in again based on the last two frames. New dropsonde just showed up on my stream and it's 995mb.

That's what I was thinking. I was looking at the Base Velocity loop and you can see the shift in direction, a very noticeable shift toward the north.

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turtlehurricane

turtlehurricane

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I've put my Isaac forecast for today on my blog. http://weather.schematical.com/

More or less echoing what everyone else is saying, landfall intensity is an unknown since we don't know how fast the inner core will organize, the exact wind shear situation, and how upwelling will come into play. Definitely a situation to be concerned about though, the scale seems to be tipped towards intensification.

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SN_Lover

SN_Lover

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DISCUSSION AND 48-HOUR OUTLOOK

------------------------------

AT 200 PM EDT...1800 UTC...THE CENTER OF TROPICAL STORM ISAAC WAS

LOCATED NEAR LATITUDE 23.9 NORTH...LONGITUDE 81.5 WEST. ISAAC IS

MOVING TOWARD THE WEST-NORTHWEST NEAR 18 MPH...30 KM/H. A WEST-

NORTHWESTWARD TO NORTHWESTWARD MOTION IS EXPECTED DURING THE NEXT

48 HOURS WITH A GRADUAL DECREASE IN FORWARD SPEED. ON THE FORECAST

TRACK...THE CENTER OF ISAAC IS EXPECTED TO MOVE NEAR OR OVER THE

LOWER FLORIDA KEYS LATER TODAY AND TONIGHT...AND MOVE INTO THE

EASTERN GULF OF MEXICO ON MONDAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 60 MPH...95 KM/H...WITH HIGHER

GUSTS. SOME STRENGTHENING IS FORECAST DURING THE NEXT 48

HOURS...HOWEVER THE LIKELIHOOD OF ISAAC BECOMING A HURRICANE BEFORE

IT REACHES THE FLORIDA KEYS IS DECREASING.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 205 MILES...335 KM

FROM THE CENTER. A WIND GUST TO 55 MPH...89 KM/H...WAS RECENTLY

REPORTED AT VIRGINIA KEY.

THE MINIMUM CENTRAL PRESSURE BASED ON DATA FROM AN AIR FORCE

HURRICANE HUNTER AIRCRAFT IS 994 MB...29.35 INCHES.

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LakeEffectKing

LakeEffectKing

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I'm an amateur, so take everything I say with a grain of salt, but at this point in time, I believe the pressure and satellite/radar imagery (the layout of the storm) is much more important than the current windspeed at the center... At least for future development it is more important. The fact that the pressure only dropped 1mb doesn't mean too much; however, the storm is much more impressive satellite imagery, which favors future strengthening. Hope I wasn't just stating the obvious to everyone :).

EDIT: Also, I've seen hurricanes strengthen from TS to cat 2 or 3 in a matter of 18-24 hours. So guesses on the final wind-strength on the storm based on the current strength are premature, in my opinion. (Of course, this does not mean that this storm will do that).

Welcome. Good first post. This is the time of year the GOM can provide ample energy and support for rapid intensification of a TS/weak H if UL's are good, organization is good, and no large T-Td spreads near the center or banding features. The fact that the core is in an organizational stage at this time with about 2 days until LF is a bit worrisome for the N/C GOM coast. IR/vis are improving...and with the HRWF now "seeing" a core, we are "seeing" the model hinting at very robust strengthening....look for the GFDL to also showing deeper solutions...

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