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New computer model runs for Katrina

By: Dr. Jeff Masters , 7:11 PM GMT on August 25, 2005

The 1:18pm EDT Hurricane Hunter mission found the pressure of Katrina remained constant at 990mb, but the maximum winds were now on the northwest side at 64 knots (73 mph) at the airplane's flight level of 5000 feet. Radar from Miami confirms that the north side of Katrina has greatly increased in the amount and intensity of precipitation the past two hours as the storm continues to strengthen. It is a very good thing that Katrina does not have an extra 12 hours to intensify before landfall! However, the very favorable environment for intensification that Katrina is currently in is expected to still exist once she is in the Gulf of Mexico Saturday. I expect Katrina will become at least a Category 2 hurricane before its second landfall.

The latest computer model runs, performed using the 8am EDT upper air data, have made a major shift. Katrina is expected to push much farther west off of the western coast of Florida, and make a delayed turn to the north. These latest model runs show a much reduced risk to Tampa, and put an area from New Orleans to Cedar Key, Florida at risk. In the center of this risk area lies the U.S.'s very own hurricane magnet, the Pensacola region, where Ivan and Dennis struck.

Katrina continues to intensify at a modest pace, and if present trends continue will hit Florida near Fort Lauderdale tonight as a minimal Category 1 hurricane with 75 - 80 mph winds. The northwest side of the storm continues to suffer from dry air intrusions, and the primary intense thunderstorms and strongest winds are on the south side. Thus, the usual rule about the right front quadrant (north side) of the storm being the most dangerous is not neccesarily the case with Katrina. The highest storm surge will still be to the north of where the center comes ashore, but wind damage may be equally distributed on both sides of the storm.

The Miami radar loop continues to show an increase in low-level banding, and an eye-like feature trying to form. Upper level outflow is improving and slowing expanding.

As I discussed in the previous blog entry, the major threat to South Florida from Katrina is freshwater flooding from her rains. Rainfall amounts of 6 - 10 inches are expected from this slow-moving storm. For comparison, Hurricane Irene of 1999, which hit South Florida as a Category 1 hurricane, dumped 10 - 20 inches of rain. Damage from Irene was over $800 million in Florida. Damage from Katrina will probably be much lower, in the $30 - $100 million range, since Katrina's rainfall will be half of what Irene's was.

What's that behind Katrina?
A large area of disturbed weather even bigger than Katrina lies to her east, just north of Hispanolia. This disturbance lies in an area of high wind shear of 25 - 35 knots, and is not a threat to develop into a tropical depression in the next few days.

Katrina blogs
For observations of what's happening now in South Florida, we have several bloggers writing today:

turtlehurricane (Weston, Broward County)

sngalla (Fort Lauderdale)

MrJ76 (Okeechobee)

Zeenster (Cape Coral, SW Florida)

evolution (Charlotte Harbor, SW Florida)

Dr. Jeff Masters


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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192. cajunkid
4:26 PM EST on August 25, 2005
looks like she is going south along the coast
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191. Jedkins
9:27 PM GMT on August 25, 2005
The rain fall rate is 5 to 7 inches per hour in the eyewall feeder bands at 2.50 to 5 inches per hour.
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190. caneforecaster
9:26 PM GMT on August 25, 2005
I have to say, the weenie in me is enjoying this thoroughly.....(in Miami!)
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189. leftyy420
9:22 PM GMT on August 25, 2005
ok here is a easy version.

that dry stable air is idictive of a ridge and at its currently location it is weakly sterring katrina on a westward motion. you ned to know the layout of the ridge to know where the axis is cause once you pass the axis motion will change. if you look at a loop you can see where moistiure is lowinf to and from. this gives you and idea of the steering currents. now currentyl a trof has devloped south of katrina and is inducing a southern component. but the easiest thing to do is look at the water vapor loop in conjuction with a ir or visible loop and you can see the likley steering of the storm. at this time you will not be able to comprehend the steering of this sytem 3 days from now cause everything you see will change and iteract with each other. the models can figure all this out with an error of course and shift the steering currents. thats a quick and easy explanation no more talk on track in the longterm. the storm is blowing up off the coast and you guys are missing it all
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188. HurricaneKing
9:25 PM GMT on August 25, 2005
What raindancer said.
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187. butterflymcb
9:24 PM GMT on August 25, 2005
New to the site...Hi guys. Been reading for months now...but I have to join in today.

Anyone see the eye really forming on the last few frames of the radar? (Miami NOAA) Am I seeing things? I am an amateur.
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186. cjnew
4:25 PM CDT on August 25, 2005
lol..yes definately.....i would think that even if there wasnt a hurricane..no offense
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185. OneDay
4:17 PM CDT on August 25, 2005
It seems that historically when the models unanimously make a large shift in one direction (like they did today,) future runs continue the trend often all the way up to landfall. (I know this time it is due to the better initialization because of better data.) Is this indeed what normally happens?
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184. raindancer
9:24 PM GMT on August 25, 2005
You should be thinking, "Wow, I'm glad I don't live in Lauderdale!"
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183. cjnew
4:21 PM CDT on August 25, 2005
hey everyone!!! im here in panama city fl...what should i be thinking at the momoent..lol
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182. Joshfsu123
9:20 PM GMT on August 25, 2005
Absolutely... It's always good to have open discussion leftyy and different opinions... =0)

I think things will start to become clearer once it gets off the coast of Florida into the Gulf. So I agree, let's just focus on the landfall.

Good discussion though.
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181. StormJunkie
9:19 PM GMT on August 25, 2005
Lefty- Will you do me a favor? Get online for a minute so that you can explain the water vapor to me. I see the dry air that is N of Katrina, but I would like to understand how it is steering Katrina.
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180. leftyy420
9:20 PM GMT on August 25, 2005
the gfs is always the most stubborn model any way lol
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179. leftyy420
9:18 PM GMT on August 25, 2005
well i put weight in the gfdl now cause its the only model to forcast a southern movement. she is moving wsw or sw at best now. but comeon yall lets get off the track issue. we will have more models in a coupleof hours and landfall occuring soon. but good disscussion and views everyone
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178. GetReal
9:16 PM GMT on August 25, 2005
The GFS is unreliable, three days ago it did not even pick up on this system. So according to the GFS Katrina should not even exist.
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177. Joshfsu123
9:01 PM GMT on August 25, 2005
The GFDL also forecasted and still does a South Florida Keys landfall up to this morning. That model has a more Southern bias than what will happen and thus, that would would support a more westward movement.

Like I said, it's all guess work at the moment.

BTW, in the NHC Discussion, they stated that the GFDL and the GFDN models that take the system farther West are being given LESS Weight because they are moving the system faster. That is my opinion as well. The GFDL model has this Hurricane moving at about 10-12 mph whereas it is only moving between 5/6 mph.... That makes a big difference because 1) it won't move as far west as forecasted by these models and 2) the TROF will dig down and move this system more North than they forecast.

They also state that the GFS has been most accurate, which is correct, and thay the GDFL has been flip-flopping.

Can these models be correct? Absolutely, especially if this system picks up some speed over Florida and if the 18Z and 00Z runs show this, maybe it can start to be noticed. However, the discussion also included 18Z information that supports a landfall near Apalachicola.
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176. leftyy420
9:15 PM GMT on August 25, 2005
good disscussion and i feel confident we will see panhandle landfall of a cat 2-cat 3 hurricane
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175. sSnack
5:16 PM EDT on August 25, 2005
Updated my blog here: North Miami Beach

Conditions continue to deteriorate, and we just got a hurricane force gust.
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174. raindancer
9:13 PM GMT on August 25, 2005
Wow - look how the dry air has nearly vanished in the last few frames - really winding up here at the last minute!
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173. leftyy420
9:12 PM GMT on August 25, 2005
only the gfs and bamm tend to a ne movement and they only do that as a first movement after west. just be patient and watch the next 2 to 3models. i suspect we will see lotmore concensus with each model run and i am done disscussing it. we all have our own veiws for our own reasons. but the westward shift is the trend so any change would likely reflect that
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172. leftyy420
9:10 PM GMT on August 25, 2005
usually major hurricane stauts andit doesn;t make its own steering currents, just it isn;t easily steered by a weakenss or weak trof. they tend to move in the direction the are headed thur the shirt term, also she isn't forcast to be but a cat 1 or weak cat 2 by the gfdl by the turn and it weakens her right befor landfall as a ct 2. think that right now all models are underestimating the water temps and she could honestly be even a cat 4 but thats as bout high as i could see. i want to wait and see what is left og her after landfall to say for certian what her final strength in the second land fall would be
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171. StormJunkie
9:01 PM GMT on August 25, 2005
Lefty the N turn will not come for three days. What I am saying is that the recon that you are relying on can change. I agree that over the next three day the W movement will be much more than expected. After that your guess is as good as mine. But the middle of the road between the models is the best bet. All models do trend to an E motion at some point. Now where that happens remains to be seen. The GFDL did not pick up on the WNW/W turn for Florida where it should have and that is what bothers me about this model. While it could she still could make it south to the keys but I do not see it. That is why I am not convinced about the E turn that the GFDL misses. For several days the GFDL did not get that she was not going through the keys. And these were the pas t 4 or 5 runs. Iexpect models to be that far off three and four days out, but not 12 to 36 hours.
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170. Weatherwatcher007
9:10 PM GMT on August 25, 2005
Katrina's pressure dropped 5 mb between the update and the new advisory.
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169. raindancer
9:10 PM GMT on August 25, 2005
Discussion is out - they agree with the slightly southward movement - and definitely strengthening now.
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168. leftyy420
9:08 PM GMT on August 25, 2005
she is probly near 80-85mph strength and we could see more in the next couple of hours right befor she finally moves on land.
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167. cajunkid
4:08 PM EST on August 25, 2005
how strong does it need to get make its own stearing currents?
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166. raindancer
9:07 PM GMT on August 25, 2005
lefty - I would agree that in the last 30 minutes, Katrina's presentation has improved dramatically and the eye has dropped south considerably.
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165. WSI
9:07 PM GMT on August 25, 2005
Based on wind estimates and precip on the radar, it looks like she is moving onshore now.
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164. leftyy420
9:07 PM GMT on August 25, 2005
she is really getting stronger looking on radar now
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163. cajunkid
4:04 PM EST on August 25, 2005
I hope I'm wrong, but it looks like the track favors a westward shift.
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162. OneDay
4:04 PM CDT on August 25, 2005
I am really itching to read the NHC 5 pm discussion......
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161. STORMTOP
9:04 PM GMT on August 25, 2005
you got it get real.......
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160. tshizzle
9:03 PM GMT on August 25, 2005
gettin windy here in Sunrise
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159. leftyy420
9:03 PM GMT on August 25, 2005
but that all changed after the recon flight. it lifted northward slightly and now the storm is moving south
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158. STORMTOP
9:00 PM GMT on August 25, 2005
JOSH THE NHC WILL CHANGE THE CHART AT 5PM AND AGAIN AT 11PM...YOU WILL THEN SEE A PRONOUNCED SHIFT TOWARDS THE WEST..your trough will not make it down here if you look at the wv loops you will see why..the 2 highs are bridging together right over the se coast thats why katrina is now moving more on a south component to it...
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157. GetReal
8:48 PM GMT on August 25, 2005
Just finished watching the latest water vapor loops for North America. It does not appear that the earlier referenced TROF is NOT digging southeast. In fact the TROF appears to be riding a zonal path over the ridge in the southeat U.S. The high pressure ridge appears to be holding in place. It appears this TROF will pass far to the north over the Great Lakes. Maybe this is what the westward leaning models are picking up.
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156. leftyy420
9:02 PM GMT on August 25, 2005
yes she has, just as the gfdl said she would once more that gfdl is falling in line
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155. OneDay
3:58 PM CDT on August 25, 2005
It seems the entire precipitation field of Katrina has shifted markedly to the south in the past several long range Miami radar frames, even if the center has only slightly dropped south.
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154. StormJunkie
8:58 PM GMT on August 25, 2005
Lefty the GFDL had this thing going through the keys 2 days ago. Prior to that it had a pretty accurate coarse for what is going on now. But I am not sure where it go the Keys thing. I see her go through the keys I will give the GFDL its respect.
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153. leftyy420
8:57 PM GMT on August 25, 2005
the models didi not the recon storm. one day yall will listen to me lol. i told u guys 2 days ago, i support the gfdl for this and all other models have come intoline with it for atleast the next 2 days. the gfdl shifted slightly thru 2 days but all the rest made major shifts. the ukmet now shadows that gfdl model that i used to call a southern fl landfall 2 days ago. trust me i wouldn't talk about track but i for one belive thst with all the data the models can do their job and thats my feeling on the models. with the irght data so u fly recon gather the data and now u guys all want to fight this westward trend. beware all of u who live in al miss or the florida panhandle
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152. FrankieSC
4:58 PM EDT on August 25, 2005
Just for future reference...Orbit White Gum in Bubblemint flavor is really good for clearing the taste of crow...Which I have not eaten, YET!
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151. Joshfsu123
8:52 PM GMT on August 25, 2005
I know that but I also know that this system will turn North and Northeastward in time because of a TROF that is dropping down from the west. How far west will determine a Panhandle landfall or a Big Bend landfall but I still agree with Steve Gregory that a NE Gulf Coast landfall is likely.

So the fact that it is 4 days out still makes your forecasts just as unreliable as the rest of ours, including my own. I will stay with the NHC for now and if they shift west, I will too.
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150. leftyy420
8:54 PM GMT on August 25, 2005
first thing u must understand that the models get better every year though not oerfect. fran was what in 98, hugo was what 88. come on people, and we aren't talking regular model runs. the flew planes to gather this data. that gives more info and better runs. some of you are still holding on to the gfs theory and of all the models the gfs has shifted more than any. mark my words. al, miss,fl panhandle, like dennis, like ivan atleast cat 3
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149. StormJunkie
8:53 PM GMT on August 25, 2005
I was wondering about that Josh. Lefty- Did the 8am recon take in to account the weaking ridge due to the front or becuase it has not started to weaken yet it did not catch that part.
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148. leftyy420
8:53 PM GMT on August 25, 2005
yeah,all i am expecting here in va is some good rain and than some humid air lol
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147. StormJunkie
8:50 PM GMT on August 25, 2005
I agree with what you are saying wild. I went through Hugo which was supposed to be in NC. I watched people sit in traffic for 24 hrs prior to Fran who was supposed to hit here. I have stated that the models will shift again and where I am not sure of. No foot in mouth.
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146. willdd1979
8:49 PM GMT on August 25, 2005
it just might drench us here in NC with rain junkie but it's been dry here not really wet like in SC and I'm in Ft. Bragg/Fayetteville, NC.
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145. leftyy420
8:47 PM GMT on August 25, 2005
u must remeebr the nhc is in no hurry to change the track west yet.its 4 days away. you must understand there focus is short term not long term right now.once landfall occurs u will see the diff track, as well as after the next model runs
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144. OneDay
3:47 PM CDT on August 25, 2005
5 pm EDT maps are out on Wunderground...75 MPH, gusts to 90, she has actually dropped .1 degree in lattitude since last advisory.
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143. FrankieSC
4:43 PM EDT on August 25, 2005
Okay, I'll stifle my elation for a short while, but from past experience she would have to take a major turn to the northeast to avoid being deflected by the mountains. In the extrememly active season last year, that is what happened each time...I'm just saying...And you can't argue with, "I'm just saying"
Wildd - what part of NC do you live in? Wouldn't it be a giggle if it did turn to the Northeast and drench you too? :-)
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142. leftyy420
8:46 PM GMT on August 25, 2005
the further west she would go the whole track would shift west. it would put u at less of a threat
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