ATL GUSTAV: Tropical Depression - Discussion

[Cape Verde]

I think we can safely say that that the odds are extremly high that Gustav will hit somewhere in the US as at least a Category 2. There is some minor chance that it could hit Mexico.

All the deviation from that prediction is for the worse.

So, this is a serious system.

[weatherguru18]

Not sure if this has been posted yet, but the State of Texas is now activated Emergency plans for a major hurricane.

ftp://ftp.txdps.state.tx.us/dem/sitrep/ ... 082608.pdf

Also I saw that Texas is going into H-120 mode. That was posted by Scotta on KHOU.com. I'm not exactly sure what H-120 is. Does anybody?

[x-y-no]

I'm still trying to wrap my mind around how this storm could possibly move west as fast as forecast ...

Here's the initialization of the 18z GFS at 500mb:



Notice the 588 line passing through Jamaica and extending well south.

Here's 24 hours:



Note the ridge extending way south. Also note where it has the 500mb low and vort max over Haiti.

Now I'm not saying that Gustav will stall over Haiti. What I am saying is that I think the GFS (and hence the GFDL and HWRF) is moving it too fast to the west - straight into a mid-level ridge. A westward motion looks likely to me, but in my experience with this kind of situation it should be quite slow.

I'd love it if one of the pros would explain to me why I'm crazy here ... still trying to learn after all these years.

[TexWx]

Hour 120

[srainhoutx]

Not sure if this has been posted yet, but the State of Texas is now activated Emergency plans for a major hurricane.

ftp://ftp.txdps.state.tx.us/dem/sitrep/ ... 082608.pdf

Also I saw that Texas is going into H-120 mode. That was posted by Scotta on KHOU.com. I'm not exactly sure what H-120 is. Does anybody?

120 hours out before impact. This is very much standard for this type of threat. It helps all state govt agency to coordinate together. Purely a SOP thing right now.

[AJC3]

I'm still trying to wrap my mind around how this storm could possibly move west as fast as forecast ...

Here's the initialization of the 18z GFS at 500mb:

<snip>

Notice the 588 line passing through Jamaica and extending well south.

Here's 24 hours:

<snip>

Note the ridge extending way south. Also note where it has the 500mb low and vort max over Haiti.

Now I'm not saying that Gustav will stall over Haiti. What I am saying is that I think the GFS (and hence the GFDL and HWRF) is moving it too fast to the west - straight into a mid-level ridge. A westward motion looks likely to me, but in my experience with this kind of situation it should be quite slow.

I'd love it if one of the pros would explain to me why I'm crazy here ... still trying to learn after all these years.

One caveat I'd say to you is that the NCO stuff is awful coarse resolution. To really get a better feel for the ridge, you'd need to look at high res (10-20m contours) along with winds/streamlines. That would give you a better feel for the strength of the ridge to the north. The RAOBs at Jamaica the past couple days showed pretty stout deep layer easterlies...and I think you'll see Gus start to respond to this from here on out over the next few days by picking up some foreward speed with very little gain in latitude.

[cpdaman]

and it appears to be stuck over haiti and not making much progress

i mean could it have picked a worse latitude to stall right over the arm of high terrain and turn west to take the long route at the same time, it may be morning and this thing stuck on haiti

[Derek Ortt]

TWC just showed some heavy flooding in the eastern part of the DR. Likely much worse in Haiti

[LSU2001]

I'm still trying to wrap my mind around how this storm could possibly move west as fast as forecast ...

Here's the initialization of the 18z GFS at 500mb:



Notice the 588 line passing through Jamaica and extending well south.

Here's 24 hours:



Note the ridge extending way south. Also note where it has the 500mb low and vort max over Haiti.

Now I'm not saying that Gustav will stall over Haiti. What I am saying is that I think the GFS (and hence the GFDL and HWRF) is moving it too fast to the west - straight into a mid-level ridge. A westward motion looks likely to me, but in my experience with this kind of situation it should be quite slow.

I'd love it if one of the pros would explain to me why I'm crazy here ... still trying to learn after all these years.

Not a pro by any stretch of the imagination x-y-no but I think the GFS is up to its old tricks of dramatically overestimating the high pressure ridge and moving it too far west. IMHO, all of the models detect an expected weakness to develop somewhere over the GC states and a north or northwest turn shows in the models. It seems like always we will be up late over the next week waiting for the "expected north turn".
JMHO,
Tim

PS. I too can't wait for the pros to answer your post.

[cycloneye]

TWC just showed some heavy flooding in the eastern part of the DR. Likely much worse in Haiti

Sad to say that we will see news that not will be good from Hispanola.

[Sabanic]

UPDATED
NATIONAL WEATHER SERVICE MOBILE AL
636 PM CDT TUE AUG 26 2008


NOW THE NEXT ITEM AND THAT IS HURRICANE GUSTAV. GUSTAV WAS POSITIONED
WEST OF PORT-AU-PRINCE ON THE HAITI COAST. THE LATEST 21Z FORECAST
BY THE NATIONAL HURRICANE CENTER IS FOR GUSTAV TO SOON ENCOUNTER A
MID LEVEL RIDGE FROM THE EAST GULF ACROSS FLORIDA AND THE BAHAMAS.
THIS IMPARTS A WESTWARD TURN...TAKING GUSTAV ACROSS THE SOUTHERN
PORTIONS OF THE WINDWARD PASSAGE TONIGHT AND WEDNESDAY. GUSTAV
CONTINUES WESTWARD...SOUTH OF CUBA THURSDAY AND FRIDAY...THEN MOVING
UP ACROSS THE WESTERN TIP OF CUBA/OR THROUGH THE YUCATAN CHANNEL
SATURDAY. THE NEXT POSITON...THE CENTRAL GULF SUNDAY. THERE IS A
POTENTIAL FOR A MAJOR HURRICANE INTO THE GULF THIS LABOR DAY
WEEKEND. ALL INTERESTS ARE URGED TO STAY TUNED TO THE VERY LATEST BY
THE NATIONAL HURRICANE CENTER. /10

[ConvergenceZone]

I'm still trying to wrap my mind around how this storm could possibly move west as fast as forecast ...

Here's the initialization of the 18z GFS at 500mb:

<snip>

Notice the 588 line passing through Jamaica and extending well south.

Here's 24 hours:

<snip>

Note the ridge extending way south. Also note where it has the 500mb low and vort max over Haiti.

Now I'm not saying that Gustav will stall over Haiti. What I am saying is that I think the GFS (and hence the GFDL and HWRF) is moving it too fast to the west - straight into a mid-level ridge. A westward motion looks likely to me, but in my experience with this kind of situation it should be quite slow.

I'd love it if one of the pros would explain to me why I'm crazy here ... still trying to learn after all these years.

One caveat I'd say to you is that the NCO stuff is awful coarse resolution. To really get a better feel for the ridge, you'd need to look at high res (10-20m contours) along with winds/streamlines. That would give you a better feel for the strength of the ridge to the north. The RAOBs at Jamaica the past couple days showed pretty stout deep layer easterlies...and I think you'll see Gus start to respond to this from here on out over the next few days by picking up some foreward speed with very little gain in latitude.

and isn't this exactly what the NHC said this is going to do?? turn northwest, then west, then back northwest as it rides the high side of the high pressure ridge?....I think your forecast is right in line with the NHC

[x-y-no]

One caveat I'd say to you is that the NCO stuff is awful coarse resolution. To really get a better feel for the ridge, you'd need to look at high res (10-20m contours) along with winds/streamlines. That would give you a better feel for the strength of the ridge to the north. The RAOBs at Jamaica the past couple days showed pretty stout deep layer easterlies...and I think you'll see Gus start to respond to this from here on out over the next few days by picking up some foreward speed with very little gain in latitude.

I do look at the fine resolution, I just didn't want to waste the bandwidth posting them when the coarse illustrated my point adequately.

The 12Z sounding in Kingston has NE wind at a 500mb height of 5810m. I'm awaiting posting of the 0z sounding now. That'll tell us if the GFS initialization is way off or not.

[x-y-no]

and isn't this exactly what the NHC said this is going to do?? turn northwest, then west, then back northwest as it rides the high side of the high pressure ridge?....I think your forecast is right in line with the NHC

NHC has it south of Cuba in 16 hours, north of the western tip of Jamaica in 40 hours. I don't see it moving that fast if the ridging really is as depicted.

EDIT: that should be 18 and 42 hours.

[deltadog03]

I'm still trying to wrap my mind around how this storm could possibly move west as fast as forecast ...

Here's the initialization of the 18z GFS at 500mb:



Notice the 588 line passing through Jamaica and extending well south.

Here's 24 hours:



Note the ridge extending way south. Also note where it has the 500mb low and vort max over Haiti.

Now I'm not saying that Gustav will stall over Haiti. What I am saying is that I think the GFS (and hence the GFDL and HWRF) is moving it too fast to the west - straight into a mid-level ridge. A westward motion looks likely to me, but in my experience with this kind of situation it should be quite slow.

I'd love it if one of the pros would explain to me why I'm crazy here ... still trying to learn after all these years.

I would agree with you...I think its blocked it for now as well. I still see some slooooooow movement, but your right...good call!

[SWFLA_CANE]

I'm still trying to wrap my mind around how this storm could possibly move west as fast as forecast ...

Here's the initialization of the 18z GFS at 500mb:



Notice the 588 line passing through Jamaica and extending well south.

Here's 24 hours:



Note the ridge extending way south. Also note where it has the 500mb low and vort max over Haiti.

Now I'm not saying that Gustav will stall over Haiti. What I am saying is that I think the GFS (and hence the GFDL and HWRF) is moving it too fast to the west - straight into a mid-level ridge. A westward motion looks likely to me, but in my experience with this kind of situation it should be quite slow.

I'd love it if one of the pros would explain to me why I'm crazy here ... still trying to learn after all these years.

I would agree with you...I think its blocked it for now as well. I still see some slooooooow movement, but your right...good call!

Now if this is the case, what will the slow motion due to change the over all track?

[AJC3]

One caveat I'd say to you is that the NCO stuff is awful coarse resolution. To really get a better feel for the ridge, you'd need to look at high res (10-20m contours) along with winds/streamlines. That would give you a better feel for the strength of the ridge to the north. The RAOBs at Jamaica the past couple days showed pretty stout deep layer easterlies...and I think you'll see Gus start to respond to this from here on out over the next few days by picking up some foreward speed with very little gain in latitude.

I do look at the fine resolution, I just didn't want to waste the bandwidth posting them when the coarse illustrated my point adequately.

The 12Z sounding in Kingston has NE wind at a 500mb height of 5810m. I'm awaiting posting of the 0z sounding now. That'll tell us if the GFS initialization is way off or not.

Obviously, the NE mean layer wind flow at Kingston is not typical of the environmental wind that Gus is encountering -- it's the outer fringes of Gus himself. The fact that the H50 heights at Kingston aren't all that high isn't a big deal.The ridge axis and thus the higher heights are much farther north. If the heights there are in fact running lower than the GFS init panels, then they're probably being tweaked upward before being fed into the models. Perhaps the might run a little low there...I'm not sure.

Gimme a few and I'll fish out the RAOBs from Kingston from the past few days.

BTW...the system is not blocked at all. Radar shows it moving steadily due westward. Give it time and it should pick up some foreward speed.

[deltadog03]

I guess I shouldn't use blocked....I would say a temperary reduction in forward speed?? lol

[x-y-no]

OK, it makes sense that the NE wind at 12Z is the outer fringes of Gustav - I'll buy that.

No need to dig - I've looked at them over the last couple of days. The interesting thing wll be to see if the 0z sounding tonight has a substantially higher height. If not, the GFS initialization is just wrong at that level.

[dwg71]

not an eye, more of just ragged appearance, imo