LRandyB's Tropical Weather Discussion

Tropical Discussion Tue Sept 26th 9:00AM CDT

By: LRandyB, 1:51 PM GMT on September 26, 2006

Good morning!

It’s a beautiful day in the deep south! I hope everyone is enjoying their day! The tropics are getting a bit more active but not by much!

In the Gulf and Caribbean….

A cold front extends from the Atlantic Ocean southwest across central Florida and across the Gulf into northern Mexico. Cooler, dryer air has filtered in behind this front and dominates most of the southeast and south central US. An upper level ridge lies over the frontal boundary extending from a high pressure center in central Mexico. This ridge is helping to enhance some thunderstorm activity along the frontal boundary. The southern end of the front has gone pretty much stationary over the last 12 hours in the central Gulf.

Ridging aloft also covers the central Caribbean helping to enhance some convection with an easterly wave just southwest of Jamaica. Between this ridge and the one in the central Gulf is an induced trough. The trough axis is fairly weak and dry and is anchored on a barely visible low just off Belize. Another upper low is a bit more visible on WV loops just northeast of the southern Bahamas. But even this low has shown evidence of filling as the Atlantic ridge builds into the region. Another easterly wave is in the extreme eastern Caribbean. There is some scattered shower and thunderstorm activity with this wave as it moves west. We may see a bit more activity as it moves under the influence of the upper level ridging in the central Caribbean.

In the Atlantic….

A strong tropical wave near 23N 49W is moving WNW this morning. This is Invest AL96 that the models are tracking. The convection has gotten better organized and closer to the center of low level circulation this morning though the convection is still east and northeast of the center as a result of SW shear being created by a trough just west of the system centered near 26N 56W. The low level trough axis of the easterly wave is plainly visible on VIS images extending SSW from the low level circulation center. NHC feels this system has the potential to develop over the next 24 hours. I’d be surprised to see any significant development in this low. The trough and upper level low west of it isn’t showing signs of going away though it is tracking slowly west with AL96 so the shear most likely won’t relax anytime too soon. Also on visible images, AL96 is at the NW leading edge of a Saharan Air Layer the extends SE into the tropical Atlantic. And even the WV lops show the system surrounded by dry air. So if development is to occur, it’ll have an uphill battle. So far the models recurve the system harmlessly in the open Atlantic achieving little more than TS strength. That seems a reasonable forecast to me.

Another wave to watch is near 10N 34W. Convection has been on the rise with this area. There are no signs of organization as yet and it still lies pretty much within the ITCZ but it bears watching.

And lastly, a new wave is coming off the African coast this morning with a fair amount of spin. At least one of the models want to develop this wave but that model pulls the system immediately north into the Azores. So we’ll wait and see what this does, if anything.

I hope the weather is beautiful where you are and you get a chance to get out even for just a bit today and enjoy it!

Randy


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Tropical Discussion Sat Sept 23rd 1100am CDT

By: LRandyB, 4:26 PM GMT on September 23, 2006

Good morning!! The tropics seem to be settling down a bit. Let’s hope it stays that way! Let’s have a bit of weather trivia today before we get to the tropics!

Today is the Autumnal Equinox or the first day of fall! What exactly is the Autumnal Equinox.? Well, the earth tilts on it’s axis at an angle of 23.5 degrees. When the suns rays strike the earth, the angle at which they strike it depends on where in it’s orbit around the sun the earth is. In the months of November through February the north pole is tilted away from the sun and the south pole is tilted toward the sun. The suns rays strike the southern hemisphere more directly resulting in greater heating. They strike the northern hemisphere at a sharper angle resulting in less heating. So in the months of November through February we experience summer in the southern hemisphere and winter in the northern hemisphere. In the months of April through August, the process is just the opposite with the north pole tilted toward the sun and the south pole tilted away from the sun. So we have summer in the northern hemisphere and winter in the southern hemisphere.

On mid-summers day (in the northern hemisphere) when the suns rays are striking the earth directly at the farthest northern point (23.5N latitude) we actually call this the first day of summer or the Summer Solstice. It usually falls on the 21st of June. This is the longest day of the year in the northern hemisphere. When the suns rays strike the earth at it’s southern most point (23.5S latitude), we call this the Winter Solstice or the first day of winter in the northern hemisphere and it falls usually on December 21st. This is the shortest day of the year in the northern hemisphere. In between these two dates comes the day when the day and night are equal lengths in both the northern and southern hemisphere. We call these dates the Autumnal Equinox and the Vernal (or Spring) Equinox or the first day of fall and the first day of spring respectively in the northern hemisphere. The Autumnal Equinox usually occurs on Sept 23rd and the Vernal Equinox usually occurs on 21st of March.

On the earths surface, we mark the three latitude lines that help us track the progression of the suns overhead position on the globe. They are the Equator (0 degrees latitude) , the Tropic of Cancer (23.5 N), and the Tropic of Capricorn (23.5S). On the day of the summer solstice (in the northern hemisphere) the sun is directly overhead the Tropic of Cancer. On the day of the winter solstice, it’s directly over the Tropic of Capricorn. At the mid points between the two (the Autumnal and Vernal Equinox’s) the sun is directly over the Equator.

These dates change over thousands of years however because the earth also happens to wobble on it’s axis. So in a few thousands years, the seasons will reverse themselves on the earth!

Now on to the tropics!!!!

In the Gulf and Caribbean…..

The current WV and IR loops look more like a fall or winter pattern here than the peak of Hurricane Season! Lots of dry air dominates over most of this region. There is an upper level low over the south central Gulf tracking slowly NNW. There are a few scattered showers associated with this low. A weak easterly wave is passing through the central Windward Islands today.

In the Atlantic….

A rather strong ridge of high pressure is building into the central and western Atlantic today. WV loops show it building both east and west from a center near 28N 68W. The axis of this ridge is also pushing south and orienting itself more E-W over time. A weak upper level low is near 22N 63W tracking west on the flow around the ridge. This low is actually the southern end of a trough that pushed across the Atlantic picking up Helene. This low got cut off and left behind. It is weakening with time as it tracks west.

The next possible significant tropical feature we have to watch is a wave along 40W. The axis of this wave extends from about 10N to nearly 25N. NHC says there is a low pressure center near 12N. The convection in the northern extent of this wave is being sheared by the flow from the upper level low and trough to the NW of it. But the low center and southern extent of the wave are far enough south to avoid that shear. This wave is being tracked by the models as AL96. Right now the models all indicate that this wave will pull NW in the flow around that upper low and trough that lies to the west of it.

That’s about it. We’ll keep an eye on AL96 and see where it goes!

Please enjoy your first day of fall!!!

Randy






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HAPPY BIRTHDAY RaysFan70!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

By: LRandyB, 10:47 PM GMT on September 22, 2006

Sorry Rays that I didn't get this up earlier! I flew this morning!!!

And of course, I can't play favorites to Emmy! :-)

Happy Birthday!

Updated: 11:24 PM GMT on September 22, 2006

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Tropical Discussion Thur Sept 21st 6:00am CDT

By: LRandyB, 11:33 AM GMT on September 21, 2006

Good morning! This shouldn’t be too long a discussion. There isn’t a lot happening in the tropics this morning!

In the Gulf and Caribbean…..

It’s a challenge to find any features on satellite to talk about here. The trailing end of the front that pushed off the east coast earlier this week is oriented E-W over the central Gulf and is stalled out. High pressure centered just off the central TX coast is pushing east and helping to weaken that fading frontal boundary. Very dry and cooler air has settled into the southeast US behind that last front but as that high moves east, more seasonal warm and humid air will filter back into the region.

An upper level low can be found in the western Caribbean. This is a cutoff remnant of a fairly deep trough that extended down into the central Caribbean earlier this week. That strong cold front pushed out the trough and left the southern extent of the trough to cut off into the low that is now drifting west. There’s no real weather associated with this but there is an increase in mid-level moisture around it.

Lastly for this area, a fairly strong ridge of high pressure is building into the eastern Caribbean and western Atlantic today.

In the Atlantic…..

It gets a bit more interesting here. Helene is currently near 28N 56W and is being pulled ENE ahead of that cold front off the east coast. She won’t be bothering anyone.

In the central Atlantic, a fairly deep trough extends south to near 18N 43W and is anchored by an upper level low near 23N 38W. A ridge if high pressure is building in east of that trough and looks to be eroding the trough and nudging the upper level low northward.

A strong tropical wave is located just west of the Cape Verde Islands. This wave came off Africa a couple of days ago and looked pretty impressive at the time. NHC mentions it in their tropical weather outlook this morning but at the moment, this wave appears to be getting pulled to the north by that trough sitting just west of it. A couple of the models try to develop this wave and move it NW and then west as the ridge builds back in from the east Atlantic. They also develop a new wave off Africa over the next 48 hours or so. While not all the models agree on the development of these waves, all do agree on building that ridge back in across the Atlantic quite strong. So any waves that do develop off Africa are likely to move west.

Have a great day today!!!


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Tropical Discussion Tue Sept 19th 11:00am CDT

By: LRandyB, 3:57 PM GMT on September 19, 2006

Good morning folks! Not a lot of change in the tropics this morning. It’s almost looking like fall on the satellite images. Deep strong fronts pushing through the southeastern US and deep strong troughs affecting the tropics even around Africa. Kinda strange!

In the Gulf and Caribbean….

A strong cold front has pushed into the central Gulf states this morning bringing dryer cooler air into the region. The upper level trough extends all the way down into northern Mexico. It looks like the southern end of the front is stalling off Brownsville TX. We might see a wave develop there and work up the front later this week. A ridge has developed ahead of this upper trough and is helping to enhance some convection in the Bay of Campeche but nothing serious there. An upper level low located midway between Bermuda and the east coast has an associated trough that extends south into the central Bahamas. There isn’t much weather with this trough but it is serving as an effective block for any easterly waves that might wander into this area. The only area of interest I see in the Caribbean is a weak area of persistent convection south of Jamaica off the northern coast of South America. There is no real motion to this convection and any motion it may decide to take will take it into areas bad for tropical development so it most likely won’t cause any problems for anyone.

In the Atlantic….

Gordon is now caught up in the westerlies and is racing along 38N toward Europe. It’ll be a powerful maritime system to contend with when it gets there.

Helene, now out from under the influence of Gordon, has picked up a WNW (almost due west) track along 24.5N. This track is expected to continue for the next 24-36 hours before the upper low and strong trough that constitutes the frontal system pushing through the eastern US moves off the east coast and begins to pull Helene northward. At the moment, the ridge axis ahead of Helene lies near 63W. West of that axis is where the winds shift to a southerly direction. That axis may get pushed a bit east by the approaching trough so NHC doesn’t expect Helene to get past 60W. In any case, she isn’t expected to impact anyone in the US or Bermuda before recurving into the Atlantic.

In the eastern Atlantic, an upper level low near 22N 34W and a trough associated with it extending south to almost 15N has done an incredible job of blocking waves coming off the African coast. The last couple of waves to come off the coast of Africa have actually been pulled due north right off the coast and turned NE into northern Africa. The trough is weakening now near 15N so the ITCZ is developing a bit more convection today. There is evidence on WV loops of an easterly wave passing by the southern extent of that trough near 10N 37W that has some persistent convection with it. We’ll watch the track of this wave as it moves into the central Atlantic.

That’s the update for today! Have a great day!

Randy

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HAPPY BIRTHDAY EMMYROSE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

By: LRandyB, 1:07 PM GMT on September 19, 2006

Good morning Emmy.. and everyone!

Yes I know.. this is a tropical discussion blog.. just couldn't resist the temptation to wish Emmy a Happy Birthday today!

Randy

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Tropical Discussion Sun Sept 17th 10:30pm CDT

By: LRandyB, 3:42 AM GMT on September 18, 2006

Good evening folks! Things are a bit calmer but not by much! We still have Gordon and Helene in the Atlantic. Lane went ashore in Mexico. There are a couple of waves coming off Africa over the next 24 hours but nothing that looks to be a problem. The Gulf and Caribbean are quiet as well. Since Gordon is headed off into the northern Atlantic, let's talk a bit about Helene.

Helene at the moment is tracking NW. In fact over the last 3 or 4 hours, I'd have to say it's tracking almost due north. This track is being caused by a weakness in the ridge north of Helene created by Gordon. Current forecast reasoning has Gordon accelerating pretty quick out of the picture over the next 8-12 hours. There after, the ridge builds back in allowing Helene to resume a west or WNW track for a few days before the next trough begins to pick it up. However, this is where the models diverge significantly. You can read the NHC discussion this evening to catch the details of that. What the models are basically trying to forecast is the amplitude of the next two deep long wave troughs crossing the US this week. The first is currently anchored on a low in eastern ND and the trough extends SSW into the 4-corners region. At the 300mb level where the jet is, the jet max and 500mb vorticity max is already working their way out of the base of the trough. And there is no significant jet or vorticity max working its way into the trough on the west side. What that means is that low will begin to kick out to the ENE and the trough associated with it will not be able to dig any further south. However, as this trough pushes east, its influence does extend as far south as N FL, producing a southerly flow aloft in that area. But the NGM model shows the trough pulling north with the low as it moves over the ocean. What that means is that the first trough will most likely not extend far enough south to pick up Helene. But most of the global models agree with that scenario. So the real question is, will the next trough pick it up. Once again, looking at the NGM, it's hard at this point to say. The next trough is currently anchored on a low in the Gulf of Alaska and the trough extends south into the Pacific Ocean. Over the next 48 hours. This low and its associated trough are expected to push into the Pacific Northwest. The NGM shows an induced ridge building between the two troughs in the central plains. This induced ridge is aided by a strong high pressure ridge that is expected to develop over Mexico and the western Gulf of Mexico. This looks, on the models, to have the effect of limiting the extent to which the next trough is able to dig south. And in fact, the next trough doesn't look like it will make it as far south as the first trough does.

What does all this mean? Well, it basically means it's still a guess as to whether or not Helene will be picked up by either trough. The global models have been shifting further and further west. I said in my discussion late last week that I expected this to happen but I also didn't expect Helene to make it as far north as she has gotten so far.

So we'll have to sit back and see how the scenario unfolds. At the moment, at the very least, Bermuda will have to keep their eye on this one. I fully expect the Plan of the Day tomorrow to send us back to the Caribbean Tuesday to start flying Helene in anticipation of the threat to Bermuda.

Have a great evening!

Randy

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Hurricane Lane 16 Sept

By: LRandyB, 1:23 AM GMT on September 17, 2006

We flew a 9 hour mission and took Lane ashore in western Mexico. It was a bumpy ride but any storm we fly that is interacting with terrain is a rough ride.

We made one fix and a radar fix. On the forst fix the sonde read 955mb on the eye drop. On the eyewall drop inbound, the sonde registered 108kts (123 mph) on the surface. That's a solid Cat 3.

I took a few shots but mostly of the radar and crew. There wasn't much to see out the window.

Updated: 2:04 AM GMT on September 17, 2006

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Tropical Discussion Fri Sept 15th 10AM CDT

By: LRandyB, 2:58 PM GMT on September 15, 2006

Good morning everyone! The tropics are rather busy these days for us. Between tasking for systems in the Atlantic basin and tasking for Pacific storms, we've been on the go here! But let me jump into the discussion.

In the Gulf and Caribbean.....

There is a veritable plethora (been looking for an excuse to use that word) of troughs and ridges in this area. Let me see if I can break them down for you.
First off is a trough that is actually an extension of a frontal boundary that extends from New England out into the Atlantic, south down the eastern seaboard, and then southwest across the northern peninsula of FL, and then west across the Gulf to just off the coast of South TX. The southern end of this boundary has weakened to the point of not really producing any weather today but showers and thunderstorms do persist along the boundary in the Atlantic.

South of this trough is a ridge axis that originates with TS Lane in the Pacific just off the coast of Mexico and extends east across Mexico, across the Yucatan into the FL Straits and on into the Atlantic. Upper level difluence with this ridge is helping to enhance some of the convection ahead of the front in the Atlantic.

Ahead if this ridge is another deep trough that extends from the Atlantic across the southern Bahamas to just off the east tip of Cuba. There's evidence on WV loops of an upper level low circulation at the base of this trough in the southern Bahamas.

There is a weak upper level ridge that extends from southern Central America out into the central Caribbean. This ridge has been enhancing a lot of convection over the south central Caribbean just north of Panama.

Lastly, and most prominently, a strong ridge of high pressure extends from the tropical Atlantic westward into the eastern Caribbean. This ridge is building steadily west and bringing with it a very dry airmass. An easterly wave at the leading edge of this dry air has been producing showers and thunderstorms as it crosses the central Windward Islands.

We're getting back into the part of the season where most of our significant tropical development will occur in the Caribbean and the Gulf so the only tropical activity I see that might warrant watching is the convection in the southern Caribbean under that weak ridge off Panama.

In the Atlantic.....

Of course we have Gordon headed out into the open waters of the Atlantic. Over the last few hours, the eye of Gordon, which was so well defined yesterday, has started to fall apart and the storm in general is losing a lot of energy. It's also stalled out somewhat and has begun perhaps a slow north-northeast crawl. With the approaching front west of Gordon, I would expect to see this storm get rapidly picked up in the SW flow and begin it's transition to an extra-tropical system within the next 36-48 hours.

Next we have Tropical Storm Helene in the central Atlantic. While Helene isn't looking too robust at the moment, she is a healthy storm. Outflow is good in pretty much all directions and there is a fair amount of deep convection in the southern half of the storm. However, over the last couple of hours, the convection has begun wrapping around the eastern side of the storm as well. General motion of the storm is due west. The models and the official NHC forecast keeps Helene on a WNW track turning a bit more toward the NW and north later in the period. I'm not buying that forecast at the moment because, as I mentioned in the Caribbean discussion, the ridge in the Atlantic that is driving Helene at the moment is actually building west over time. This would tend to keep Helene on a WNW track longer than the current forecast calls. One factor that may offset that somewhat however is that Helene doesn't appear to be in the outer periphery of the steering flow around the ridge but actually closer to the ridge axis. It wouldn't take much of a northward drift to put Helene on the north side of that axis and more into the more SW flow. But at the moment, based on the orientation of the ridge axis and the rate at which it is building, I think Helene will most likely keep to it's WNW track longer than the forecast is calling for. As for intensity, the biggest hindering factor for Helene right now is that it is embedded in a very dry airmass. But upper level winds and SSTs are conducive to strengthening. If she doesn't take a more northerly track soon, we'll be heading back to the Caribbean to fly her by Monday most likely.

Behind Helene, another strong wave has just come off the coast of Africa. But between the dry air in the Atlantic right now and the outflow from Helene, I don't know that this wave will have the opportunity to develop.

That's it for now. We are currently flying TS Lane. I am scheduled to fly it as a hurricane tomorrow. I'll take my camera as always!

Have a great weekend!!!!

Randy

Updated: 2:59 PM GMT on September 15, 2006

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Tropical Discussion Tues Sept 12th 10:00am CDT

By: LRandyB, 3:04 PM GMT on September 12, 2006

Good morning weather fans!

Well, Florence is headed out to the North Atlantic to bother the shipping lanes. And Gordon is looking to do the same thing even further east. NHC canceled the tasking for today into Gordon and we have no follow on tasking tomorrow so we’ll be heading home tomorrow. Now let’s look and see what we have to look at until the next storm comes in range!

In the Gulf and Caribbean…..

Things are about as quiet as they can be in this region of the tropics which is not too uncommon this time of year. A large area of high pressure aloft covers most of the Gulf and the Caribbean. A trough of low pressure is evident on WV loops from northern Central America into the Yucatan and an upper level low has developed in the circulation of the trough just off the west tip of the Yucatan. And a trough of low pressure, the trough that picked up Florence and is expected to pick up Gordon, is pushing all the way into the eastern Caribbean and is eroding the high pressure ridge in this area. In fact it’s doing such a good job, that here in St Croix where they would normally have a good strong easterly flow to push off any developing thunderstorms, the flow is so weak right now due to the approaching trough opposing the low level easterly flow, that the daytime thunderstorms are not going anywhere. They are developing and dumping on the island. But nothing if a tropical nature seems to be lurking in this area of the tropics.

In the western Atlantic….

Hurricane Florence is well north of Bermuda now making it’s way NE into the open North Atlantic. We don’t expect her to be a threat to anyone other than a few ships. TS Gordon is already making it’s northerly turn off the northern Windward Islands and should continue on out to sea without even bothering Bermuda. The rest of the western Atlantic is pretty quiet.

In the eastern Atlantic….

NHC just started issuing advisories in TD#8 just off the coast of Africa. This feature does indeed look quite impressive. Most systems come off the coast and immediately lose their convection. This one blew up after it got over water. The models build it into a hurricane within a couple of days. The real big issue is the track. The models aren’t in good agreement with the long range track, varying from a more westerly track to a recurving track over the central Atlantic. But at the moment, I wouldn’t buy into any of them too quick. It’s pretty unusually for a system to develop so quick off the African coast. The models haven’t had the chance to pick on it yet and there isn’t a lot of data in that area for them to work with. NHC reports that there is a DC-8 there dropping sondes for a experiment so hopefully the models will have more to work with than usual this far east. The next run of the models should have a better handle on this system.

But in any case, we could be back here in the Caribbean this weekend.

Have a great day and I’ll post more tonight!

Randy

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Hurricane Florence Mon Sept 11th 10:30am CDT

By: LRandyB, 4:39 PM GMT on September 11, 2006

Good morning folks!

Well we made back unscathed from Florence yet again! ;-) Actually it wasn't that challenging a storm to fly. We made 4 passes through the center. On each pass the sondes we launched showed a 1MB fall in pressure from 978 on the first pass to 975 on the last pass. But the internal core tempurature fell 4 degrees in the same time frame. And the highest winds we encountered (near 70kts) were fairly far removed from the center and got farther from the center on each pass. The storm had a partial eyewall around the north side of the eye on the first pass but that fell apart pretty quick on subsequent passes. So it looks as if Flo is making it's transistion to extratropical.

Only the last pass through the eye was in daylight so I didn't have many good picture opportunities but I took a few that you'll see below.

Now I am off to bed for a few hours. I'll post a full update this evening to include TD#7.

And please take a moment to pause and reflect today on the lives lost 5 years ago today. At this time 5 years ago today I was dodging dust clouds in lower Manhattan just a few blocks from the WTC Complex. But I was lucky. It is a day I'll never forget.

Thanks,

Randy

Updated: 4:41 PM GMT on September 11, 2006

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Tropical Discussion Sun Sept 10th 5:00pm CDT

By: LRandyB, 10:04 PM GMT on September 10, 2006

Good afternoon everyone! Well, I’ll be headed out in a few hours to fly Hurricane Florence. I flew the first flight into her on Friday night and it looks like my crew will fly the last flight into her tonight. I’ll post pictures and let you know what we found when I get back from that flight. In the meantime, let’s talk about Florence and anything else in the tropics.

In the Gulf and Caribbean….

Large scale broad upper level ridging is occurring over the entire Gulf and Caribbean. This is being aided by the large upper level high and associated ridging being created by Florence over the western Atlantic as well as an upper level high over northern Mexico. A ridge from the high in Mexico extends east across the northern Gulf and is helping to enhance convection there but the activity is staying offshore. Other than that, the Gulf and Caribbean are very quiet.

In the western Atlantic…..

Well the big story of the day of course is Hurricane Florence. One of our AF planes is in the storm now and will be there until about 8pm EDT. My flight is expected to be there by about 1:00 or 1:30am EDT. By then, it should be very near Bermuda and if it follows the current forecast, may be a Cat 2 storm by then. Current satellite shows that it may be moving due north or maybe even a little east of north. The satellite signature is looking a little ragged in the last few images as well. The trough west of Florence is pushing off the east coast at this hour and should be impeding Florence’s pattern pretty soon. You can already see evidence of the upper level outflow extending to north of Flo being carried quickly off to the NE. As Flo moves just a bit further north and the trough moves closer, you’ll begin to see Flo do the same thing. There is also some indication on WV loops of dry air beginning to entrain on the west side of the storm as well. The center in the last couple of hours has become less defined on satellite. Tonight’s flight will help determine the health of the system as it near extratropical transition.

Elsewhere in the western Atlantic, an area of convection has developed in the wake of Florence near 19N 54W. NHC has mentioned this area in the TWO for the last day or two but they don’t seem too concerned about it at the moment. While the convection has persisted and NHC says there is a low associated with it, it’s also being fed by an upper level col over the convection. The flow is stronger out of the col than the flow entering the col so the overall flow is divergent overhead. So it is possible if Flo gets far enough away, the col will collapse and without that support, the convection will die. Hard to tell at this point. One of the biggest indicators of this is that the area is moving a bit south of due west rather than west or WNW as you would expect here. That may be because of the shifting in that upper level flow. I was surprised when NHC did not task us to fly that area and it wouldn’t surprise me to see the POD changed or for them to ask for a resources permitting flight tomorrow. We’ll have to watch this are for any indication that it can sustain itself.

The rest of the Atlantic is pretty quiet. Even the ITCZ is not as active as it has been. A regular train of waves have been coming of Africa but none have amounted to anything and die off within 24 hours. Saharan Dust is evident in the Atlantic in visible images all the way out to nearly the Windward Islands south of 15N. And in the eastern Atlantic, mid-level flow around an mid-upper level low near 27N 35W is pulling the dust all the way up to near 30N. As we already know, that kills tropical development for all but the most robust systems.

I’ll post again in the morning when I get back from Florence!

Have a great Sunday evening!

Randy

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Tropical Discussion Sat Sept 9th 5:00am CDT

By: LRandyB, 10:08 AM GMT on September 09, 2006

Good morning folks! I just got back on the ground from our first flight into Florence. It was an uneventful flight and we found the storm to be pretty unimpressive. But during the time that we were in the storm it did show signs of increasing in intensity. We made two passes through the center. The first pass found the center about 83 miles southeast of where NHC thought it would be. That exemplifies why we fly these missions. The sondes I dropped reported a minimum pressure of 998MB on the first pass (at 12:04am EDT) and 993MB on the second pass (at 2:35am EDT). 5MB in 2 and a half hours is pretty respectable. Maximum flight level winds recorded were about 61 knots in the NE quad (as expected). General motion between the two fixes was about 300 degrees at 15kts. Radar presentation of the storm and overall structure was still pretty ragged.

The storm is still expected to turn north and northeast over the next 12-36 hours as it rounds the western edge of a ridge in the Atlantic. And with shear nearly gone, the storm has a small window of opportunity to gain some stregnth before the trough on the west coast catches it and starts to shear it as it pushes it north.

The pictures below we're taken during the flight this morning. Since it ws dark the whole flight I couldn't get any outside shots.

Updated: 10:09 AM GMT on September 09, 2006

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Tropical Discussion Fri Sept 8th 12:30pm CDT

By: LRandyB, 5:45 PM GMT on September 08, 2006

Good afternoon folks!

Well, we'll fly out this evening to TS Florence and see what she looks like. Looking at satellite, it's actually starting to look a bit more organized this afternoon. There is a bit more symmetry in the outflow pattern and the overall circulation looks better. It also appears that the low level center of circulation has moved into the convection. So strengthening is possible over the next 24 hours. Now we need to watch the upcoming interaction between Florence and the deep trough working it's way across the central US. Right now this trough has managed to push it's way all the way down the north central Gulf of Mexico. As this feature moves off the east coast, it should turn the overall deep layer winds to the SW in the western Atlantic, causing Florence to begin to make its NW and N turn and accelerate into the North Atlantic. At the moment, it looks like the only folks Florence may threaten is Bermuda and some shipping lanes. We'll see what the data looks like that we collect tonight.

Elsewhere, the Gulf and Caribbean are quiet other than the showers and thunderstorms associated with that front and upper trough pushing through the central Gulf states. In the Atlantic, there is a wave near 8N 38W that has been quite persistent. It's far enough south of Florence and the deep trough to be unaffected by them and has had some persistent convection with it for the last 24 hours. So I'll be watching that. Also a new wave just came off the African coast with some deep convection but we give it a day or two to see how, if at all, it develops.

I'll update tomorrow morning, hopefully with pictures if we manage to be in the storm during daylight.

Randy

Updated: 6:06 PM GMT on September 08, 2006

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Tropical Discussion Wed Sept 6th 9:30pm CDT

By: LRandyB, 3:08 AM GMT on September 07, 2006

Good evening folks! A quick update as there really is little happening other than TS Florence.

The thunderstorm activity we saw yesterday morning over SE FL kicked out as a wave along the frontal boundary that extended down the east coast and became a matter of concern for NHC this afternoon. They requested a resources permitting flight into that area off the GA coast and we sent a plane. For those who aren't familiar wih the term "resources permitting", let me explain. Normally, for storm tasking, our crews require a 12 hour crew rest period before they show up for a flight. That basically means that NHC needs to give us at least 12 hours notice on any tasking. In reality it needs to be a bit longer than that because we need time to assign and notify crew members of the tasking and put them into crew rest. If the tasking involves deploying to the Caribbean then we actually need a couple of days notice. So todays' possible tasking for Florence is for Friday. That gives us today to find and notify crews, and tomorrow to get there and put a crew into crew rest for a Friday morning flight. When NHC asks for a resources permitting flight, they are basically asking us if we have a crew already crew rested that could fly immediately into an area. Since we do generally fly local training flights on a daily basis for which the crews are expected to be crew rested, we can usually accomodate NHC. The flight into the suspect area did not find anything of concern and that area of convection is rapidy racing off to the NE into the Atlantic.

The upper level low NW of Florence has cut off and is tracking west ahead of Florence. So far it hasn't put enough distance there to relax the shear but instead, the wind field around Florence has become large enough and strong enough to begin to overcome some of that shear. So we're seeing an increase in convection near the center of Florence as well as a more symmetrical outflow pattern around the storm. This spells the beginning of intensification for the storm. The models are all in tight agreement over the track of this system. A trough of low pressure is expected to create a strong weakness in the ridge that is currently driving Florence WNW and allow a NW and then N turn of the storm by about the 72 hour point. As the upper level low west of Florence tracks west away from her, the shear will relax and allow for some strengthening of the storm. It is expected to make at least a Cat 3 by the 3-4 day point as well.

NHC gave us tasking for this system so we'll be sending planes and crews to the Caribbean tomorrow to fly Friday. I'll be on the first crew out and into the storm Friday morning. I'll take pictures and give an update on what we find when I get back.

In the meantime, I'll post an update tomorrow morning before we fly out!

Have a great night!

Randy

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Tropical Discussion Wed Sept 6th 6:00am CDT

By: LRandyB, 11:29 AM GMT on September 06, 2006

Good morning!

There's not much change this morning in the Gulf or Caribbean nor much happening there. So we'll jump right to the Atlantic where things are a bit busier.

There are four features that stand out on satellite this morning in the west and central Atlantic.

First, in order from west to east, is a weak upper level anti-cyclone that has developed over Haiti and the Dominican Republic. Flow around this high pressure center was helping to enhance some convection associated with an easterly wave yesterday but activity has diminished this morning.

The next feature is an upper level low developing near 23N 56W. This is a low that was forecasted by the models to develop at the tail end of the trough that is pushing through the central Atlantic. So far the models are on the money with this feature.

Next of ourse, is TS Florence located near 18N 50W. The upper level low to the west of it has been doing a good job of shearing the convection in TS Florence to the east of the low level center. And this morning that trend continues with a burst of deep convection occuring overnight around the east semicircle of the storm. The convection does seem to be trying to get closer to the center but it's not there yet. Until that happens NHC is unlikely to upgrade the winds on this system. The models drive Florence WNW for the next 3 or 4 days. Then a shortwave trough is expected to create a weakness in the ridge that is steering Florence and allow the storm to turn more NW. NHC is indicating, and so far the inialization of the models is showing, that the models are not doing a great job of handling that shortwave trough or it's impact on the ridge. So I wouldn't hold my breath on a turn just yet. But the models are all in amazing agreement on that turn! So we'll have to wait and see. As for intensity, the big deciding factor is the location of that upper level low to the west of Florence. As long as that low remains so close to Florence, the shear will not relax and Florence will not have a chance to intensify. The models are expecting that low to start to retrograde to the west and that should allow for some weakening of the shear over Florence.

The fourth feature we're seeing in the west and central Atlantic is a tropical wave just to the ESE of Florence. This wave had some potential to develop but has gotten too close to Florence to be able to do so. The wind field around Florence is actually quite large for an early stage tropical system and extends out to where this wave is in the upper levels. So I wouldn't expect to see this system develop unless it can put some distance between it and Florence.

In the east Atlantic, one wave has worked it's way off the coast of Africa and another is doing so today. Neither looks too impressive but the models have been developing a string of waves off Africa so we'll have to keep our eye on this area for developing waves.

That's it for this morning. Have a great day!!!

Randy

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Tropical Discussion Tue Sept 5th 1:00pm CDT

By: LRandyB, 6:22 PM GMT on September 05, 2006

Good afternoon folks! Sorry for the delay in getting the update out this morning. It's been a busy day catching up after the 3 day weekend!

Things are starting to get a bit busier in the tropics as we approach the statistical peak of the Hurricane Season. Before I talk about TS Florence, let's cover the rest of the tropics.

In The Gulf and Caribbean....

There's not a lot going on here but there are a couple of things we need to discuss. An upper level low shows up on water vapor loops in the south central Gulf. There's no real weather associated with this but the flow around this low is producing some difluence over south FL helping to enhance some thunderstorms there that look to have been kicked off by a combination of the diurnal sea breeze front and a weak easterly wave pushing through the area. Winds in SE FL are more southerly than usual resulting in the sea breeze developing closer to the SE coast than is usual. I'd expect to see these storms shift west during the day and die off toward the end of the day as the wave loses it's sea breeze help and day time heating over the land.

Another area to watch is a tropical wave in the eastern Caribbean. This wave has been traversing the west Atlantic and the Windward Islands for a few days now. NHC mentioned this wave late last week but at that time an upper level low in the western Caribbean was producing a large area of strong westerly shear. This week that low has subsided and the shear has relaxed. So overnight and into this morning the convection has increased significantly with this wave. There's no real organization to this wave but it bears watching.

In the Atlantic......

A deep trough is passing the central North Atlantic today. The models forecasted the southern end of this trough to stall or shear off into an upper level low and water vapor images show that process seems to be happening. An upper level low is becoming evident near 25N 55W. This low is expected to start tracking west.

TD#6 was upgraded this morning to TS Florence by NHC. Florence has had a good satellite signature over the course of the day today even though it didn’t look to healthy first thing this morning. On current visible images, I would put the center of low level circulation near 17N 48W. Movement is hard to discern because the center of circulation only recently consolidated into one defined center. But current motion is slow and might be NNW. The SW shear over the system has begun to relax as the upper low develops at the tail end of the trough passing by to the north of Florence. This should help to induce an upper level ridge over Florence and as the trough passes by, ridging is expected to develop north of the system. Ridging overhead will help the storm to intensify and ridging to the north should allow for a more easterly steering flow. Evidence of the shear relaxing is seen in the latest loops as convection is starting to develop on the west side of the center of low level circulation.

So, with the ridge building in north of Florence creating a easterly flow, the models keep the system on a WNW track. Toward the end of the forecast period most of the models want to start a NW turn as a weakness is expected to appear in the ridge. NHC mentions that they aren’t sure that the models are handling that weakness properly. It’s not uncommon for the models to be too aggressive and too fast with these types of mid-latitude features. So we’ll have to wait a couple of days to see what happens as the models progress.

Another wave lies a few hundred miles east of Florence. NHC says this one has a chance to develop but as Florence seems to slow a bit, I think this wave is going to get a bit too close. Since Florence seems to be getting it’s act together today, I think the upper level shear from the outflow around Florence will end up shearing this new wave and preventing development. It should be noted however, that the models do try to develop that wave as well.

The only other feature of interest in the Atlantic is a new wave coming off the African coast near 5N. We’ll have to watch this wave. None of the models are really picking up on this wave so it may amount to nothing.

Have a great afternoon! I’ll update again this evening.

Randy

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Tropical Discussion Sun Sept 3rd 6:00pm CDT

By: LRandyB, 11:31 PM GMT on September 03, 2006

Good evening folks! This would normally be the end of the weekend but we get one extra day this week!!!!!

NHC initiated advisories on Tropical Depression #6. And it is indeed an impressive looking system. Right now it's located at 16N 40W based on WV and IR images. It seems to have consolidated it's convection into one rotation now but because it has just finished that consolidation, it's hard to tell exactly where the center is going. The appearance is that it's moving NNW but that could just be the way the convection has settled. We'll have to wait a couple of more hours to see where it's going. As for the future of the system, right now it's sitting under fairly good upper level conditions to develop. There is some SW shear to the west of it being created by the approaching trough but the trough axis is already nearly even with the center of TD#6 so I'd expect it's influence to only last another 18 hours or so. Then a ridge builds in behind the trough which should push the storm back on a westward track. This is the general story being told by the models right now but they vary on when the turn to the west will occur and how much influence the trough will have on the position and track of TD#6. At the moment I lean toward believing that the distance between the trough and TD#6 is great enough to minimize the influence of the trough. So we'll have to wait until tomorrow to see what happens!

Elsewhere, the tropics are quiet although the GFS model develops another system on the heels of TD#6. We'll see if that pans out.

I'll post again tomorrow!

Randy

Updated: 7:24 PM GMT on September 04, 2006

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Tropical Discussion Sat Sept 2nd 9:00am CDT

By: LRandyB, 2:16 PM GMT on September 02, 2006

Good morning weather fans!

I hope everyone has some fun planned for their 3 day weekend! The tropics are relatively quite but we do have a couple of things to talk about!

In the Gulf and Caribbean…

A trough of low pressure dominates the western Gulf and has managed to push a slot of dry air all the way down to southern Mexico. The southern half of that dry slot is gradually being squeezed out by moist ridges on either side of it. But it’s still going to do a pretty good job of keeping any weather from developing along the western Gulf Coast today.

Just north of the southern Bahamas an upper level low is dominating the flow around much of that region including the western half of the Caribbean. Between that upper low and the tough in the western Gulf, an induced ridge extends from northern Central America up over the Yucatan and across central FL. This ridge is pulling tropical moisture up into the eastern half of the Gulf. The flow around the upper low is producing a strong westerly flow across the western and southern Caribbean. This flow is producing enough shear to hinder any development in the Caribbean. A fairly persistent wave is over the northern Windward Islands. This wave has had a good low level circulation for a couple of days but has been imbedded in a dry airmass and has not been able to develop any significant convection. However, overnight last night the convection did improve quite a bit. It’s gradually moving into a more moist environment in the eastern Caribbean but it’s also moving into that strong shear created by the upper level low in the Bahamas. IR and WV loops show that some of that shear is already impeding on that wave.

In the Atlantic…

The ITCZ is fairly active along 10N all the way from the African coast to about 48W. There is a large area of Saharan Air evident of visible satellite images from the African coast all the way to about 55W and extending from about 15N to about 25N. A fairly well developed wave lies near 11N 38W. Most of the convection with this wave is well east of the low level circulation. The models want to develop this system into a hurricane and move it generally NW. Right now the wave lies too close to the ITCZ to classify it as a tropical depression.. And if it develops the way the models want to develop it, it’ll move well into that SAL air to the north of it. So based on the models, I’d say this system may not have much of a chance to develop. It’ll be a different story if the wave continues a westward track.

There’s a lot of convection along the ITCZ in the eastern Atlantic but nothing organized.

Have a great Saturday!!!!!

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Tropical Discussion Fri Sept 1st 6:00am CDT

By: LRandyB, 11:12 AM GMT on September 01, 2006

Good morning folks! Not a lot of change from yesterday afternoon in the tropics.

In the Gulf.....

That area of dry air in the Gulf continues to push south on WV images and now covers most of the Gulf. No waves, upper level lows, or... clouds for that matter, to speak of in most of the Gulf of Mexico this morning.

In the Caribbean......

Upper level ridging that extends from Ernesto has enhanced some of the convection from daytime heating yesterday and generally has increased the moisture over the western third of the Caribbean. The eastern two thirds of the Caribbean are occupied by dry air under high pressure and generally low level easterly winds.

In the western Atlantic....

Ernesto is making his way overland in east central NC. He almost made hurricane strength last night and this morning continues to hold TS strength. But the highest winds have, for the most part, been over water. Ernesto is expected to continue it's track north and become an extratropical low somewhere up around the eastern Great Lakes.

That upper level low I talked about yesterday is still spinning north of Puerto Rico. And another at 27N 42W is tracking west in the deep easterly flow of the central Atlantic.

In the Atlantic...

A persistant easterly wave located near 16N 54W has been moving west at a steady pace. Convection has been flaring with this wave diurnally but then always calms back down again. It has good rotation on daytime visible images but is imbedded in a dry airmass for the moment. We will have to watch this one as it makes it's way acrss the Atlantic.

Another tropical wave is near 13N 37W. Convection has flared dirunally with this one too but never seems to persist. And this one isn't in the dry air so bears watching as well.

There is a lot of convective activity in the ITCZ, especially off Africa but nothing organized as yet. Some of the models do try to develop one or two waves off Africa over the next few days so I'll be keeping an eye on the eastern and central Atlantic

I hope everyone has a great Friday and a great weekend!

Randy

Updated: 3:51 AM GMT on September 02, 2006

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I was an AF aviation weather forecaster for 12 years, then 15 years as a dropsonde systems operator with the AF Reserve Hurricane Hunters.

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