ATL SIXTEEN: Tropical Depression - Discussion

[wxman57]

Careful. Those models see something to bend it that far west. They could adjust in 36 hours however and return more to climatology - but that is ALWAYS dependent on real time synoptics. I got burned by Marco assuming what you're assuming now.

The models see a ridge developing over the southeast U.S., Gulf of Mexico, and Florida over the next 3-4 days. Increasing easterly winds in the low to mid levels would steer the system inland into the southern Yucatan by Thursday.

[Blown Away]

Careful. Those models see something to bend it that far west. They could adjust in 36 hours however and return more to climatology - but that is ALWAYS dependent on real time synoptics. I got burned by Marco assuming what you're assuming now.

The models see a ridge developing over the southeast U.S., Gulf of Mexico, and Florida over the next 3-4 days. Increasing easterly winds in the low to mid levels would steer the system inland into the southern Yucatan by Thursday.

Is it possible the circulation center is now near 15.5N/82W which is just S of the latest convection burst just N of this point?

http://www.ssd.noaa.gov/goes/flt/t3/loop-avn.html

[HURAKAN]

699
ABNT20 KNHC 132358
TWOAT
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT MON OCT 13 2008

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON TROPICAL
DEPRESSION NANA...LOCATED ABOUT 1105 MILES WEST OF THE CAPE VERDE
ISLANDS AND ON TROPICAL DEPRESSION FIFTEEN...LOCATED
ABOUT 355 MILES SOUTHWEST OF SAN JUAN PUERTO RICO.

SHOWERS AND THUNDERSTORMS CONTINUE IN ASSOCIATION WITH A BROAD AREA
OF LOW PRESSURE CENTERED IN THE SOUTHWESTERN CARIBBEAN SEA A SHORT
DISTANCE EAST OF THE COAST OF NICARAGUA. UPPER-LEVEL WINDS ARE
VERY FAVORABLE FOR DEVELOPMENT...AND THIS SYSTEM IS LIKELY TO
BECOME A TROPICAL DEPRESSION ON TUESDAY OR WEDNESDAY IF IT REMAINS
OVER WATER. A SLOW MOTION TO THE NORTHWEST NEAR THE COAST OF
CENTRAL AMERICA IS EXPECTED OVER THE NEXT DAY OR TWO. AN AN AIR
FORCE RESERVE UNIT HURRICANE HUNTER AIRCRAFT IS SCHEDULED TO
INVESTIGATE THE SYSTEM ON TUESDAY...IF NECESSARY. REGARDLESS OF
WHETHER OR NOT THIS SYSTEM BECOMES A TROPICAL CYCLONE...IT IS
LIKELY TO PRODUCE LOCALLY HEAVY RAINS OVER PORTIONS OF NICARAGUA...
HONDURAS...AND BELIZE OVER THE NEXT COUPLE OF DAYS.

A WEAK AREA OF LOW PRESSURE...LOCATED SOUTH OF TROPICAL DEPRESSION
NANA AND APPROXIMATELY 1100 MILES WEST OF THE SOUTHERNMOST CAPE
VERDE ISLANDS...COUNTINUES TO GENERATE SOME THUNDERSTORM ACTIVITY.
THIS SYSTEM WILL ENCOUNTER UNFAVOABLE UPPER-LEVEL WINDS OVER THE
NEXT DAY OR TWO AND SIGNIFICANT DEVELOPMENT IS NOT EXPECTED.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

PUBLIC ADVISORIES ON TROPICAL DEPRESSION FIFTEEN ARE ISSUED UNDER
WMO HEADER WTNT35 AND UNDER AWIPS HEADER MIATCPAT5.
FORECAST/ADVISORIES ARE ISSUED UNDER WMO HEADER WTNT25 AND UNDER
AWIPS HEADER MIATCMAT5.

$$

FORECASTER FRANKLIN/SCHAUER CLARK

[HURAKAN]

Aggressive words from the NHC! TD likely tomorrow or WED.

[MiamiensisWx]

The slower short term movement would imply landfall farther south on the Yucatan Peninsula, as well as a (more pronounced) NW turn. It's very hard to believe this one will precipitously escape a future landfall on Belize or Mexico. However, there is an excellent diffluent environment, as well as dual outflow channels (aided by the southwesterly wind vectors associated with retrograding TUTT over mainland Mexico and the 250-500 mb trough to the NE of the budding TC). The slow movement suggests the system has a good opportunity to attain strong TS/hurricane status, depending on its proximity to the mountainous countries of Honduras and Nicaragua. In the short term, downsloping off the mountains will mitigate more rapid organization and hinder the formation of an inner core. Of course, the broad nature of the system (and surface low) is another short term negative factor as well.

[MGC]

Greeting from Va Beach....Tropics have become quite active the past several days, just in time for my vacation. I'm up visiting my grand kids!

This disturbance has a very good chance to develope into a TD tomorrow or Wednesday. With the ULL over the BOC retrograding away, an excellent UL enviroment shoud exist over the disturbance and as long as it remains over water it should spin. I think a Yucatan landfall is most likely.

Gotta run the baby needs his diaper changed.......MGC

The above opinion is that of MGC and not an official forecast.

[wxman57]

The GFS is forecasting the ridge over the SE U.S. to be fairly strong by Thursday. Increasing mid to low-level flow across the NW Caribbean would push 99L inland on Thursday morning - possibly across southern MX into the East Pac. I don't buy the EC solution of stalling it near the northern Yucatan and it sitting there for 10+ days.

Here's a 700-400mb mean flow chart valid noon Thursday:

[gatorcane]

Wxamn it depends what part of Thursday you are talking about. That is when the mid-scale synoptics start to change across the SE US as the trough approaches. For Thursday morning, the image you have above is accurate. But check out 96 hours from 18Z GFS. The center of the H5 ridge is already starting to move east over Southern FL....with return flow from the south on the left side:



Now into later this weekend, very sharp trough here:



Perhaps the Euro is on to something, it does seem to get the large-scale synoptics better for the long-range so we shall see. It would seem that if 99L gets deep enough (which would imply it festers over the NW Caribbean or near/off Belize into Thurs/Friday or so), it would have a better chance of slipping into a weakness with the setup unfolding. If it stays shallow, probably not.

[Nimbus]

Even if 99l crosses the Yucatan and meanders in the western gulf it could get pulled back northeast into the mid gulf coastline as a weaker system.

[Blown Away]

Gatorcane, you make a good point, but regardless I don't think that sharp trough will be enough to pull 99L out of the Caribbean. I think 99L gets left behind, the question is will it hang out over water or land. I look at the subtle sometimes meaningless turns of the models, I see the HWRF stalling very near the coast and the GFDL hinting a N turn just after making landfall in the Yucatan, the next round of models will give a better indication IMO. I'll be looking at the end run of the models for that N turn. I'm not sold on 99L crossing the Yucatan into the BOC or EPAC and it's not that uncommon for systems to sit and spin in this area for many days.

[MiamiensisWx]

Even if 99l crosses the Yucatan and meanders in the western gulf it could get pulled back northeast into the mid gulf coastline as a weaker system.

I personally disagree. The orientation of the ridging (as progged by the operational GFS, GFS ensembles, and Euro) and the location of both amplifying troughs would actually suggest a WSW movement over land toward the southern Bay of Campeche and mainland Mexico. As the system weakens over land and becomes less responsive to mid/upper level steering currents, a drifting motion or WSW movement seems probable. In fact, there are some similar historical climatological analogs in regards to the upcoming pattern and 99L's timing location.

Specifically, Storm #4 (1922) is a very interesting one. Overall, 99L's track and life cycle may be very similar; the main difference may be the fact that 99L will make landfall farther south than the 1922 TC. Interestingly, the 1922 hurricane likely struck Mexico as a strong Category 2 hurricane (90-95 kt) based on historical accounts and data. It also moved very slowly prior to landfall. Since 99L will encounter very favorable synoptic/thermodynamic conditions and UL support, a strong TS/hurricane is very probable, and the slow movement will allow ample time over water. The main limiting factor will be land interaction (downsloping off Honduras/Nicaragua) within the short term.

1922 analog:

http://weather.unisys.com/hurricane/atlantic/1922/4/track.gif

If you traverse the historical records, many similar October systems were situated near 99L's general vicinity and still turned WNW into Central America or the Yucatan Peninsula.

[AJC3]

Even if 99l crosses the Yucatan and meanders in the western gulf it could get pulled back northeast into the mid gulf coastline as a weaker system.

Very, very unlikely.

[MiamiensisWx]

I personally disagree. The orientation of the ridging (as progged by the operational GFS, GFS ensembles, and Euro) and the location of both amplifying troughs would actually suggest a WSW movement over land toward the southern Bay of Campeche and mainland Mexico. As the system weakens over land and becomes less responsive to mid/upper level steering currents, a drifting motion or WSW movement seems probable. In fact, there are some similar historical climatological analogs in regards to the upcoming pattern and 99L's timing location.

Specifically, Storm #4 (1922) is a very interesting one. Overall, 99L's track and life cycle may be very similar; the main difference may be the fact that 99L will make landfall farther south than the 1922 TC. Interestingly, the 1922 hurricane likely struck Mexico as a strong Category 2 hurricane (90-95 kt) based on historical accounts and data. It also moved very slowly prior to landfall. Since 99L will encounter very favorable synoptic/thermodynamic conditions and UL support, a strong TS/hurricane is very probable, and the slow movement will allow ample time over water. The main limiting factor will be land interaction (downsloping off Honduras/Nicaragua) within the short term.

1922 analog:

http://weather.unisys.com/hurricane/atlantic/1922/4/track.gif

If you traverse the historical records, many similar October systems were situated near 99L's general vicinity and still turned WNW into Central America or the Yucatan Peninsula.

Tony,

Do you concur with this general idea?

[AJC3]

I personally disagree. The orientation of the ridging (as progged by the operational GFS, GFS ensembles, and Euro) and the location of both amplifying troughs would actually suggest a WSW movement over land toward the southern Bay of Campeche and mainland Mexico. As the system weakens over land and becomes less responsive to mid/upper level steering currents, a drifting motion or WSW movement seems probable. In fact, there are some similar historical climatological analogs in regards to the upcoming pattern and 99L's timing location.

Specifically, Storm #4 (1922) is a very interesting one. Overall, 99L's track and life cycle may be very similar; the main difference may be the fact that 99L will make landfall farther south than the 1922 TC. Interestingly, the 1922 hurricane likely struck Mexico as a strong Category 2 hurricane (90-95 kt) based on historical accounts and data. It also moved very slowly prior to landfall. Since 99L will encounter very favorable synoptic/thermodynamic conditions and UL support, a strong TS/hurricane is very probable, and the slow movement will allow ample time over water. The main limiting factor will be land interaction (downsloping off Honduras/Nicaragua) within the short term.

1922 analog:

http://weather.unisys.com/hurricane/atlantic/1922/4/track.gif

If you traverse the historical records, many similar October systems were situated near 99L's general vicinity and still turned WNW into Central America or the Yucatan Peninsula.

Tony, Do you concur with this general idea?

That seems the most likely solution. And like i've been saying all day, Even if the DLM easterly flow does not drive 99L to it's death over MX/CENAM (which I agree with you and Chris as being the most viable solution), there is still no support for the trough to actually pick up the system so that it makes a run at FL over the next week. The trough axis amplifies too far east...period. Unless you see the model guidance dig the late week trough about 5 to 10 degrees to the west, there will be not be the necessary deep layer SW flow to draw the system out to the northeast.

The 10-day ECM meander over the western Caribbean also looks very unlikely to me.

[wxman57]

:uarrow:
Wxamn it depends what part of Thursday you are talking about. That is when the mid-scale synoptics start to change across the SE US as the trough approaches. For Thursday morning, the image you have above is accurate. But check out 96 hours from 18Z GFS. The center of the H5 ridge is already starting to move east over Southern FL....with return flow from the south on the left side:

http://www.nco.ncep.noaa.gov/pmb/nwprod ... 0_096l.gif

Now into later this weekend, very sharp trough here:

http://www.nco.ncep.noaa.gov/pmb/nwprod ... 0_126l.gif

Perhaps the Euro is on to something, it does seem to get the large-scale synoptics better for the long-range so we shall see. It would seem that if 99L gets deep enough (which would imply it festers over the NW Caribbean or near/off Belize into Thurs/Friday or so), it would have a better chance of slipping into a weakness with the setup unfolding. If it stays shallow, probably not.

gatorcane,

Here are the same mean flow charts from the 18Z GFS for Friday and Saturday. Continued easterly steering currents Friday then NE flow Saturday by Honduras. Nothing to bring the system northward:

Friday 18Z:


Saturday 18Z

[Ed Mahmoud]

I have no idea where 99L will go, and if the professionals say Central America, they are probably right.


But I do recall the first forecasts for Mitch in the Caribbean. Of course, then Mitch was forecast initially to come North/Northwest out of the Caribbean, and it instead meandered Southwest. So this would have to be backwards of that error.

So, in my amateur opinion, waiting a couple more model cycles before giving Florida the all clear, especially when Joe Bastardi is talking similarities to Hazel, well, in my unofficial and amateur opinion, I can wait a day or two.

[AJC3]

So, in my amateur opinion, waiting a couple more model cycles before giving Florida the all clear, especially when Joe Bastardi is talking similarities to Hazel, well, in my unofficial and amateur opinion, I can wait a day or two.

This I can agree with. I'd never give a 100% definitive all clear this early, and have suggested what would need to change in the guidance for other outcomes to be more seriously considered. But as mets, we'd be remiss if we didn't point out the (un)likelihood or feasability of the various possibilites that have been suggested in this thread.

[Sanibel]

Shortwave shows a vortex near 16N-81.5W

This is much more overwater than the models indicate even if it does turn west.

[HurricaneRobert]

GFDL keeps showing a track similar to Hattie, not Hazel.

[TheEuropean]

14/0545 UTC 14.9N 82.5W T1.0/1.0 99L -- Atlantic Ocean

Convection is popping up near the border of Honduras to Nicaragua. Could this track even further north into the yucatan?