ATL : TROPICAL DEPRESSION ERIKA (06L)

[MGC]

Yep, convection is firing around 14N.....I'm thinking the northern circulation will be the one to spin. As such, 94L should pass north of the islands and eventually get picked up by the trough in several days. Just my thoughts......MGC

Of course the above is the opinion of MGC and not an official forecast.

[jinftl]

It's been moving wnw to some degree for the last 30 hours...the exact angle has gone up and down, but some variation of wnw since 18z on 8/29 (with the caveat that movements are estimated since there is no real center and reformation could also be the cause of perceived movement)

12 GMT 08/27/09 10.5N 25.6W
18 GMT 08/27/09 10.7N 27.0W
06 GMT 08/28/09 10.2N 32.0W
12 GMT 08/28/09 10.5N 36.0W
18 GMT 08/28/09 11.0N 36.0W
00 GMT 08/29/09 11.3N 37.9W
06 GMT 08/29/09 11.1N 40.0W
12 GMT 08/29/09 11.1N 41.2W
18 GMT 08/29/09 10.6N 42.0W
00 GMT 08/30/09 10.7N 43.4W
06 GMT 08/30/09 11.2N 45.1W
12 GMT 08/30/09 11.8N 46.3W
18 GMT 08/30/09 12.1N 47.5W
00 GMT 08/31/09 12.6N 48.3W

Looks like there is a wnw component in its movement.

[vbhoutex]

With a system this weak and zero evidence of a surface circulation dont rely too heavily on how it looks on sattelite.

It may "look" good but appearances can be decieving. I think all we have here is a weak mid level vortex at best, giving it a circular appearance. The environment around it isnt very conducive at all and im not surprised convection has waned this evening.

Zero evidence? Didn't the NHC mention a surface low in its' discussion earlier? In this case I believe zero evidence is in the eye of the beholder and some of us disagree with you.
It may not be the best environment right now, but as Derek said it is starting to build convection again. We will see if it is indeed just a mid-level vortex that it is firing around or if it is a surface low or if the new convection is helping push the mlv to the surface.

[Gustywind]

000
AXNT20 KNHC 302352
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT SUN AUG 30 2009

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS
OF SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST
FROM THE EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED
ON SATELLITE IMAGERY...METEOROLOGICAL ANALYSIS...WEATHER
OBSERVATIONS...AND RADAR.

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...SPECIAL FEATURES...

AN ACTIVE TROPICAL WAVE EXTENDS FROM 18N45W TO 8N49W WITH AN
ASSOCIATED 1007 MB SURFACE LOW CENTER NEAR 11N48W. THE WAVE IS
MOVING W NEAR 15 KT. SATELLITE IMAGERY INDICATES ELONGATED
CYCLONIC FLOW IN THE VICINITY OF THE WAVE AXIS CONCENTRATED
AROUND THE LOW CENTER. SCATTERED MODERATE/ISOLATED STRONG
CONVECTION IS MAINLY TO THE NW OF THE WAVE AXIS FROM 14N-18N
BETWEEN 47W-49W..AND TO THE W OF LOW CENTER FROM 8N-14N BETWEEN
48W-54W. THIS SYSTEM HAS A HIGH CHANCE...GREATER THAN 50
PERCENT...OF BECOMING A TROPICAL CYCLONE IN THE NEXT 48 HRS.

[jinftl]

The risk could become that 94L misses the trough. The 120 hour (late Friday/early Saturday) forecast point is somewhere in the vicinity of 65W....and possibly south of 20N....if there is a trough moving off the east coast this weekend, it will miss it.

The timing will be crucial, because as the NWS Melbourne is already talking about,

TUE-SAT...(PREVIOUS DISCUSSION) GFS/ECMWF FCST UPPER TROUGH OVER THE
EASTERN U.S. MUCH OF THIS UPCOMING WEEK BUT LIFTING OUT BY THE
WEEKEND.

If 94L is in the vicinity of the forecast models at 120 hours, it will be in a prime spot (possibly) to ride the building ridge west, even if it turns more nw-ly this week.

Yep, convection is firing around 14N.....I'm thinking the northern circulation will be the one to spin. As such, 94L should pass north of the islands and eventually get picked up by the trough in several days. Just my thoughts......MGC

Of course the above is the opinion of MGC and not an official forecast.

[jinftl]

Who knows what the optimal speed would be to catch any troughs? It could be that there is a 48 or 72 hour window for the system to turn west between 2 troughs....and if that window is between days 6 and 10, it could be unfortunate timing.

As the crow flies, the system is about 2300 miles from Miami.

At 10 mph in speed, it is 9.5 days away from Miami.
At 12 mph in speed, it is 7.9 days away from Miami.
At 15 mph in speed, it is 6.3 days away from Miami.

Shows you just how different a small thing like a few miles per hour in forward speed can impact where the system is in the future. 10 mph vs 15 mph...even on identical tracks....could mean the difference between catching trough or missing it. All comes down to timing, 6 days vs 9 days could mean alot....waiting for the front could easily become waiting for the ridge and vice versa.

With all this talk about 94L missing the trough and ridge building in by the time it gets near Dominican Republic, how many days away would it be from south florida on a westward track? Say moving about 15 mph or so?

Sooner might be better for a recurve from SFL/GOM, but I'm not absolutely sure.

[Typhoon_Willie]

Yeah you can see the convection firing up nicely around 14 degrees north latititude now. This system is getting healthier by the hour.

[Ivanhater]

Yep, convection is firing around 14N.....I'm thinking the northern circulation will be the one to spin. As such, 94L should pass north of the islands and eventually get picked up by the trough in several days. Just my thoughts......MGC

Of course the above is the opinion of MGC and not an official forecast.

The problem is, the trough becomes shallow and lifts out allowing the ridge to build back in with stronger heights coming off the east coast behind the trough as well. What I'm watching is just how much latitude this gains in the short term...It is systems like this that makes tropic watching fun to watch

[jinftl]

It's really a game of timing.....move too fast, it will catch the trough. Move slower, it could miss the trough and be steered by developing ridging. Move even slower, it could then be turned out to sea by the next trough, even if it has turned west first. Throw in the track implications of a weaker system vs a stronger one and that adds another level of uncertainty.

How do worst case scenarios come to be? Often it is largely in part to a perfect storm of bad timing.

Yep, convection is firing around 14N.....I'm thinking the northern circulation will be the one to spin. As such, 94L should pass north of the islands and eventually get picked up by the trough in several days. Just my thoughts......MGC

Of course the above is the opinion of MGC and not an official forecast.

The problem is, the trough becomes shallow and lifts out allowing the ridge to build back in with stronger heights coming off the east coast behind the trough. What I'm watching is just how much latitude this gains in the short term...

[Gustywind]

[AtlanticWind]

http://www.ssd.noaa.gov/goes/east/carb/rb-l.jpg

Convection does appear to be refiring

[abajan]

:uarrow:
000
AXNT20 KNHC 302352
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT SUN AUG 30 2009

...SPECIAL FEATURES...

AN ACTIVE TROPICAL WAVE EXTENDS FROM 18N45W TO 8N49W WITH AN
ASSOCIATED 1007 MB SURFACE LOW CENTER NEAR 11N48W...

Granted, it takes more than a low pressure reading/estimate to classify a system as a TD but that's mighty low in my book. I think there's a high probability of an upgrade tomorrow morning.

[vbhoutex]

I think this system is going to have a tough time being picked up by the trough unless it really starts to gain latitude soon. So far it hasn't seemed to be doing a good job of doing that. However, if the convection firing on the North end does spin this up at that point then it should begin to have a better chance to catch the trough if it doesn't slow down any more. Lots of latitude between this system and the East Coast. IMO, it will be nip and tuck whether it gets picked up.

[David in FL]

Well I habe tosay that you guys hae changed your minds so much on this one. Derek at one point said he did not think it would do anything and now we have a GOM EC threat. Am i wrong? What si going on with this thing? Is there a NFL threat?

[jinftl]

Getting picked up by a trough, followed by not developing, are probably the two most likely outcomes. But, what happens after is never known for sure....who would have though that Andrew would make landfall at the same latitude he had reached at 65W? 99 out of 100 times, if you told me that a storm is parallel with Miami at 65W, i would say, no chance of effecting Miami with a landfall.

I think this system is going to have a tough time being picked up by the trough unless it really starts to gain latitude soon. So far it hasn't seemed to be doing a good job of doing that. However, if the convection firing on the North end does spin this up at that point then it should begin to have a better chance to catch the trough if it doesn't slow down any more. Lots of latitude between this system and the East Coast. IMO, it will be nip and tuck whether it gets picked up.

[Ivanhater]

I think this system is going to have a tough time being picked up by the trough unless it really starts to gain latitude soon. So far it hasn't seemed to be doing a good job of doing that. However, if the convection firing on the North end does spin this up at that point then it should begin to have a better chance to catch the trough if it doesn't slow down any more. Lots of latitude between this system and the East Coast. IMO, it will be nip and tuck whether it gets picked up.

I agree David, btw on a side note. They turned your, and my dad's, alma mater Woodham into a middle school last year.

[jinftl]

Please cite any post that even implies a GOM EC threat. Read through the posts and you will understand why such a statement is not valid and not based on any science.

No matter how many times folks try and teach the concept of margin of error and forecast error beyond 5 days, people read what they want to read. No model even goes past 65W due to being beyond 120 hours.

I don't mean to be harsh, i do realize folks have varying levels of understanding of the tropics, and I include myself in this. But we are all here because we have enough of an interest to find a message board to talk the tropics. That is not a mainstream thing....it is a specific topic. I would think there would be a certain level of understanding just by the fact that folks are here.

Well I habe tosay that you guys hae changed your minds so much on this one. Derek at one point said he did not think it would do anything and now we have a GOM EC threat. Am i wrong? What si going on with this thing? Is there a NFL threat?

[tpr1967]

Looking at quickscat this evening and night time Ir 2 visible, i believe the LLC is out near 13.0n 51.0w and the feature farther to the ene is the mid level center. The only way this starts to develop is if (A)The LLC gains alot of convection overnight and forms a new mid level center. (B)The mid level center gathers more convection and works its way down to the surface.Thoughts anyone.

[vbhoutex]

Getting picked up by a trough, followed by not developing, are probably the two most likely outcomes. But, what happens after is never known for sure....who would have though that Andrew would make landfall at the same latitude he had reached at 65W? 99 out of 100 times, if you told me that a storm is parallel with Miami at 65W, i would say, no chance of effecting Miami with a landfall.

I think this system is going to have a tough time being picked up by the trough unless it really starts to gain latitude soon. So far it hasn't seemed to be doing a good job of doing that. However, if the convection firing on the North end does spin this up at that point then it should begin to have a better chance to catch the trough if it doesn't slow down any more. Lots of latitude between this system and the East Coast. IMO, it will be nip and tuck whether it gets picked up.

SSSHHH!!!! They'll hear you!!!

[fci]

Please cite any post that even implies a GOM EC threat. Read through the posts and you will understand why such a statement is not valid and not based on any science.

No matter how many times folks try and teach the concept of margin of error and forecast error beyond 5 days, people read what they want to read. No model even goes past 65W due to being beyond 120 hours.

Well I habe tosay that you guys hae changed your minds so much on this one. Derek at one point said he did not think it would do anything and now we have a GOM EC threat. Am i wrong? What si going on with this thing? Is there a NFL threat?

THANK YOU for pointing out that no post implies a GOM EC threat.
On the contrary, the Pro Mets that post on this site have been unanimous in thier forecast that this will not be an EC or GOM threat.
Wxman advises that the NE Carib needs to be wary of 94L and Derek HAS YET to say anything about an EC or GOM threat!
I go along with the consensus that this will either develop and recurve or poof out.
And I completely agree that Andrew was a rarity that headed due west from pretty far out that would occur about 1 out of 100 times.