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Little change to 90L; first half of October hurricane outlook

By: Dr. Jeff Masters, 7:09 PM GMT on October 02, 2007

A low pressure system over the southeastern Gulf of Mexico (90L) has changed little today. The buoy 262 nm south of Panama City, FL had winds of 36 mph gusting to 45 mph this morning, but these winds have fallen some this afternoon. Satellite loops show some disorganized heavy thunderstorm activity that is not increasing in intensity. This system has the potential to become a subtropical depression by Wednesday, and a Hurricane Hunter aircraft is scheduled to investigate the system Wednesday afternoon. This afternoon's model runs continue to point to a landfall Thursday or Friday in Louisiana or Texas. I don't see this storm becoming a hurricane, due to the large amount of dry air to overcome, plus the extended amount of time it will take to transition from a subtropical to a tropical storm. The GFDL model probably has the right idea, bringing 90L ashore in Texas Friday with top winds near 40-45 mph.

First half of October hurricane outlook
In the first half of October, Atlantic tropical cyclone activity remains high, and is in the final two weeks of its peak phase. Since the current active hurricane period began in 1995, the first half of October has given birth to an average of 1.9 named storms, 0.75 hurricanes, and 0.3 intense hurricanes. For October through December, these figures are 3.8 named storms, 1.7 hurricanes, and 0.75 intense hurricanes. These numbers are nearly double the long-term climatological averages for the past 100 years. The final seasonal forecast from the Phil Klotzbach/Dr. Bill Gray team at Colorado State University, issued today, calls for four named storms, two hurricanes, and one intense hurricane for the remainder of this year.

October storms form from tropical waves that come off the coast of Africa, and from the remains of old fronts that push off the coast of the U.S. As we can see from the track plot of all first half of October storms (Figure 1), there is a lot of activity during the period, but relatively few storms form out near the African coast. The water temperatures off the coast of Africa are starting to cool and be marginal for hurricane formation, and wind shear is starting to pick up in its normal fall cycle.


Figure 1. Tracks of all tropical storms and hurricanes since 1851 that formed October 1-15. There are very few storms forming off the coast of Africa during this period.

Sea Surface Temperatures
Sea Surface Temperatures (SSTs) have been about 0.5 °C above average over the Caribbean and Gulf of Mexico the past few weeks (Figure 2). This is the primary formation area for October storms. Note also the tongue of colder than average SSTs extending out into the Pacific Ocean from the coast of South America. This is the signature of a moderate strength La Niña event.


Figure 2. Sea Surface Temperature (SST) departure from average for the end of September. Image credit: NOAA.

Tropical Cyclone Heat Potential
It's not just the SSTs that are important for hurricanes, it's also the total amount of heat in the ocean to a depth of about 150 meters. Hurricanes stir up water from down deep due to their high winds, so a shallow layer of warm water isn't as beneficial to a hurricane as a deep one. The Tropical Cyclone Heat Potential (TCHP, Figure 3) is a measure of this total heat content. A high TCHP over 80 is very beneficial to rapid intensification. There are similar levels of heat energy available in the Western Caribbean and Gulf of Mexico this year compared to the devastating Hurricane Season of 2005. Recall that Wilma, the most intense hurricane on record, formed on October 15 of that year.


Figure 3. Tropical Cyclone Heat Potential (TCHP) for September 30 2005 (top) and September 30 2007 (bottom). TCHP is a measure of the total heat energy available in the ocean. Image credit: NOAA/AOML.

Wind shear
Wind shear is usually defined as the difference in wind between 200 mb (roughly 40,000 foot altitude) and 850 mb (roughly 5,000 foot altitude). In most circumstances, wind shear above 20 knots will act to inhibit tropical storm formation by tearing a storm apart. Wind shear 10 knots and lower is very conducive for tropical storm formation.

Despite the presence of a La Niña event the past month--which is supposed to bring lower than average wind shear to the tropical Atlantic--wind shear the past two weeks has been above average (Figure 4). The latest two-week wind shear forecast from the GFS model predicts near-average wind shear for the first half of October.


Figure 4. Wind shear departure from average for the 11 days ending September 29. Above average levels of wind shear were observed over the Caribbean and Gulf of Mexico. Wind shear is the difference in wind between 200 mb (roughly 40,000 foot altitude) and 850 mb (roughly 5,000 foot altitude) in meters per second (multiply by two to get the approximate wind shear in knots).

Steering currents
The steering current pattern for the last half of September has been dominated by a strong ridge of high pressure over the Eastern U.S. This ridge is expected to remain in place until at least October 12, and will reduce the tendency of storms to recurve out to sea. Long range forecasts from the GFS and ECMWF models foresee the ridge may break down beginning October 12, but it is too early to be confident of this.

Summary
I predict two named Atlantic storms will form in the first half of October. One of these storms will probably be 90L. Several models, including the GFS, have been hinting at formation of a tropical depression in the Bahamas, Western Caribbean, or Gulf of Mexico sometime in the next 4-7 days. The upper air environment is forecast to be favorable for intensification over the Gulf of Mexico next week, with low wind shear.

Jeff Masters


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

Reader Comments

morning all. Interesting developments... Anything to those blobletts in the mid atlantic? Is shear still tearing things apart out there?
This is a question for anybody that wants to answer with regards to 92L considering the current circumstances is this a big rain event or a hurricane for Miami?
None of these invests look particulatly promising in terms of development.
90L looks really disorganised;
91L too big and currently disorganised;
92L looks great but can't see any cyclonic rotation.
If it keeps developing at the rate it's been doing this am. I don't think it will take days to develop. The environment is to favorable. Low shear, moist atmosphere & very warm water not much land to inhibit it. Just my take.
poikoo 9:01 AM CDT on October 03, 2007
is 92 going to bring any rain to tampa area or go way south of the state?

Way too early to even speculate (although models do)....Agree with the earlier comment that the models have problems with "weak" systems.......We will have to wait to see if the system develops into a TD/TS before the models can start to get a handle on possible tracks.....It may never develop into anything other than an off-shore rain event....
lol the computer models have 92L going near florida i guess that is all you will hear about for the next few days....can someone post a link to where i can get some information on 90L any help will be appreciate thanks!
1507. Patrap
Happy Birthday Sheri!
Link
I am just wondering is 92L the old Karen? or is she totally gone?
1509. IKE
If anyone has a link for the models to 92L, could you post it here?

Thanks.
1510. IKE
catastropheadjuster 9:07 AM CDT on October 03, 2007
I am just wondering is 92L the old Karen? or is she totally gone?


It's not Karen...and....

Happy Birthday.
1502. Miamiweather 10:03 AM EDT on October 03, 2007
This is a question for anybody that wants to answer with regards to 92L considering the current circumstances is this a big rain event or a hurricane for Miami?

We'll miami all i can tell you right now is it would suprise me if this became a hurricane before coming close to the florida coast but anything is possible as SST'S are warm and other conditions look somewhat favorable for some intensification before coming close to florida.These are the first models for 92L and as we all know things can change.Ships has this system as a 90kt hurricane in the gulf.

I would say a 50mph TS is not out of the question but it would have to start getting better organized sooner rather then later.Either way more rain for us looks like a good bet. Adrian
good morning you guys!!!

well it looks like txalwaysprepared and my wishcasting has paid off...lol...lol.... looks like 90L will be more of a Louisianna storm....YES!!!..... and it also looks very very disorganized..... prob wont even make TD status.... What do you guys think? PATRAP?
Patrap: Thank You for the cake. Hope you have a great day. Keep up all the good work you do on here to keep us updated. I live in LA (lower Alabama).
Sheri
ty hurricane 23 I appreciate it
1515. 606
The tropical wave in the Atlantic looks impressive. Does anyone have information on this system.
1509. IKE 10:08 AM EDT on October 03, 2007
If anyone has a link for the models to 92L, could you post it here?

Thanks.

Here you go. 3 links

1-SFWD models
2-WU models
3-Colorado state models Click on Early-cycle track guidance frame 3.
IKE: Thank you. Thanks for answering my question. I just didn't know if it was or wasn't.
1518. IKE
Thanks 23.
Is 91L the remnants of Karen?

92L looked really impressive yesterday it was firing a lot of convection, but this morning it isnt near what it was....
1520. Patrap
92L one to watch
1521. IKE
I have a hard time believing 92L will go WSW...in October. That has to be a strong high.
yeah you right texan 92L isnt near what it was yesterday...theres no cyclonic turning yet....should just be a heavy rain maker for south florida....that could be a good thing lol
The good Dr. Masters must be writing one huge blog for it to take this long.... doesn't he have them up by now? I guess there is plenty to start discussing in the tropics at this point.... looks to be a busy beginning to October....
RECON flight for the bahamas!

4. SUSPECT AREA (BAHAMAS)
FLIGHT ONE --TEAL 72
A. 04/1800Z
B. AFXXX 01KKA INVEST
C. 04/1445Z
D. 25.0N 74.0W
E. 04/1730Z TO 2100Z
F. SFC TO 10,000 FT

FLIGHT TWO --TEAL 73
A. 05/0600Z
B. AFXXX 02KKA CYCLONE
C. 05/0200Z
D. 25.0N 75.0W
E. 05/0500Z TO 0900Z
F. SFC TO 10,000 FT

5. OUTLOOK FOR SUCCEEDING DAY: BEGIN 6 HRLY FIXES AT
05/1800Z IF SYSTEM DEVELOPS.
Also just testing new blog
From what I understand, the La Nina has set up in the Pacific...why then is wind shear still a big factor in the Atlantic...? Anyone know this?
1527. Michfan
AFAIK 91L is not the remnants of Karen. Its too far south to be so. Karen got sheared to shreds NE of the Lesser Antilles a few days ago.
Most of the dry air around 90L is on the W side or to the S of it.

LABoy-----

from what I understand SFL could really use the rain.... looks like you guys may get a little wet off of 90L.... hope it doesnt flood or anything, looks to be a small system so it prob wont...gl
Is this a year of weather anomolies? Right now its almost 80 degrees in B-lo and I have strawberries still growing in my garden, tomato plants are still flowering...What gives?
Patrap, is Recon scheduled to check out 90L or is this just going to stay a rainmaker?
Recon flights for 92L were just posted for those interested in viewing.
Muffelchen 2:05 PM GMT on October 03, 2007 Hide this comment.
None of these invests look particulatly promising in terms of development.
90L looks really disorganised;
91L too big and currently disorganised;
92L looks great but can't see any cyclonic rotation.


I gotta agree with you ont his,i was suprised to see 2 new invests,but 92L still can be hazardous
michfan--- im sorry i meant melissa.....

i thought dr masters said that the remnants of Karen would mix with 92L and form something....
1531. hurricanehanna 10:19 AM EDT on October 03, 2007
Patrap, is Recon scheduled to check out 90L or is this just going to stay a rainmaker?
Action: | Ignore User

Look up i just posted the recon info...Its for 92L in the bahamas.
I really dont think florida will get much from 92L maybe some pockets of heavy rain but thats about it....looks to stay to the south of florida right now might turn into a depression after that we will have to see
Testing
Pat , re 1520

It says 'acces forbidden' when you go there.
1540. tropicofcancer 10:20 AM EDT on October 03, 2007
Pat , re 1520

It says 'acces forbidden' when you go there.

Look at my post above all 3 model links were posted includeing colorado state models.


1516. hurricane23 10:13 AM EDT on October 03, 2007
cane23---
i got the same message
South Florida doesn't need the rain we're pretty flooded already. Central, North & West are the ones that need the rain.
on top of good conditions for 92L, we are having mid summer temps... highs today and tomorrow 91 (and with high humidity the heat index is crazy) it was 80 this morning at 6am.

No October weather going on around here.
donedeal----

sorry, well hope you dont get anymore rain.... i had just heard some floridians yesterday say they were needing some rain.... gl with 92L
1538. louisianaboy444 10:20 AM EDT on October 03, 2007
I really dont think florida will get much from 92L maybe some pockets of heavy rain but thats about it....looks to stay to the south of florida right now might turn into a depression after that we will have to see

I would have to disagree on your thoughts right now as development could indeed take shape in the bahamas and as far as models this is the first run lol.
Thanks H23
1548. Patrap
Prompt error on the Access Forbidden..They sensitive sometimes.
Yeah Ike, none of the Global Models have been run yet on 92L see what they show, but a WSW dive is a pretty strong High.
Looking at the link again, the dry air W of 90L is almost 90% of the dry air on the Atl WV Chart.
1551. IKE
Here's my forecast for Columbus Day...which is Monday....Florida panhandle....

"Columbus Day
Partly cloudy with a 20 percent chance of showers and thunderstorms. Highs 86 to 91.

Normal high is 82!
Folks need to read through the blog more carefully i posted all 3 links to good models sites for tropical invest.

Colorado State models-Click on Early-cycle track guidance and then hit frame 3.
looking at the firs model runs.... does it look like 93L will be a mexico storm.... kinda strange to see a system moving to the sw this late in the year but i guess anything can happen... or will this system curve around the high and hit texas or louisianna....thanks
Ike,
So much for the cold fronts??
1556. Patrap
The early Tracks stop when the Front closes on the system,just pass the 120 hr mark.The later runs should be interesting ..
For those who missed it....

4. SUSPECT AREA (BAHAMAS)
FLIGHT ONE --TEAL 72

A. 04/1800Z
B. AFXXX 01KKA INVEST
C. 04/1445Z
D. 25.0N 74.0W
E. 04/1730Z TO 2100Z
F. SFC TO 10,000 FT

FLIGHT TWO --TEAL 73
A. 05/0600Z
B. AFXXX 02KKA CYCLONE
C. 05/0200Z
D. 25.0N 75.0W
E. 05/0500Z TO 0900Z
F. SFC TO 10,000 FT

5. OUTLOOK FOR SUCCEEDING DAY: BEGIN 6 HRLY FIXES AT
05/1800Z IF SYSTEM DEVELOPS.
cane23----

good link....
1559. Patrap
UNYSIS 10-day GFSx is interesting too.

Link
Did 92L just tighten up a bit to the SE? Or is it just fading...
lol.... year of the non-existant cold fronts...lol
HouseofGryffindor where on the West Coast are you located?
1563. IKE
sporteguy03 9:27 AM CDT on October 03, 2007
Ike,
So much for the cold fronts??


Not having a cold front may save us with 92L.

But yeah, I'd love to see some fall weather that lasts for awhile.
does anyone else notice the spin starting in 91L. And what are the reasons for a fish storm ? (been lurking for a while, just trying to learn )
1565. Melagoo
hey looks like the Avatars work :c)
Does anyone know when Dr. Masters typically does his updates?
Looks pretty juicy S of Gitmo..max dBz 60 but no rotationLink
1557. hurricane23 7:28 AM PDT on October 03, 2007
For those who missed it....

4. SUSPECT AREA (BAHAMAS)
FLIGHT ONE --TEAL 72
A. 04/1800Z
B. AFXXX 01KKA INVEST
C. 04/1445Z
D. 25.0N 74.0W
E. 04/1730Z TO 2100Z
F. SFC TO 10,000 FT

FLIGHT TWO --TEAL 73
A. 05/0600Z
B. AFXXX 02KKA CYCLONE
C. 05/0200Z
D. 25.0N 75.0W
E. 05/0500Z TO 0900Z
F. SFC TO 10,000 FT

5. OUTLOOK FOR SUCCEEDING DAY: BEGIN 6 HRLY FIXES AT
05/1800Z IF SYSTEM DEVELOPS.


23 are they going out today for 92L?
1570. IKE
The latest(12Z) NAM model completely washes out 90L...in 54 hours.
progster---

is that club gitmo.... the tropical jihadist resort?....lol
1572. NEwxguy
expecting way above normal temps here in Mass.
if it was August or early Sept.I would be worried about the action down there,but our tropical season is over. Lot of fronts marching across the US.
I hate when they pop up so close 92l.Leaving from lake worth Fl on Fri to go to Orlando.I hope I don't have to shutter up before I go.
If your looking for tropical cyclone models and satelitte views here are a couple of links from my website.

1-My Tropical Links Page
2-Atlantic satelitte imagery page
3-My forcast models page
Club Gitmo indeed...home of runway orange for imported "supermodels" :)
any time now, gulfbreezewill. anytime now...
Things are definitely getting interesting east of the bahamas.......
good morning everyone i see the disturbance by the bahamas has been labeled any thinking this can form? and i see we have another out in the atlantic
Here is an interesting note... To me, it looks like 92L tightened up and moved a bit SE of where we may have "thought" it was... If you look at the models in motion, and/or go frame by frame, you will see that they have 92L pushing a bit EAST at first and then going with the W/WSW motion...

Thoughts anyone?
1554. SomeRandomTexan 2:26 PM GMT on October 03, 2007 Hide this comment.
looking at the firs model runs.... does it look like 93L will be a mexico storm....


SRT: I trust you mean 90L. My brain can't cope with four invests and neither can the models I think :-)
test
Ok, amateur prognosticater here is betting that 92L will drift out to sea. It has all the characteristics of a high pressure cell with anti-cyclonic rotation and no defined COC.
1583. franck
Wow...90, 91 and 92. 'Imagicaning' everywhere.
1584. nash28
Agreed with 23 regarding the possible initial impact on FL. This is a very large area of disturbed weather. This is the first set of model runs, which 9 out of 10 times are usually wrong. Let's see how the Upper High evolves and whether a CONUS trough digs down to create any weaknesses.
ooo dont say that WX lol everyone in florida will be on your case
When is the jet stream forcasted to drop latitude in the US? Usually its what brings on our fall weather, but its still way too north. anyone know why?
Muffelchen---

no, it looks like 92L is moving wsw and the models project it to keep moving that way... to early to tell now though... that is the bahama system...
1588. nash28
92L out to sea???

Are you sure you aren't talking about 91L in the ATL?

92L will not curve out to sea.
1589. IKE
The BAM models that have 92L going WSW north of the Yucatan, also had 90L going into the Florida panhandle at first, for what it's worth.
i think we have seen all we are going to see out of 90L but i give it one more day
1587. SomeRandomTexan 2:40 PM GMT on October 03, 2007
Muffelchen---

no, it looks like 92L is moving wsw and the models project it to keep moving that way... to early to tell now though... that is the bahama system...


Random,
It doesn't look like its moving any W at all... and you're incorrect about the models, all of the models show slight EAST movement before it comes back WEST... Which is EXACTLY what it seems to be doing right now.
Whoa, I slept in a bit and now we have 91 and 92 as well. Looks like it might be an interesting couple of days ahead...
IKE---

true.... anything can happen as of right now...
new blog's posted
1596. NEwxguy
wow,everyone's getting confused with all these invests
IceSlater----

that is correct.... i was speaking in refernce to what the models show over the next few days....
I. ATLANTIC REQUIREMENTS
1. SUSPECT AREA (GULF OF MEXICO)
FLIGHT ONE --TEAL 70
A. 03/1800Z
B. AFXXX 01KKA INVEST
C. 03/1600Z
D. 24.0N AND 88.0W
E. 03/1700Z TO 2300Z
F. SFC TO 10,000FT


I have not saw where this was canceled, so I assume its still go???
ok, I did say I was an Amateur...but click on this link, then check the HDW-High Winds box. Tell me these are winds conducive to cyclone development. They are blowing strong in a clockwise direction (anti-cyclonic)...right?

Link
There's a small counterclockwise spin kicking up at 10N,60W.