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

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

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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


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1600. flaboyinga
3:05 PM GMT on October 03, 2007
There's a small counterclockwise spin kicking up at 10N,60W.
1599. WXMongrel
2:49 PM GMT on October 03, 2007
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
1598. thelmores
2:44 PM GMT on October 03, 2007
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???
Member Since: September 8, 2005 Posts: 0 Comments: 3805
1597. SomeRandomTexan
2:43 PM GMT on October 03, 2007
IceSlater----

that is correct.... i was speaking in refernce to what the models show over the next few days....
Member Since: August 30, 2007 Posts: 0 Comments: 1857
1596. NEwxguy
2:43 PM GMT on October 03, 2007
wow,everyone's getting confused with all these invests
Member Since: September 6, 2007 Posts: 887 Comments: 15972
1595. LakeShadow
2:42 PM GMT on October 03, 2007
new blog's posted
Member Since: August 10, 2007 Posts: 3 Comments: 2134
1594. SomeRandomTexan
2:42 PM GMT on October 03, 2007
IKE---

true.... anything can happen as of right now...
Member Since: August 30, 2007 Posts: 0 Comments: 1857
1593. druseljic
2:42 PM GMT on October 03, 2007
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...
Member Since: August 13, 2007 Posts: 0 Comments: 655
1592. IceSlater
2:41 PM GMT on October 03, 2007
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.
Member Since: July 6, 2005 Posts: 0 Comments: 417
1590. Tazmanian
2:41 PM GMT on October 03, 2007
i think we have seen all we are going to see out of 90L but i give it one more day
Member Since: May 21, 2006 Posts: 5091 Comments: 115437
1589. IKE
2:40 PM GMT on October 03, 2007
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.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
1588. nash28
2:40 PM GMT on October 03, 2007
92L out to sea???

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

92L will not curve out to sea.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
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...
Member Since: August 30, 2007 Posts: 0 Comments: 1857
1586. LakeShadow
2:39 PM GMT on October 03, 2007
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?
Member Since: August 10, 2007 Posts: 3 Comments: 2134
1585. louisianaboy444
2:39 PM GMT on October 03, 2007
ooo dont say that WX lol everyone in florida will be on your case
Member Since: August 29, 2006 Posts: 22 Comments: 1352
1584. nash28
2:38 PM GMT on October 03, 2007
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.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1583. franck
2:38 PM GMT on October 03, 2007
Wow...90, 91 and 92. 'Imagicaning' everywhere.
Member Since: August 30, 2005 Posts: 0 Comments: 1150
1582. WXMongrel
2:37 PM GMT on October 03, 2007
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.
1581. quackquack
2:37 PM GMT on October 03, 2007
test
1580. Muffelchen
2:37 PM GMT on October 03, 2007
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 :-)
Member Since: August 21, 2007 Posts: 0 Comments: 72
1579. IceSlater
2:37 PM GMT on October 03, 2007
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?
Member Since: July 6, 2005 Posts: 0 Comments: 417
1578. Crisis57
2:36 PM GMT on October 03, 2007
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
1577. weatherboyfsu
2:36 PM GMT on October 03, 2007
Things are definitely getting interesting east of the bahamas.......
Member Since: July 17, 2005 Posts: 0 Comments: 1025
1576. LakeShadow
2:36 PM GMT on October 03, 2007
any time now, gulfbreezewill. anytime now...
Member Since: August 10, 2007 Posts: 3 Comments: 2134
1575. Progster
2:34 PM GMT on October 03, 2007
Club Gitmo indeed...home of runway orange for imported "supermodels" :)
Member Since: September 4, 2007 Posts: 0 Comments: 491
1574. hurricane23
2:33 PM GMT on October 03, 2007
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
Member Since: May 14, 2006 Posts: 8 Comments: 13841
1573. quackquack
2:33 PM GMT on October 03, 2007
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.
1572. NEwxguy
2:33 PM GMT on October 03, 2007
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.
Member Since: September 6, 2007 Posts: 887 Comments: 15972
1571. SomeRandomTexan
2:33 PM GMT on October 03, 2007
progster---

is that club gitmo.... the tropical jihadist resort?....lol
Member Since: August 30, 2007 Posts: 0 Comments: 1857
1570. IKE
2:32 PM GMT on October 03, 2007
The latest(12Z) NAM model completely washes out 90L...in 54 hours.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
1569. Tazmanian
2:32 PM GMT on October 03, 2007
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?
Member Since: May 21, 2006 Posts: 5091 Comments: 115437
1568. Progster
2:32 PM GMT on October 03, 2007
Looks pretty juicy S of Gitmo..max dBz 60 but no rotationLink
Member Since: September 4, 2007 Posts: 0 Comments: 491
1567. gulfbreezewill
2:32 PM GMT on October 03, 2007
Does anyone know when Dr. Masters typically does his updates?
1565. Melagoo
2:31 PM GMT on October 03, 2007
hey looks like the Avatars work :c)
Member Since: July 31, 2006 Posts: 19 Comments: 1607
1564. PSLcanerider
2:30 PM GMT on October 03, 2007
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 )
Member Since: September 12, 2007 Posts: 0 Comments: 16
1563. IKE
2:30 PM GMT on October 03, 2007
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.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
1562. donedeal
2:30 PM GMT on October 03, 2007
HouseofGryffindor where on the West Coast are you located?
1561. SomeRandomTexan
2:30 PM GMT on October 03, 2007
lol.... year of the non-existant cold fronts...lol
Member Since: August 30, 2007 Posts: 0 Comments: 1857
1560. IceSlater
2:29 PM GMT on October 03, 2007
Did 92L just tighten up a bit to the SE? Or is it just fading...
Member Since: July 6, 2005 Posts: 0 Comments: 417
1559. Patrap
2:29 PM GMT on October 03, 2007
UNYSIS 10-day GFSx is interesting too.

Link
Member Since: July 3, 2005 Posts: 427 Comments: 129442
1558. SomeRandomTexan
2:28 PM GMT on October 03, 2007
cane23----

good link....
Member Since: August 30, 2007 Posts: 0 Comments: 1857
1557. hurricane23
2:28 PM GMT 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.
Member Since: May 14, 2006 Posts: 8 Comments: 13841
1556. Patrap
2:27 PM GMT on October 03, 2007
The early Tracks stop when the Front closes on the system,just pass the 120 hr mark.The later runs should be interesting ..
Member Since: July 3, 2005 Posts: 427 Comments: 129442
1555. sporteguy03
2:27 PM GMT on October 03, 2007
Ike,
So much for the cold fronts??
Member Since: July 7, 2005 Posts: 0 Comments: 5417
1554. SomeRandomTexan
2:26 PM GMT on October 03, 2007
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
Member Since: August 30, 2007 Posts: 0 Comments: 1857
1552. hurricane23
2:26 PM GMT on October 03, 2007
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.
Member Since: May 14, 2006 Posts: 8 Comments: 13841
1551. IKE
2:25 PM GMT on October 03, 2007
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!
Member Since: June 9, 2005 Posts: 23 Comments: 37860
1550. flaboyinga
2:25 PM GMT on October 03, 2007
Looking at the link again, the dry air W of 90L is almost 90% of the dry air on the Atl WV Chart.

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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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