Remainder of July hurricane outlook

By: Dr. Jeff Masters , 2:31 PM GMT on July 15, 2009

Share this Blog
3
+

Not much has changed in the Atlantic since my early July Atlantic hurricane outlook posted two weeks ago. Tropical cyclone activity typically picks up a bit during the last half of July, but we are still a month away from when hurricane season really gets going. Since the current active hurricane period began in 1995, nine of 14 years (63%) have had a named storm form during the last half of July. We had two last-half-of-July named storms last year--Christobal and Dolly. As seen in Figure 1, most of the late July activity occurs in the Gulf of Mexico, Western Caribbean, and Carolina waters. However, a few long-track "Cape Verdes" hurricanes begin to occur. These are spawned by tropical waves that come off the coast of Africa. Tropical waves serve as the instigators of about 85% of all major hurricanes.


Figure 1. Tracks of all tropical storms and hurricanes 1851 - 2006 that formed July 16 - 31.The Gulf of Mexico coast is the preferred strike location. There are still very few major Cape Verdes-type hurricanes forming in the last half of July.

Sea Surface Temperatures
Sea Surface Temperature (SST) anomalies have warmed slightly over the past two weeks, and are about 0.3°C (0.5°F) above average over the tropical Atlantic between Africa and Central America (Figure 2). These are some of the coolest SST anomalies for this time of year that we've seen since 1994. The strength of the Azores-Bermuda high has been near or slightly below average over the past two weeks, driving slightly below average trade winds. Weaker trade winds don't mix up as much cold water from the depths, and cause less evaporative cooling. The latest 2-week run of the GFS model predicts continued near-average or slightly below average-strength trade winds through the end of July, so SSTs should remain slightly above average during this period.


Figure 2. Sea Surface Temperature (SST) departure from average for July 13, 2009. SSTs were about 0.3°C (0.5°F) average over the tropical Atlantic's Main Development region for hurricanes, from Africa to Central America between 10° and 20° North Latitude. Note the large region of above average SSTs along the Equatorial Pacific off the coast of South America, the hallmark of a developing El Niño episode. Image credit: NOAA/NESDIS

El Niño
El Niño conditions continue to amplify over the tropical Eastern Pacific. Ocean temperatures in the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region", are now 0.4°C above the threshold for a weak El Niño, according to the Australian Bureau of Meteorology (Figure 3). An increase of another 0.1°C will push the current El Niño into the "moderate" category. NOAA's Climate Prediction Center issued an El Niño Advisory earlier this month. The latest set of mid-June runs of the El Niño computer models are almost universally calling for El Niño conditions to become well-established for the peak months of hurricane season, August - October. It is likely that Atlantic hurricane activity will be suppressed in 2009 due to the strong upper-level winds and resulting wind shear an El Niño event usually brings to the tropical Atlantic.


Figure 3. Sea Surface Temperature (SST) departure from average for the the equatorial Eastern Pacific (the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region"). El Niño conditions exist when the SST in this region rises 0.5°C above average. As of July 8, 2009, SSTs in the Niño 3.4 region had risen to 0.9°C above average. To be considered an "El Niño episode", El Niño conditions must occur for five consecutive months, using 3-month averages. Image credit: Australian Bureau of Meteorology.

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. Wind shear below 12 knots is very conducive for tropical storm formation. High wind shear acts to tear a storm apart. The jet stream's band of strong high-altitude winds is the main source of wind shear in July over the Atlantic hurricane breeding grounds, since the jet is very active and located quite far south this time of year.

The jet stream over the past three months has been locked into a pattern where a southern branch (the subtropical jet stream) brings high wind shear over the Caribbean, and a northern branch (the polar jet stream) brings high wind shear offshore of New England.

The jet stream is forecast to maintain this two-branch pattern for the next week. However, during the final week of July, the subtropical jet is forecast to weaken. This will leave regions of low wind shear over the Caribbean and Gulf of Mexico for the final week of July (Figure 4), increasing the chances of hurricane development.


Figure 4. Wind shear in m/s between 200 mb and 850 mb on July 31, 2009, as forecast by the 00Z July 15, 2009 run of the GFS model. The subtropical jet is forecast to weaken by this time, leaving regions of low wind shear over the Caribbean and Gulf of Mexico for the final week of July. Wind speeds are given in m/s; multiply by two to get a rough conversion to knots. Thus, the red regions of low shear range from 0 - 16 knots.

Dry air and African dust
June and July are the peak months for dust coming off the coast of Africa, and the Saharan dust storms have been quite active over the past month. Expect dust from Africa to be a major deterrent to any storms that try to form between Africa and the Lesser Antilles Islands in July. Several well-developed African waves have been done in by dry air from Africa over the past few weeks.

Steering currents
The steering current pattern over the past few weeks has not changed much. A persistent trough of low pressure has remained entrenched over the Eastern U.S. all summer, bringing cool and relatively moist weather to the eastern half of the country. This trough is strong enough to recurve any tropical storms or hurricanes that might penetrate north of the Caribbean Sea. Steering current patterns are predictable only about 3 - 5 days in the future, although we can make very general forecasts about the pattern as much as two weeks in advance. At present, it appears that the coming two weeks will maintain the strong trough over the Eastern U.S., which decreases the hurricane risk to the U.S. Gulf Coast. There is no telling what might happen to the steering current pattern during the peak months of August, September, and October, but it is often difficult to break a months-long steering current pattern like the current one.

Summary
Recent history suggests a 63% chance of a named storm occurring in the last half of July. Given that none of the computer models are forecasting tropical storm formation in the coming seven days, and SST and wind shear patterns look pretty average, I'll go with a 30% chance of a named storm forming this month. Such a storm would most likely form near the end of the month, when wind shear is expected to decline due to a weakening of the subtropical jet stream. The last time we went this long in the season without a named storm forming was in 2004, when the first storm (Alex) formed on August 1.

I'll have a new post on Friday.

Jeff Masters

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

Sign In or Register Sign In or Register

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 355 - 305

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36Blog Index

344. btwntx08 "ingore him"

Wouldn't trampling be sufficient?
Member Since: Posts: Comments:
um what BLOB?
Member Since: Posts: Comments:
Quoting PORTCHARLOTTE72:
the nation hurricane center just cancelled the remander of the 2009 hurricane season if you were holding tickets you will recieve a voucher for a free 8ounce frosty at your local wendys resturant

I just happen to be a Wendy's executive and operate the Wendy's in NW Florida and S Alabama. Those vouchers may only be redeemed after November 30th. If we have no storms through then, I'll personally buy everyone a Frosty!
Member Since: Posts: Comments:

AOI

AOI


The blob off NOLA is getting a bit bigger with time
Member Since: Posts: Comments:
I see nothing out there that would even warrant a surface low.
Member Since: Posts: Comments:


Sfc Low??
Member Since: July 15, 2008 Posts: 0 Comments: 799
A HIGHLY-AMPLIFIED TROPICAL WAVE IS OVER THE SW NORTH ATLC AND E
CARIBBEAN EXTENDING FROM 24N67W TO 6N68W MOVING W NEAR 20 KT.
VISIBLE SATELLITE IMAGERY SHOWS A WELL-DEFINED AND
HIGHLY-AMPLIFIED INVERTED-V PATTERN IN THE LOW-LEVEL CLOUDS. Can someone please explain this to me.
Member Since: October 9, 2008 Posts: 0 Comments: 8452
347. HadesGodWyvern (Mod)
Japan Meteorological Agency
Tropical Cyclone Advisory #4
TROPICAL DEPRESSION
6:00 AM JST July 16 2009
============================================

Subject: Tropical Depression In Sea East Of The Philippines

At 21:00 PM UTC, Tropical Depression (998 hPa) located at 15.3N 125.9E has sustained winds of 30 knots with gusts of 45 knots. The depression is reported as moving west-northwest at 9 knots.

Dvorak Intensity:

Forecast and Intensity
=======================
24 HRS: 17.2N 124.6E - 40 knots (CAT 1/Tropical Storm)
Member Since: Posts: Comments:
345. IKE
Quoting StSimonsIslandGAGuy:
What tropical blob is there worth keeping an eye on, if any?


Nothing I would lose any sleep over....just interesting to see what happens with the blobs in the EATL.
Member Since: Posts: Comments:
Titusville 40 years ago..


Member Since: Posts: Comments:


New Wave\

Evening folks!
Link
Member Since: July 11, 2006 Posts: 14 Comments: 11477
339. HadesGodWyvern (Mod)
Philippines Atmospherical Geophysical Astronomical Services and Administration

Tropical Storm "ISANG" continues to threaten Eastern Luzon.

Tropical Cyclone Bulletin #5
===================================
At 5:00 AM PhST, Tropical Storm Isang (07W) located at 16.0°N 125.3°E or 225 kms north northeast of Virac, Catanduanes has 10 minute sustained winds of 65 km/h (35 knots) with gustiness of 80 km/h) (45 knots).

Warning Signals
=================

Signal Warning #1 (30-60 kph winds)

Luzon Region
------------
1.Cagayan
2.Isabela
3.Northern Aurora

Additional Information
=======================
Residents living in low-lying areas and near mountain slopes under storm warning signal #1 are alerted against possible flashfloods and landslides.

The public and the disaster coordinating councils concerned are advised to take appropriate actions and watch for the next bulletin to be issued at 11 a.m. today.
Member Since: Posts: Comments:
338. IKE
Quoting BurnedAfterPosting:
Personally with the horrendous track record of the GFS, I would look at the lack of development in the waves as a possible sign that something could spin up lol


I thought about that too. Think I'll keep an eye on this the next few days.



Quoting futuremet:


That moisture seem to be enhanced by the trough. If this system were to be postponed, it will a greater chance of developing, as an upper level anticyclone forms over the region.


Yeah...I see that.
Member Since: Posts: Comments:
Personally with the horrendous track record of the GFS, I would look at the lack of development in the waves as a possible sign that something could spin up lol
Quoting IKE:


It does show a lot of moisture going into SE Florida in a week...



That moisture seem to be enhanced by the trough. If this system were to be postponed, it will a greater chance of developing, as an upper level anticyclone forms over the region.
Member Since: Posts: Comments:
Member Since: Posts: Comments:
Quoting Chicklit:
Beautiful launch.
People lined up and down the beach to watch.
Picture perfect.
Get choked up every time.


And on the eve of Apollo 11's launch too 40 years ago. Never gets old to hear those loud, oppresive engines roar.
Member Since: Posts: Comments:
Beautiful launch.
People lined up and down the beach to watch.
Picture perfect.
Get choked up every time.
Member Since: July 11, 2006 Posts: 14 Comments: 11477
332. IKE
Quoting futuremet:
GFS 18Z Shows nothing


It does show a lot of moisture going into SE Florida in a week...

Member Since: Posts: Comments:


12Z ECMWF shows nothing at the surface, just an open wave.
Member Since: Posts: Comments:
Quoting PORTCHARLOTTE72:
the nation hurricane center just cancelled the remander of the 2009 hurricane season if you were holding tickets you will recieve a voucher for a free 8ounce frosty at your local wendys resturant
lol-I would take a shake over charlie or jeanne..........
Member Since: Posts: Comments:
GFS 18Z Shows nothing
Member Since: Posts: Comments:
Had a good view from Lakeland. Godspeed Endeavour.
Member Since: Posts: Comments:
Member Since: May 21, 2006 Posts: 5095 Comments: 116122
326. IKE
18Z GFS shows a trough split in the GOM off of the trough coming down...Link
Member Since: Posts: Comments:
Quoting PORTCHARLOTTE72:
the nation hurricane center just cancelled the remander of the 2009 hurricane season if you were holding tickets you will recieve a voucher for a free 8ounce frosty at your local wendys resturant


great I love the chocolate frostys where do I get my voucher :)
Member Since: Posts: Comments:
the nation hurricane center just cancelled the remander of the 2009 hurricane season if you were holding tickets you will recieve a voucher for a free 8ounce frosty at your local wendys resturant
Member Since: Posts: Comments:
322. IKE
18Z GFS puts that wave close to the area that map showed by next Tuesday...from eastern Cuba through the eastern Bahamas..........
Member Since: Posts: Comments:
Just like ole Neil and crew did it almost exactly 40 years ago to the day.
Member Since: Posts: Comments:
its amazing thing pat i've watch them all
Member Since: Posts: Comments:
Thank you Mother Nature for cooperating today I know you have no ears or read the blog at least I do not think so, but thank you for finally making the Launch possible:)
Member Since: Posts: Comments:
Welcome to Space Ladies and Gents..
Now 13 Humans are in Earth Orbit,on the Eve of the Apollo 11 Launch 40years ago.

Fantastic..

Member Since: Posts: Comments:
316. IKE
Didn't see it here in the panhandle...saw some ducks flying over....

I did see one launch about 4 am one time.
Member Since: Posts: Comments:
Could barely see it here in Lake Worth...Good luck Endeavour!
Member Since: Posts: Comments:
yup I saw it too, was pretty cool

of course launches are better at night lol
48 hours

72 hours

96 hours

120 hours
Member Since: Posts: Comments:
Lift off was awesome...
Member Since: Posts: Comments:
good luck crew nice launch
Member Since: Posts: Comments:
That was amazing, but how the heck do they store all that fuel?
Member Since: Posts: Comments:


Great picture of some gust fronts.
Member Since: Posts: Comments:
We have lift off.
Member Since: Posts: Comments:
What's up Press? Long time. Hope all is good with Portlight. Great weather here in the beautiful South Carolina Lowcountry. So far so good with hurricane season. Not expecting much this year. I think this persistent troughiness will keep us protected. Doesn't look like any drastic change to the longwave pattern through late summer and into early fall.
Member Since: Posts: Comments:
No development likely next 4 to 6 weeks,if not longer.Conditions unfavorable for tropical storms.high shear,coolwater temps,troughs,dust,el nino,and more.
Member Since: Posts: Comments:
305. IKE
Think I'll head to my dock in a minute and see if I can see the shuttle from over here in the Florida panhandle....
Member Since: Posts: Comments:

Viewing: 355 - 305

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36Blog Index

Top of Page

About

Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather

Local Weather

Overcast
63 °F
Overcast

JeffMasters's Recent Photos

Dunham Lake Sunset
Carrot Nose in Danger
Deep Snow in Brookline, MA
Sunset at Fort DeSoto