Remainder of July hurricane outlook

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

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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

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i think the wave around 40 is under a cloaking device.
Central Atlantic IR
looks like shear will kill it unless it can rise above 20 lat.
shear map goodnight!
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Quoting willdunc79:
wunderkid JMHO I say 20 maybe 25%


I still got a crow on ya..
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Quoting willdunc79:
wunderkid JMHO I say 20 maybe 25%


I say 50% before the end of July... and 100% for August.
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wunderkid JMHO I say 20 maybe 25%
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AOI

AOI

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so what is the probability of a td or ts before the end of july
Member Since: June 13, 2009 Posts: 2 Comments: 12716
Quoting stormwatcherCI:
Who are you refering to with if the shoe fits. I only said sarcasm is uncalled for. Reedzone only mentioned what the models show and I didn't see him comment that he was 100 % behind a specific model. I could say my local weather channel predicts rain tonight but that doesn't say I am 100 % certain it will rain. The models are there just for guidance not to swear by as conditions are constantly changing.
The shoe fits comment wan not meant toward you, it was meant toward the kids making the ludicrous comments.
Member Since: August 15, 2008 Posts: 0 Comments: 2515

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I think we'll have a decent chance of seeing one of the two waves in the catl development once they reach the cen carib. Second looks very healthy, but with a fine amount of dry saharan air ahead of it.
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Quoting Ossqss:
Three headed monster? Could be, but watch the gulf also...... :) and howdy.....

Howdy to you too.
Member Since: October 9, 2008 Posts: 0 Comments: 8436
Quoting atmoaggie:
Yep, having a rough go of it in TN and KY. Trees, highways signs down, semis blown over, and roofs pulled off commercial structures (condition before the storms unknown at Hubs Restaurant).

http://www.spc.noaa.gov/climo/reports/today.html
My sister lives around Lexington, Ky. Do you know if there were any tornadoes in that area ?
Member Since: October 9, 2008 Posts: 0 Comments: 8436
Three headed monster? Could be, but watch the gulf also...... :) and howdy.....

Member Since: June 12, 2005 Posts: 6 Comments: 8188
Yep, having a rough go of it in TN and KY. Trees, highways signs down, semis blown over, and roofs pulled off commercial structures (condition before the storms unknown at Hubs Restaurant).

http://www.spc.noaa.gov/climo/reports/today.html
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Quoting hunkerdown:
The truth hurts, huh...and who says sarcasm is uncalled for. If the shoe fits...
Who are you refering to with if the shoe fits. I only said sarcasm is uncalled for. Reedzone only mentioned what the models show and I didn't see him comment that he was 100 % behind a specific model. I could say my local weather channel predicts rain tonight but that doesn't say I am 100 % certain it will rain. The models are there just for guidance not to swear by as conditions are constantly changing.
Member Since: October 9, 2008 Posts: 0 Comments: 8436
Quoting stormwatcherCI:
Sarcasm is uncalled for.
The truth hurts, huh...and who says sarcasm is uncalled for. If the shoe fits...
Member Since: August 15, 2008 Posts: 0 Comments: 2515
Quoting spinzone:
I see the Doctor's blog is propagated with the usual younger people tonight.

The only perturbation I can see is a developing gale situation off the northern Colombian coast.

Other than that there are no current or forecast lows in the Atlantic Basin.

And you don't even need to go out on a limb to make that statement.
Member Since: August 15, 2008 Posts: 0 Comments: 2515
Quoting hunkerdown:
Then by all means let the models be your guidance. We all know the models have been perfect and spot on so far...
Sarcasm is uncalled for.
Member Since: October 9, 2008 Posts: 0 Comments: 8436
Quoting BurnedAfterPosting:
wow lol I didnt mean to kill the blog lol
Do you think we scared them all off ?
Member Since: August 15, 2008 Posts: 0 Comments: 2515
wow lol I didnt mean to kill the blog lol
Quoting reedzone:



Good point, though I was saying IF there was a system ;) (basically just putting a ghost storm in the picture haha)


well if IFS and BUTS were candy and nuts, we would all have a wonderful christmas lol
Quoting hunkerdown:
Then by all means let the models be your guidance. We all know the models have been perfect and spot on so far...


The only model that has been worth anything this season is the ECMWF, it has been light years ahead of every other model

Even it has missed some too, but it has done fairly well so far.

Quoting hunkerdown:
With the way the models have been, I wouldn't put too much into them. Any track will ultimately depend on the features that are in place at the time. Since conditions are constantly changing, and there isn't even any system to apply the "track" to, I wouldn't worry about it for now.


Good point, though I was saying IF there was a system ;) (basically just putting a ghost storm in the picture haha)
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Quoting HURRICANECAT5:
WHICH IS THE WAVE WITH THE LLC?
the most recent one to come off of the coast 26 west
Member Since: June 13, 2009 Posts: 2 Comments: 12716
Quoting reedzone:
The models show a strong high pressure for the next 144 hours, after that strong trough comes to the East, that would pull a system north, but the high will build west and keep the storm on a NW to NNW coarse, kind of like Isabel (2003). Isabel was influenced by a trough, but the trough weakened and could not recurve it, so the hurricane ran right into it. It just is what it is, the pattern does not favor a recurvature for the next 2 weeks. Weather456 has shown a diagram showing the pattern would be unfavorable for strong troughs and so far, that's been the case.
Then by all means let the models be your guidance. We all know the models have been perfect and spot on so far...
Member Since: August 15, 2008 Posts: 0 Comments: 2515
Quoting reedzone:
The models show a strong high pressure for the next 144 hours, after that strong trough comes to the East, that would pull a system north, but the high will build west and keep the storm on a NW to NNW coarse, kind of like Isabel (2003). Isabel was influenced by a trough, but the trough weakened and could not recurve it, so the hurricane ran right into it. It just is what it is, the pattern does not favor a recurvature for the next 2 weeks. Weather456 has shown a diagram showing the pattern would be unfavorable for strong troughs and so far, that's been the case.


You must have missed all the discussions that are calling for upper 50's in the southeast at the beginning of next week.
Quoting hurricanefiend85:
Hey Reedzone, Appreciate the the forecast. I guess we'll all just have to wait in see. Unfortunately I travel between both South FL and NYC for work purposes. Living mostly in NYC now. It would be sheer hell here if a hurricane were to hit. The wind would obviously be devestating but with a significant storm surge... The big fear is that since most NY'ers have never experienced a storm they would seek shelter in the subways which sometimes flood significantly during thunder storms here, much less with a 15 or 20 foot storm surge rolling in. Not to mention that as the seas rose while the storm approached they would have to close all the tunnels due to the same fear of flooding. Basically in a worst case scenario with a Cat3 or higher storm with significant storm surge...Definitely the costliest storm in history in terms of both money and loss of life. Let's hope that the conditions just never line up for a NY Horrorcane as someone earlier posted. And for that matter, let's hope conditions remain unfavorable up and down the coast!


Lets do hope, and I hope anyone who has seen this forecast does NOT use this for life and death situations, this is all based on evaluations from the pattern.
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Quoting hunkerdown:
With the way the models have been, I wouldn't put too much into them. Any track will ultimately epend on the features that are in place at the time. Since conditions are constantly changing, and there isn't even any system to apply the "track" to, I wouldn't worry about it for now.


Agreed
The models show a strong high pressure for the next 144 hours, after that strong trough comes to the East, that would pull a system north, but the high will build west and keep the storm on a NW to NNW coarse, kind of like Isabel (2003). Isabel was influenced by a trough, but the trough weakened and could not recurve it, so the hurricane ran right into it. It just is what it is, the pattern does not favor a recurvature for the next 2 weeks. Weather456 has shown a diagram showing the pattern would be unfavorable for strong troughs and so far, that's been the case.
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Quoting cyclonekid:
guys and gals...what are you guys thinking about the three tropical waves in the CATL? Do you people think they could emerge into one and become a Carolina Monster (like Isabel) or do you think it will be a problem to the fishies out in the Atlantic?

maybe maybe not and isabel was in september and if it did it would be 5or6 categories down maybe a td or ts
Member Since: June 13, 2009 Posts: 2 Comments: 12716
Quoting reedzone:


Strength doesn't matter, the models have the high in a place where if anything, even a hurricane tracks west, it won't recurve. This is going by the models and the current pattern.
With the way the models have been, I wouldn't put too much into them. Any track will ultimately depend on the features that are in place at the time. Since conditions are constantly changing, and there isn't even any system to apply the "track" to, I wouldn't worry about it for now.
Member Since: August 15, 2008 Posts: 0 Comments: 2515
Hi Cyclone Kid!

1) Are you located in NC or from there?
2) IMHO I think the waves will start off strong and slowly one by one fade out but will serve the purpose of adding moisture to the dry air & help to get some of that dust out of the air but I still don't see anything forming until Aug. I think the 3 waves are doing nothing right now but to slowly help get the atmosphere right & ready for tropical systems in Aug.
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Quoting Ron5244:
I'm going to go out on a limb here and say we're generally in the clear here for this season.


Don't go out too far, that limb looks pretty weak.
Member Since: August 15, 2008 Posts: 0 Comments: 2515
Hey Reedzone, Appreciate the the forecast. I guess we'll all just have to wait in see. Unfortunately I travel between both South FL and NYC for work purposes. Living mostly in NYC now. It would be sheer hell here if a hurricane were to hit. The wind would obviously be devestating but with a significant storm surge... The big fear is that since most NY'ers have never experienced a storm they would seek shelter in the subways which sometimes flood significantly during thunder storms here, much less with a 15 or 20 foot storm surge rolling in. Not to mention that as the seas rose while the storm approached they would have to close all the tunnels due to the same fear of flooding. Basically in a worst case scenario with a Cat3 or higher storm with significant storm surge...Definitely the costliest storm in history in terms of both money and loss of life. Let's hope that the conditions just never line up for a NY Horrorcane as someone earlier posted. And for that matter, let's hope conditions remain unfavorable up and down the coast!
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Quoting BurnedAfterPosting:


I think they arent even close to developing and to give them a possible track is kind of crazy at this point

Whatever eventual strength any of these waves obtain will affect the track in the end, stronger storm will tend to get recurved, if it stays weak it could stay further south


Strength doesn't matter, the models have the high in a place where if anything, even a hurricane tracks west, it won't recurve. This is going by the models and the current pattern.
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I'm going to go out on a limb here and say we're generally in the clear here for this season.


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WHICH IS THE WAVE WITH THE LLC?
Member Since: June 16, 2008 Posts: 0 Comments: 134
Judging by what they look like tonight...Mariner interests.
Member Since: September 10, 2007 Posts: 0 Comments: 11539
Quoting cyclonekid:
guys and gals...what are you guys thinking about the three tropical waves in the CATL? Do you people think they could emerge into one and become a Carolina Monster (like Isabel) or do you think it will be a problem to the fishies out in the Atlantic?


I think they arent even close to developing and to give them a possible track is kind of crazy at this point

Whatever eventual strength any of these waves obtain will affect the track in the end, stronger storm will tend to get curved out to sea, if it stays weak it could stay further south
guys and gals...what are you guys thinking about the three tropical waves in the CATL? Do you people think they could emerge into one and become a Carolina Monster (like Isabel) or do you think it will be a problem to the fishies out in the Atlantic?
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<>a href="http://cimss.ssec.wisc.edu/tropic/real-time/wavetrak/winds/m8split.html "

target="_blank">Link
Member Since: June 13, 2009 Posts: 2 Comments: 12716
Watch that spot in Tennessee show up on SPC in a little while...nevermind, showing up as I type.


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Quoting wunderkidcayman:

around what time
Just give it a name and be done with it.
Member Since: August 15, 2008 Posts: 0 Comments: 2515
even with its moisture field this wave could have to deal with dry air, it will also have to deal with a strong downward pulse of the MJO, which generally surpress convection
Here's my Forecast for August-September if you all missed it earlier..As I've mentioned, the breeding ground might be right off the East Coast with lots of homegrown storms. I can see a few Cape Verde storms form and make it into the Carribean, but with the way things are shaping up, they will probably be weak like (Ingrid, Karen, and Melissa in 2007). I can see lots of storms like Florence (2006) where they get past 60W but you get a strong trough and it recurves the storm away from the USA. I don't see much in the Carribean till October, November. I think there will be some TUTT features there and could suppress any development. So Florida to Maine and Bermuda is my biggest threat for landfalling storms.. At least in August and September. Things can change real quick, but this is what my current thinking is. NYC may want to watch the tropics this year.

Photobucket
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Quoting BurnedAfterPosting:


We will see, but it looks fairly dry out there

fairly dry? in what way
Member Since: June 13, 2009 Posts: 2 Comments: 12716
Im not sure what time
Quoting reedzone:


If convection starts to develop around it, things could get interesting now that we know it's a LLC. I dunno though, so hard to get things going in that area in July.


We will see, but it looks fairly dry out there
Quoting BurnedAfterPosting:
tomorrow morning

around what time
Member Since: June 13, 2009 Posts: 2 Comments: 12716
Quoting BurnedAfterPosting:
yea blue barbs, means its very weak

I wouldnt put much stock in it just yet, we will see what the next QS shows


If convection starts to develop around it, things could get interesting now that we know it's a LLC. I dunno though, so hard to get things going in that area in July.
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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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