July Atlantic hurricane outlook
It's mid-July, and we have yet to see a named storm form in the Atlantic this month. The computer models are not predicting any development through at least July 20, and if we make it all the way to the end of the month without a named storm forming, it will be the first July since 2009 without a named storm. Since the current active hurricane period began in 1995, 13 of 17 years (76%) have had a named storm form during July. The busiest July occurred in 2005, when five named storms and two major hurricanes formed. These included Hurricane Dennis and Hurricane Emily--the strongest hurricanes ever observed so early in the season. Only eight major hurricanes have formed in July since record keeping began in 1851. As seen in Figure 1, most of the last half of July activity occurs in the Gulf of Mexico and waters off the Southeast U.S. coast. These type of storms form when a cold front moves off the U.S. coast and stalls out, with the old frontal boundary serving as a focal point for development of a tropical disturbance (as happened for Alberto, Beryl, Chris, and Debby in 2012.) There will be at least two cold fronts moving off the U.S. Mid-Atlantic coast over the next two weeks. The first of these fronts will push offshore around July 20, and we will need to watch the waters offshore of North Carolina for development then. Formation potential will be aided by ocean temperatures that are about 0.7°C (1°F) above average along the U.S. East Coast.
Figure 1. Tracks of all tropical storms and hurricanes 1851 - 2006 that formed July 16-31. The U.S. coast from North to Texas are the preferred strike locations. Only a few storms have formed in the tropical Atlantic and Caribbean in July. Wind shear is typically too high and SSTs too cool in July to allow African waves in the Caribbean and tropical Atlantic to develop into tropical storms. However, a few long-track "Cape Verdes" hurricanes have occurred in July, spawned by tropical waves that came off the coast of Africa. African tropical waves serve as the instigators of about 85% of all major hurricanes.
Figure 2. The seasonal distribution of Atlantic hurricane activity shows that July typically has low activity. Image credit: NHC.
Sea Surface Temperatures: slightly above average
The departure of Sea Surface Temperatures (SST) from average over the tropical Atlantic between Africa and Central America was about 0.3°C above average during June (Figure 3.) This figure has not changed much over the first two weeks of July. These temperatures are not warm enough to appreciably affect the odds of a July named storm or hurricane. The strength of the Azores-Bermuda high has been near average over the past two weeks, driving near-average trade winds. The latest 2-week run of the GFS model predicts continued average-strength trade winds through late-July, so SSTs should remain about 0.3°C above average during this period, due to average amounts of cold water mixing up from below due to the wind action on the water.
Figure 3. Sea Surface Temperature (SST) departure from average for July 12, 2012. SSTs were 0.3°C above 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 on the way?
For two consecutive weeks, ocean temperatures 0.5 - 0.6°C above average have been present in the tropical Eastern Pacific, which is right at the threshold for a weak El Niño episode. NOAA's Climate Prediction Center has issued an El Niño Watch, and gives a 61% chance that El Niño conditions will be present during the August - September - October peak of the Atlantic hurricane season. The likely development of a full-fledged El Niño episode means that Atlantic hurricane activity will probably be suppressed in 2012, due to the strong upper-level winds and high wind shear these events typically bring to the tropical Atlantic.
Figure 4. 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 9, 2012, SSTs in the Niño 3.4 region had risen to 0.5°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: NOAA Climate Prediction Center.
Wind shear: above average
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 has two bands of strong high-altitude winds that are currently bringing high wind shear to the Atlantic. The southern branch (subtropical jet stream) is bringing high wind shear to the Caribbean, and the northern branch (polar jet stream) is bringing high wind shear to the waters offshore of New England. This configuration often leaves a "hole" of low shear between the two branches, off the Southeast U.S. coast and over the Gulf of Mexico. The jet stream is forecast to maintain this two-branch pattern over the coming two weeks. Wind shear has been about 10 - 20% higher than average over the first two weeks of July, and is predicted to be mostly above average for the coming two weeks. This will cut down on the odds of a July storm.
Figure 5. Vertical instability over the Caribbean Sea in 2012 (blue line) compared to average (black line.) The instability is plotted in °C, as a difference in temperature from near the surface to the upper atmosphere. Thunderstorms grow much more readily when vertical instability is high. Instability has been lower than average, due to an unusual amount of dry air in the atmosphere, reducing the potential for tropical storm formation. Image credit: NOAA/NESDIS/CIRA.
Dry air: above average
As seen in Figure 5, there has been an unusual amount of dry, stable air in the Caribbean this year creating low levels of vertical instability. This has occurred due to a combination of dry air from Africa, and upper-atmosphere dynamics creating large areas of sinking air that dry as they warm and approach the surface. The Gulf of Mexico and tropical Atlantic between the coast of Africa and the Lesser Antilles have also seen low vertical instability this summer. June and July are the peak months for dry air and dust coming off the coast of Africa, and the Saharan dust storms have been quite active over the past two weeks. Expect dry air to be a major deterrent to any storms that try to form in the tropical Atlantic during July.
Steering currents: average
The predicted steering current pattern for the next two weeks is a typical one for July. We have an active jet stream bringing many troughs of low pressure off the East Coast of the U.S. These troughs are frequent enough and 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. There is no telling what might happen during the peak months of August, September, and October--we might be in for a repeat of the favorable 2010 and 2011 steering current pattern, which recurved most storms out to sea--or the unfavorable 2008 pattern, which steered Ike and Gustav into the Gulf of Mexico.
Summary: a below average chance of a July tropical storm
Given that none of the computer models are forecasting tropical storm formation in the coming seven days, SSTs are only slightly above average, and wind shear and vertical stability are above average, I'll go with a 30% chance of a named storm forming in the Atlantic during the remainder of July.
Figure 6. Hurricane Emilia over the Eastern Pacific at 20:35 UTC July 10, 2012. At the time, Emilia was a Category 3 hurricane with 125 mph winds. Emilia peaked earlier in the day as a Category 4 storm with 140 mph winds--the strongest hurricane in the East Pacific so far in 2012. Image credit: NASA.
An active Eastern Pacific hurricane season
It's been a very active start to the Eastern Pacific hurricane season, where we've already had six named storms, four hurricanes, and three intense hurricanes. A typical season has 4 named storms, 2 hurricanes, and 0 intense hurricanes by July 14. The formation of Tropical Storm Fabio on July 12 marks the 4th earliest formation of the Eastern Pacific's season's sixth storm. The record is held by the year 1985, when the season's sixth storm formed on July 2. Record keeping began in 1949.
Have a great weekend, everyone, and I'll be back Monday with a new post.
Jeff Masters
Reader Comments
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you wouldnt expect the NHC to go higher would you?
maybe its because whenever guidance says something, buoys, ships, and sometimes recon tend to show lower winds.
.DAY ONE...TODAY AND TONIGHT
SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DEVELOP TODAY.
WIDESPREAD PRECIPITATION IS NOT EXPECTED AND RAINFALL AMOUNTS ARE
EXPECTED TO BE LESS THAN THE PAST FEW DAYS. AVERAGE RAINFALL IS
EXPECTED TO BE A HALF INCH OR LESS WITH SOME ISOLATED TOTALS
BETWEEN 1 AND 2 INCHES IN THE STRONGER STORMS.
I agree, not only by the totals we have dumped out but even their updates on their homepage have different totals different days. Maybe I am looking at it wrong but they should check it out. Thanks for letting me know about that page. Are you in the Houston area?
i see u wont give up...2nd week of august i tell you.
That 1014 subtropical low wont be another chris.
july 8 + 6.52
july9 +5.05
july 10 +6.46
july 11 +12.25
july 12 +18.22
july 13 +15.82
july 14 +8.92
And Today preliminar values July 15 +20.50
Clearly El nino is delayed for now.
Link
NATIONAL WEATHER SERVICE MIAMI FL
923 AM EDT SUN JUL 15 2012
UPPER TROUGH BETWEEN THE 2 LOWS TO THE NE AND SW RESPECTIVELY MOVING
NW ACROSS THE S FLA AT THE MOMENT. UNDER MOSTLY CLOUDY SKIES...RADAR
DETECTS WIDESPREAD SHOWERS OVER THE ATLC AND THE SE GULF OE MEX WITH
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS DEVELOPING OVER THE E
COAST ZONES. THE WIDESPREAD CONVECTIVE ACTIVITY EXPECTED TO REMAIN
OFFSHORE WITH MAINLY AFTERNOON AND EARLY EVENING ACTIVITY OVER THE
MAINLAND. NOT AN ALL DAY RAIN OUT BUT WILL KEEP POPS AS IS IN THE
CURRENT FORECAST AS ALL AREAS HAVE A LIKELY CHANCE OF SEEING SOME
RAINFALL TODAY.
The models are pretty good at honing in on which ones might develop. No one knows the time and hour when they will start developing in the Central-Atlantic but we should start seeing model consensus on possible development in the coming 3-6 week period.
ok croweater
A delayed El Nino if the MJO continues in the Indian Ocean.
it was possible to have a weak one by now, but i didnt count on it.
I dont trust those forecasts to be on time
5 years after
10 years later
Only the first 1:30 is actually credible, after that it's all hollywood crap.
You will have to copy and paste the link as it wont let me embed the code over.
http://www.youtube.com/watch?v=JwfCRAtkYEI&featur e=channel&list=UL
And some data from this latest solar flare event:
who is he that you should hate him so much?
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE WARNING//
REF/A/JOINT TYPHOON WRNCEN PEARL HARBOR HI/150421Z JUL 12//
AMPN/TROPICAL CYCLONE FORMATION ALERT//
RMKS/
1. TROPICAL DEPRESSION 08W (EIGHT) WARNING NR 001
01 ACTIVE TROPICAL CYCLONE IN NORTHWESTPAC
MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
WIND RADII VALID OVER OPEN WATER ONLY
---
WARNING POSITION:
151200Z --- NEAR 22.4N 140.1E
MOVEMENT PAST SIX HOURS - 300 DEGREES AT 13 KTS
POSITION ACCURATE TO WITHIN 060 NM
POSITION BASED ON CENTER LOCATED BY A COMBINATION OF
SATELLITE AND SYNOPTIC DATA
PRESENT WIND DISTRIBUTION:
MAX SUSTAINED WINDS - 025 KT, GUSTS 035 KT
WIND RADII VALID OVER OPEN WATER ONLY
REPEAT POSIT: 22.4N 140.1E
---
FORECASTS:
12 HRS, VALID AT:
160000Z --- 23.9N 137.3E
MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT
WIND RADII VALID OVER OPEN WATER ONLY
VECTOR TO 24 HR POSIT: 295 DEG/ 15 KTS
---
24 HRS, VALID AT:
161200Z --- 25.2N 134.3E
MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
WIND RADII VALID OVER OPEN WATER ONLY
VECTOR TO 36 HR POSIT: 300 DEG/ 17 KTS
---
36 HRS, VALID AT:
170000Z --- 26.9N 131.1E
MAX SUSTAINED WINDS - 040 KT, GUSTS 050 KT
WIND RADII VALID OVER OPEN WATER ONLY
RADIUS OF 034 KT WINDS - 060 NM NORTHEAST QUADRANT
055 NM SOUTHEAST QUADRANT
055 NM SOUTHWEST QUADRANT
060 NM NORTHWEST QUADRANT
VECTOR TO 48 HR POSIT: 315 DEG/ 17 KTS
---
EXTENDED OUTLOOK:
48 HRS, VALID AT:
171200Z --- 29.3N 128.3E
MAX SUSTAINED WINDS - 040 KT, GUSTS 050 KT
WIND RADII VALID OVER OPEN WATER ONLY
RADIUS OF 034 KT WINDS - 060 NM NORTHEAST QUADRANT
055 NM SOUTHEAST QUADRANT
055 NM SOUTHWEST QUADRANT
060 NM NORTHWEST QUADRANT
VECTOR TO 72 HR POSIT: 350 DEG/ 17 KTS
---
72 HRS, VALID AT:
181200Z --- 36.0N 126.9E
MAX SUSTAINED WINDS - 020 KT, GUSTS 030 KT
WIND RADII VALID OVER OPEN WATER ONLY
DISSIPATED AS A SIGNIFICANT TROPICAL CYCLONE OVER LAND
---
REMARKS:
151500Z POSITION NEAR 22.8N 139.4E.
TROPICAL DEPRESSION 08W, LOCATED APPROXIMATELY 165 NM SOUTH-
SOUTHWEST OF IWO TO, JAPAN, HAS TRACKED WEST-NORTHWESTWARD AT 13
KNOTS OVER THE PAST SIX HOURS. THIS WARNING SUPERSEDES AND CANCELS
REF A, JOINT TYPHOON WRNCEN PEARL HARBOR HI 150421Z JUL 12 TROPICAL
CYCLONE FORMATION ALERT (WTPN21 PGTW 150430). MAXIMUM SIGNIFICANT
WAVE HEIGHT AT 151200Z IS 10 FEET. NEXT WARNINGS AT 152100Z,
160300Z, 160900Z AND 161500Z.//
NNNN
Hurrihistory it won't likely develop thanks to dry air at the moment.
i didnt insult you did i?
Do you have a loop of that?
Loudon NH
This Afternoon A slight chance of showers and thunderstorms after 3pm. Partly sunny, with a high near 89. South wind 5 to 7 mph. Chance of precipitation is 20%.
Sorry if this is off topic
89F is quite cool
Big SAL above the train = waves die if they go north
and more coming off
but cool for nascar
There is turning of the clouds on both the one just emerging as the one behind. They have to remain south of 15N to avoid the thick sal.
Viewing: 1801 - 1851
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