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
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 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 — Blog Index
Betsy was my first dance with a Eyewall to be retired. I was 5.7 years old at the time.
i'm sorry but i love the 5.7 years part.
i have realized that no matter how much money you do or dont make you can not control the weather.
and the weather controls everything.
hi pat!
ya left a few things out...
An upper level low pressure system combined with a tropical wave developed a broad trough of low pressure over the central Gulf of Mexico on October 24. A rapid increase in cloudiness and convection led to the formation of a tropical depression on October 26. A high pressure system to its northeast forced it westward, where it became Tropical Storm Juan later on October 26.
At the time and throughout its lifetime, Juan was very disorganized, and resembled a subtropical cyclone with its winds well away from the center. A developing trough brought the storm northward, where it became better organized. Early on October 28, Juan reached hurricane strength, and hours later it reached a peak of 85 mph (140 km/h) winds.
Under the influence of a large scale upper-level low pressure area, Juan executed a cyclonic loop off the Louisiana coast later on October 28. It turned northward, and hit near Morgan City, Louisiana on the morning of October 29. Still under the influence of the low, Juan again looped to the southeast, and weakened to a tropical storm over land on October 29, and emerged into the Gulf of Mexico on October 30 over Vermilion Bay.
Juan paralleled the southern Louisiana coastline and crossed the extreme southeast portion of the state on October 31. Over the open waters of the Gulf, Juan restrengthened to a 70 mph (110 km/h) storm, just before hitting near the Alabama/Florida border that night. Once over land, Juan rapidly weakened, and became extratropical over Tennessee on November 1. Its remnants accelerated northward into Canada by the morning of November 3. Of interest, an upper level low closed off in the wake of Juan, forming a new occluded cyclone, which added to the rainfall totals across Virginia and West Virginia. The combined impact of Juan and the occluded cyclone that formed in its wake led to a flood of record size across West Virginia.
Enhanced convection over the EPAC from the ENSO is part of the problem, but the downward phase of the MJO is a big problem as well. You noticed the above average SLP anomalies over the MDR/equatorial Atlantic, precipitation and OLR anomalies are also showing up over the region. Downward motion, or a lack of instability over the area are responsible for this. Looking at velocity potential at 200hPa it becomes quite evident that air has been converging aloft over the equatorial Atlantic and MDR region. This explains the higher SLPs, lack of precipitation, and OLR anomalies over the area.
So the question is then what is causing this anomaly. The ENSO can obviously be partially blamed, however, if we look over the East Pacific upward motion over the region actually hasn't been to impressive over the last month, especially over the central pacific (nino regions 3, 3.4, and 4). Instead, the majority of the upward motion has been focused over Africa. Not surprisingly, the MJO has been hanging out over the African continent and Indian Ocean region (see phase diagram below). So while the anomalous warming in the EPAC (not really the CPAC) is partially to blame (ENSO related warming), the MJO is also a clear and significant problem.
200hPa velocity potential anomalies, notice the lack of significant upward motion over the EPAC or CPAC, and more significant upward motion over Africa.
MJO phase diagram
GFS also forecasting the majority of the upward motion to remain over Africa for the next two weeks.
Its vector had changed from 17.8mph(28.7km/h) West West to 16.7mph(27km/h) West
MaxSusWinds had decreased from 45knots(52mph)83km/h to 40knots(46mph)74km/h
And minimum pressure had increased from 997millibars to 1000millibars
For those who like to visually track TS.Emilia's path...
HPV is Hanalei,Kauai :: HNL is Honolulu,Oahu :: OGG is Kahalui,Maui :: ITO is Hilo,Hawaii
The kinked line represents the 1st day of TS.Emilia's path after it became a TropicalStorm again
Easternmost dot on the longest line is TS.Emilia's most recent position
The longest line is a straightline projection through TS.Emilia's 2 most recent positions to its closest approach to Hawaii (The 3 previous endpoints are on the blob south of the straightline)
14July6amGMT: TS.Emilia had been headed toward passing 343miles(552kilometres)South of Hawaii
14July12pmGMT: TS.Emilia had been headed toward passing 332miles(534kilometres)South of Hawaii
14July6pmGMT: TS.Emilia had been headed toward passing 322miles(519kilometres)South of Hawaii
15July12amGMT: TS.Emilia was heading toward passing 105miles(169kilometres) South of Hawaii
in ~3days11hours from now
Copy&paste hpv, hnl, 13.96n155.063w, 14.114n155.112w, 14.25n155.154w, ogg, ito,15.3n124.2w- 15.5n125.4w- 15.5n126.7w- 15.5n127.9w- 15.5n129.3w, 15.5n129.3w-15.5n130.6w, 15.5n130.6w-15.5n132.2w, 15.5n132.2w-15.7n133.7w, 15.5n132.2w-17.382n155.718w, 18.911n155.681w-17.382n155.718w into the GreatCircleMapper for more information
The previous mapping for comparison
Multi Model MJO Phase Diagram
are ya being positive???
Not that it will matter much soon.
how often are they open??
That means no new Kelvin Wave that transports the warm waters from west to east delaying El Nino prospects?
It'll be a few weeks, probably not until mid-August.
well it was nic why it lasted
guss oh may be back guys
14 ts, 1 td, 5 H1, 4 H2, 3 H3, 1 H4
A few other notables:
The storm no one remembers from 1957 (for obvious reasons)
Some majors
is that all you no how too post?
Maybe. We'll have to watch off the East Coast for frontal storms and in the East Atlantic by early August for tropical development.
taz are ya going to be on the pch with cantore looking for fabio???
lol nop i be at home
I'm expecting the two months to be quite busy, yes. We should expect at least 9 more named storms this season.
did ya get ya new comp??
i i still have my 19" 720p TV its all so a emerson
nop
see post 1585
Either way, all of the ingredients have to pretty much gel at the same time to favor formation. While the recent waves passing across Florida and into the Gulf were in the right place (low sheer and warm waters), the large scale synoptic pattern in place over the Gulf region, and particularly the large ULL in the Central Gulf north of the Yucatan Peninsula, prevented any significant development; they came through at the wrong time.
Three in August, four in September, and two between October and November.
what's your thoughts with fabio??
i will have to make a road trip and check it out..
it sould start too weak in tonight
1957 was a bad yr for swla
Yes it was. :(
Viewing: 1551 - 1601
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 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 — Blog Index