Remainder of July hurricane outlook
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
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that has to be the strangest looking cyclone I've ever seen.
As well as possibly killing or damaging hundreds of species and habitats that are very sensitive to temperature change.
Good Morning Folks.............Nothing to Add............
Quite true... specially inhibiting/modifying Plankton development in many areas. :(
I see the high building in over the CATL..you can see it nosing down into the islands..Link...also see the SAL on visible over eastern Cuba, Jamaica and the rest of the islands.
The high is forecast to build in all the way to Florida from the east over the next week. That should keep the waves moving W to WNW.
Interesting to see what happens...
That would mean it would keep the waves away from Florida..correct?
Should bring them heading toward Florida.... from what I've read.
OK...thanks. I'm a little confused though. I thought the high (ridges?) protected what they were over.
Waves will ride the southern end of the high....
Gotcha...thanks 8-)
Link
what ???
AOI
AOI
Pacific
Its not even a tropical storm anymore in my opinion. No deep convection.
Had a feeling yesterday it would do this. Had that Hurricane Noel (2007) type look before he went extra tropical.
LOL... very slow blog today...
Thanks for the link.
Is there a possible low at 6N/33W ?
It'll pick up. Folks have to get to their boring jobs and then they'll all come on here to pass the time....
Link
maybe
A noticeable change in the weather in Tobago this a.m.
A groundswell building on the reef, (first since Easter), tall cloud to the north/west making for much higher humidity than recently.
Feels like rain to me..
Watch it now, as you would have seen it on July 16, 1969, at 9:26 AM EDT. T-minus 00:5:59 and counting.
So, in conclusion, I expect no tropical cyclone development from these two tropical waves or anywhere else through Sunday. From Monday and beyond of next week, the area off of the US Southeast coast will need to be watched closely for signs of development thanks to the trough split and its interaction with those two tropical waves.
FROM Crown Weather
also the pic from the CMC that futuremet showed on the previous page, I cannot find that anywhere
I am looking at all 3 models and neither of them show anything special around that time frame. So what am I missing?
You must be using the same ones I am... I see Nada?
If it wasn't for the fact the British Open was on.... I would be bored silly this morning.
UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 7.2.3
Tropical Cyclone Intensity Algorithm
----- Current Analysis -----
Date : 16 JUL 2009 Time : 130000 UTC
Lat : 17:35:54 N Lon : 124:20:23 E
CI# /Pressure/ Vmax
3.1 / 989.6mb/ 47.0kt
Final T# Adj T# Raw T#
(3hr avg)
3.1 3.1 3.2
Latitude bias adjustment to MSLP : +0.0mb
Center Temp : -82.4C Cloud Region Temp : -73.7C
Scene Type : UNIFORM CDO CLOUD REGION
Positioning Method : FORECAST INTERPOLATION
Ocean Basin : WEST PACIFIC
Dvorak CI > MSLP Conversion Used : PACIFIC
Tno/CI Rules : Constraint Limits : 0.7T/6hr
Weakening Flag : OFF
Rapid Dissipation Flag : OFF
ONE REMAINING UNCERTAINTY
THAT BECOMES INCREASINGLY EVIDENT DAYS 5-7 IS THE WESTWARD
EXPANSION OF THE CENTRAL ATLANTIC UPPER HIGH...WHICH THE MODELS
SUGGEST MAY BRIDGE WITH THE UPPER HIGH OVER THE
SOUTHWEST...ESSENTIALLY PINCHING OFF A PORTION OF THE EASTERN U.S.
TROUGH OVER THE DEEP SOUTH/GULF OF MEXICO/E. TEXAS. THE GFS AND
ITS ENSEMBLE MEAN SHOW THE UPPER HIGH EXPANDING INTO THE SOUTHEAST
FASTER THAN THE ECMWF...WHICH IF TRUE...WOULD SUPPORT MORE
WESTWARD DEVELOPMENT OF THE CUTOFF LOW.
Basically, they are seeing the same pattern as I see next week in that a trof split of sorts will occur causing energy to split off and retrograde. This retrogradition of the UL low will allow for ventilation for any tropical waves tracking towards the Bahamas/SE US creating a more favorable enviornment and the possibility for development.
fingers crossed!!
You can find FM model here: Link
Africa NEXSAT Satellite
Cyclonic turning in a wave is a positive for possible development, but it is rare for a storm to spin up right off the coast of Africa. Usually they have to get a ways off the coast (1-2 days) before they stand a chance. All tropical waves should be monitored, and even more so if they are in a favorable environment and/or it is a climologically ripe time for them to pop. Right now, its still a bit early for a CV wave to pop in EATL, they generally have to get further west into the Caribbean before taking off due to SAL and upper air trends.
That all said, the waves that just came off Africa do bear watching, but I personally don't think they are worth focusing on right now.
The models are putting it on the same track as hurricane Floyd. I scarcely remember hurricane floyd. I do know though that it scared the crap out of florida before it made the jog north.
Apollo 11 lift-off anniversary
Thursday, 16 July 2009 12:25
Apollo 11 was the first manned space mission to land on the Moon. It was the fifth human spaceflight of Project Apollo and the third human voyage to the Moon.
Launched on 16 July 1969, it carried Mission Commander Neil Alden Armstrong, Command Module Pilot Michael Collins and Lunar Module Pilot Edwin Eugene 'Buzz' Aldrin Jr. On 20 July, Armstrong and Aldrin became the first humans to walk on the Moon, while Collins orbited above.
The mission fulfilled President John F Kennedy's goal of reaching the moon by the end of the 1960s...
Link
LIES!
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