An active Atlantic hurricane period coming
The remnants of Tropical Depression Five are no longer a threat, done in by high wind shear and close proximity to land. However, an active period for Atlantic hurricanes is likely for the remainder of August, as the global atmosphere undergoes a major change to the circulation pattern that has dominated Northern Hemisphere weather during July and August. A large trough of low pressure is gathering strength over Europe, and is expected to push eastward. By Thursday, this trough should be able to push away the blocking ridge of high pressure that has given Russia its worst heat wave in history. The shift in circulation has already weakened the large region of sinking air that has brought dry, stable conditions to the tropical Atlantic over the past month. Vertical instability, which was unusually low since late July, has now returned to near normal levels over the tropical Atlantic (Figure 1), though it remains quite low over the rest of the North Atlantic. Instability is measured as the difference in temperature between the surface and the top of the troposphere (the highest altitude that thunderstorm tops can penetrate to.) If the surface is very warm and the top of the troposphere is cold, an unstable atmosphere results, which helps to enhance thunderstorm updrafts and promotes hurricane development. Since SSTs in the Atlantic were at record highs and upper tropospheric temperatures were several degrees cooler than average in July, enhancing instability, something else must have been going on to reduce instability. Dry air can act to reduce instability, and it appears that an unusually dry atmosphere, due to large-scale sinking over the Atlantic, was responsible for the lack of instability. Now that vertical instability has returned to near normal levels, Atlantic hurricane activity should increase to at least average levels over the next two weeks. This is particularly true since SSTs are at record highs and vertical wind shear is at average to below average levels over the tropical Atlantic.
Figure 1. Vertical instability (in °C) over the Caribbean (left) and tropical Atlantic between the Lesser Antilles Islands and coast of Africa (right) in 2010. Normal instability is the black line, and this year's instability levels are in blue. The atmosphere became much more stable than normal in both regions at the end of July. This lack of instability also extended to the Gulf of Mexico and North Atlantic Ocean between Europe and North America. However, in the past few days, vertical instability has returned to normal, thanks to a major pattern shift in the global atmosphere. Image credit: NOAA/CIRA.
Figure 2. The climatology of Atlantic hurricane activity shows a sharp rise in activity around August 18.
Analysis
August 18 historically marks the point where Atlantic hurricane activity makes a major spike upwards (Figure 2.) On average, we can expect to see two named storms and one hurricane during the last half of August. The last half of August usually sees a moistening of the atmosphere off the coast of Africa, as the the African monsoon kicks into high gear. This year is no exception (Figure 3.) The dry Saharan Air Layer (SAL) has retreated to the north, leaving a moist atmosphere conducive for tropical cyclone development off the coast of Africa.
It would not be a surprise to see atmospheric instability increase to above-average levels by early next week as the major atmospheric pattern shift progresses. Will this usher in a hyperactive period of Atlantic hurricane activity next week, with a parade of three or four simultaneous storms strung out across the Atlantic? Probably not, since the Madden-Julian Oscillation (MJO) only marginally favors upward motion over the tropical Atlantic, and is not forecast to change much over the next ten days. The Madden-Julian oscillation is a pattern of enhanced rainfall that travels along the Equator from west to east. The pattern has a wet phase with large-scale rising air and enhanced thunderstorm activity, followed by a dry phase with large-scale sinking air and suppressed thunderstorm activity. Each cycle lasts approximately 30 - 60 days. When the Madden-Julian oscillation is in its wet phase over a hurricane-prone region, the chances for tropical storm activity are greatly increased. The bottom line: I expect we will see 2 - 3 named storms in the Atlantic by the end of August, including one hurricane. Where these storms might develop and move is difficult to say. It currently appears that the global shift in circulation will bring near-average steering currents to the Atlantic over the next ten days, with a series of troughs of low pressure capable of recurving hurricanes, moving across the Atlantic. The GFS model is indicating, though, that during the few days of August, these troughs may weaken, making recurvature of hurricanes less likely, and increasing the probability of landfalling storms.
The GFS, NOGAPS, and ECMWF currently predict that one or two tropical storms will form between Africa and the Lesser Antilles Islands during the period 4 - 10 days from now. The NOGAPS model is predicting the development of a strong tropical disturbance near the coast of Honduras late this week.
Figure 3. Saharan Air Layer (SAL) analysis shows that the dry air and dust of the SAL (orange colors) lies well to the north of the hurricane breeding grounds off the coast of Africa, near the Cape Verdes Islands. Image credit: University of Wisconsin/NOAA Hurricane Research Division.
Smoke bedeviling Moscow again
Light easterly winds over the past few hours have brought smoke from wildfires back into Moscow today. Temperatures at Moscow's Domodedovo airport hit 29°C (84°F) today, which is 11°C (20°F) above average. The latest forecast for Moscow predicts that just one more day remains for Russia's greatest heat wave in recorded history. On Thursday, a strong trough of low pressure will move through European Russia, finally bringing below average temperatures.
Jeff Masters
Reader Comments
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LOL!
Have a good one, Aqua.
Yes I know...you are 100% right. But its a bit scary to see models point at you most of the time.
It worked for me...I just tried it.
Morning Dfly. Should of been over here last night we had off and on for 6 hours of thunder and lightning last night. got almost 3 inches of rain. z-hills fl.
http://www.met.nps.edu/~mtmontgo/storms2010.html
select one, then read the synopses, they discuss a strange jump in the models and have some intelligent guesses as to the causes. I found it interesting...
No telling what mischief will abound on the blog today.
I was shooting that storm from the east side here in O-town.. Got a few good shots. Especially late when the storm settled a bit. I wish I was on the west side of it.. Sure does figure 3 days late huh.. LOL
Atchafalaya Basin hasn't seen rain like this in a while.
My pleasure. Good morning Storm, Ike, Earthdragonfly, etc al
I'm thinkin' in about two weeks things will be much different...
Yup and we should expect more rain today! My lake in the backyard isnt dealin well with all this rain!
Good morning Storm!
Cloudy and cooler here, rain on the way - huzzah!
LONG TERM (FRIDAY NIGHT THROUGH NEXT WEDNESDAY)...BOTH THE 12Z
ECMWF AND THE 00Z GFS INDICATE AN AMPLIFYING TROUGH ALONG THE
EASTERN SEABOARD WITH AN UPPER LOW CLOSING OFF OVER OR JUST SOUTH OF
NEW ENGLAND EARLY NEXT WEEK. BOTH MODELS ALSO SHOW A SURFACE LOW
DEVELOPING EAST OF THE MID ATLANTIC STATES DURING THE TIME.
HOWEVER...THE EURO SHOWS THE STACKED LOW PRESSURE SYSTEM
RETROGRADING AND MOVING ONSHORE OVER THE DELMARVA PENINSULA BY LATE
WEDNESDAY. THE GFS SOLUTION TRACKS BOTH SURFACE AND UPPER LOW OUT
INTO THE OPEN ATLANTIC. EITHER WAY...BOTH SOLUTIONS DRIVE A SURFACE
FRONT DOWN INTO OUR CWA. THE GFS DEVELOPS A WAVE ON THE FRONT IN THE
FLORIDA PANHANDLE LATE IN THE WEEKEND AND SLOWLY DRIFTS SOUTH THEN
WEST EARLY NEXT WEEK. THIS COUPLED WITH DEEP LAYER MOISTURE...
DAYTIME HEATING AND DECENT SHORT WAVE ENERGY OVER THE REGION WILL
KEEP US IN AN UNSETTLED WEATHER PATTERN. LOOK FOR ABOVE SEASONAL
CHANCES FOR SHOWERS AND THUNDERSTORMS EACH DAY. TEMPERATURES WILL BE
AT OR JUST UNDER CLIMO.
Another FISH storm?
Wow... wont be any fish storms with that set up! Dangerous...
thanks Aqua -- won't scroll back that far -- that stuff doesn't go well w/ cafe'
Interesting thoughts on the models (Cot!) I was convinced earlier in season we would be very active, past two weeks - not so....... now I'm wavering...
It is fun to watch Ma Nature Play with our Heads
I'd give it a 55% chance of curving from Bermuda, eastward.
Maybe it will make another loop back to GA and the GOM... LOL!
We only got 1 inch of rain.. drizzle, just drizzle
http://www.esl.lsu.edu/webpics/goes/Storm/Tropics/latest_wv.jpg
whoaaaa - howz the levees???
Believe it or not, it's taken from my Nexus One (Google) phone. I'm also writing from ATM. Uploaded via photobucket.
Agree. Models had it hitting FL, NC, then NYC and now back out to sea. Models all over the place. I dare someone to say fish storm! Lol
Hope them levee's don't break, cuz...when the levee breaks, momma you got to move...Link
amazing!- nice lens.
ahhh - so happy to live in this Paradise - even w/Canes
It's living with OIL in the Gulf that taints the picture of bliss
Sure thing!
K lads be back later... Have a great morning.
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT WED AUG 18 2010
FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...
CLOUDINESS AND SHOWERS OVER THE WEST CENTRAL CARIBBEAN ARE
ASSOCIATED WITH A TROPICAL WAVE MOVING WESTWARD AT 15 MPH. THERE
ARE NO SIGNS OF DEVELOPMENT AND THERE IS A LOW CHANCE...10
PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE
NEXT 48 HOURS.
ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.
$$
FORECASTER CANGIALOSI/KIMBERLAIN
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