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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Not yet LOL. I live in Jax and been around the block too long to believe a particular run. That model run is still way out in the long range.
However, I do note the trend of that CV cyclone going farther west with each run. So, at least in the preliminary runs that the Ridge is going to be building in and increasing the likelihood of preventing re-curvature.
Oh I doubt this is a ghost storm. Its bound to happen anyways. A ghost track is more like it.
Oh I agree Miami.....just saying now everyone will have some weather to talk about and maybe not be so critical of each other. I love the forecast models but they are like using a dart board at that far time out...BTW...thanks to all who actually educate poeple on here...especially educate me!!
LOL
Lets get some ducks in the pond first.
So we're pretty confident we'll see some SWly movement before this system starts to develop?
Still concur... I'm for sure looking for 12Z ECMWF to see if it also buys into such negative dip in the NAO.
I meant that this wont be an out to sea scenario..A US hit is coming more into the picture
I saw that too
Yep he sure did call it!
Pretty impressive AEW. Has an evident mid-level circulation and very well defined inverted V structure. Also got a good moisture field associated with it.
I remember Richmond got hit pretty hard with flooding. I was living in Jax at the time and it was total panic. Boy did we luck out, again.
Not surprising. GFS has been suggesting a very deep low pressure system and trough across Europe. Naturally that would cause pressures to rise significantly across the North Atlantic thus allowing for such a strong negative NAO.
Correct. PG130L put a big dent in the SAL for PG131L to develop to boot.
Already has a fair amount of 850 mb vorticity with the system.
Whats the yellow sitting off the coast of Carolina? What does that mean?
I didn't lump everyone in. :) I said there are plenty of people who would. Plenty implies some number who wouldn't.
WORD OF CAUTION!
I don't usually initiate a pouch that is developing in the
horizontal shear zone in the middle of the Atlantic; however,
the models not only develop a pouch that interacts with nearby
PGI30L, but also ends up more intense than PGI30L.
Although PGI31L is intense at the end of the forecast in most
models, it is not at analysis, and determining its initial
position is troublesome. THERE IS A HIGH AMOUNT OF UNCERTAINTY
IN THE FIRST 24 HOURS FOR THE POSITIONS. Essentially, a large
circulation ~35W is apparent in the analysis. I did position
PGI31L in that large circulation in GFS; however, it becomes
fairly apparent that while that large circulation actually
weakens and creeps westward, a cyclonic area to the east is what
develops. So, some of the models appear to jump to the east for
that reason. (In hindsight, I probably should have initiated
PGI31L farther east.)
That being said, the models (except NOGAPS) do indicate a bit of
eastward motion in the beginning during a Fujiwhara with PGI30L,
followed by westward motion. For that reason, I simply used a
PHASE SPEED OF ZERO m/s.
Read post 318.
It would appear to be PGI31L very close to 30L.
I was writing my post as you put that one up. :)
During the duration of the CV storm, GFS doesn't seem to generate anything else of significance.
I for one would like to know that someone somewhere is keeping the data on X-05...if it were a major and it had done this loopty loop and pop out only to wreak havoc again, maybe some data would flag the conditions that led to this set-up in the first place...
Question for the blog...
Does anyone keep records on the TD's in order to study them further? Even after they drop status?
Its PGI31L that develops. Montgomery Research Group had a very large pouch synopsis (post 325) indicated that.
It is I think.
The first few frames show a low parked near the Cape Verde Islands, and then another one. Perhaps it is merging the two?
LOL
What model is that miami?, the one i saw had it going to NE
I believe the NHC will write up a full synopsis of the system sometime after the season is over.
Newport News /Hampton got it too when they released water out of the reservoir and flooded part of I64 and most of a low lying apartment complex.
12z GFS
It appears that they both probably are involved in development. It appears to be a complicated situation.
That 1012mb low ESE of Cape Hatteras is the remnants of the CV storm, which exited the coast of Virgina/Maryland near hour 336:
You ain't kidding. I think it's pretty irresponsible for folks to post the last frame of some 10 or 12 day model run. those same model runs have changed by several hundred miles since yesterday, and the storms don't even exist! Who knows what tomorrow holds, not to mention a week from now.
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