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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One and Two is favorable, although, like you said, we just don't know with the MJO forecasts. ;)
Date of report(UTC): 2010/08/17 18:34
Author of report: José Meitín
Submitted at: 2010/08/17 18:39
Pouch Name:PGI27L Initial Center Point: 15N 63W
OPERATIONS SUMMARY:
Today the GV completed a 5.5 hr mission into PGI27, bracketing
the pouch south-southwest of Puerto Rico.
23 dropsondes launched
http://catalog.eol.ucar.edu/cgi-bin/predict/report/index
Has a lot of showers and thunderstorms to work with, but is extemely disorganized at the moment.
Looks like some will get their wish here soon. Maybe they'll think differently after some suffer the consequences....which I hope doesn't happen.
Yep. No matter where you live, even if you live in Maine or Nova Scotia, you should always be prepared, and if you were prepared, you would have prepared safely for Bill of last year.
Read back the past page or two - we've been discussing model runs for that time period and what they MAY or MAY NOT indicate.
Anyhow, Ike what was your thoughts on the blog?
Hurricanetracker, did you catch this part?
"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 "
you guys have cars down there??? lol JK
Should be interesting to see what happens:
Climatology says Dr. Masters is correct.
Meaning lower pressures in the TNA. Things should get very interesting for the last two weeks of August...
Afternoon Baha,
I will find it interesting to see what we may learn with the data from the PREDICT and GRIP projects.
I'm going to say it is PGI31L who ends up interacting with PGI30L.
What is the elevation of the island, how far above that is your house, is it anchored deeply using concrete or the anchor shallow? How long do you think you can live on your roof before help can get to you?
OMG, it was a joke! Do you see the wink?
So the lower the NAO the higher a chance for development?
Yep, and at the "cheap" station gas is only $4.50 per gallon.
looks like NW
At least its cooler outside!! Thank ya mother nature for that!
The infamous 1938 Long Island Express hurricane hit Conn. Here is a quote about it from Wikipedia:
Connecticut
Connecticut was in the eastern side of the hurricane. Long Island acted as a buffer against large ocean surges, but the waters of Long Island Sound rose to unimaginable heights. Small shoreline towns to the east of New Haven had nearly complete destruction from the water and winds. To this day, the 1938 hurricane holds the record for the worst natural disaster in Connecticut's 350-year history.
The storm centre landed near New Haven, CT.
I don't think there is a part of the Atlantic coast of the US that is not potentially vulnerable to a hurricane.
Never hit Conn??? This just some
1944 September- 15 - Great Atlantic Hurricane - Category 3 in southern New England. Eye over Conn. /Rhode Island border. Severe wind damage in southeastern Massachusetts and across the Cape and Islands. On Cape Cod and Martha's Vineyard considered worse than 1938. Severe wind damage in New Bedford Mass. Much structural damage and much of the forest that had somehow escaped being decimated in 1938 fell victim to this storm.
1971 - Doria - August 28 - was in process of becoming Category one hurricane as it moved into Connecticut from Long Island. Hurricane force winds measured at sea level in Bridgeport Conn. Gusts to 80 mph (129 km/h) in southeast Massachusetts and Blue Hill.
1985 September 27–28-Hurricane Gloria- cat.1/2- first hurricane of significant strength to move inland in southern New England since 1960. Widespread wind damage reported in Conn, RI, and MA, later into coastal NH and Maine. Tree damage in Conn. worst since 1938 and wind losses in RI and eastern Massachusetts considerable to trees, utilities and roofs. New Bedford, MA reported wind gusts over 90 mph, inland Rehobet, MA state police barracks reported 120 mph and also later reported a tornado in vicinity. Winds at airport in Warwick, RI gusted to 85 mph at top of the hour reading. Winds on East Side of Providence near Brown University clocked at 100 mph. Winds in New London,Conn clocked at 110-112 mph. Widespread forest damage in Maine. Storm still had hurricane force wind gusts into New Brunswick, Canada.
Maybe this is when PGI31L will interact with PGI30L as noted in the PREDICT pouch synopsis for PGI31L.
"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."
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