Wednesday, August 28, 2013

Where are the hurricanes?

We're reaching the traditional peak of hurricane season in the Atlantic and Caribbean basins, yet there isn't a sign of tropical weather activity.

Barring an explosion of development in September, it appears as if the long-range forecasts of an above-average number of named storms this year will fall flat.

After a bit of activity in late July and early August, the Atlantic, Caribbean and Gulf of Mexico have been largely quiet for the past several weeks.

Some of the ingredients for tropical storm development are there, but one factor -- strong high pressure in the Atlantic -- is not around. Instead, weaker high pressure has dominated the Atlantic this summer. The strongest high pressure has been over the western United States, with a low pressure trough hanging over the eastern part of the country, and a weak Bermuda high in the Atlantic.

Tropical storm development requires high pressure near the low pressure system.  Air from the high pressure is fed into the developing low, aiding the system to strengthen.  With weaker high pressure in the Atlantic, the few systems that developed have not strengthened.

In addition, hot dry air has been blown off the African coast by the jet stream since early August. That dry air inhibits the development of tropical storms and hurricanes.

I've seen some forecasts of conditions changing in the first 10 days of September, but it's quiet now.

Incidentally, this will mark only the sixth year since the late 1940s that we've made it to September 1 without a hurricane. The last time was in 2002. The other years were 1967, 1984, 1988 and 2001.

Thursday, August 22, 2013

Finally ... dry weather

It is coming a few days later than expected, but it appears as if an extended period of dry weather is coming to the Carolinas.

It will start this weekend with some beautiful conditions, but by later next week, our Charlotte-area weather will turn very summer-like.

I mentioned last week that some of the long-range computer models were hinting that our seemingly endless run of wet weather would be replaced by drier and rather warm conditions. That was supposed to have happened sometime around now.

Instead, it looks as if we'll have another shot of thunderstorms Friday, as a cold front moves through the region. But high pressure moving in behind the front will dry things out.

Saturday's weather figures to be pretty nice, with highs in the mid 80s. Sunday might be a degree or two cooler, and humidity levels will be quite low.

The forecast next week, when Carolinas children return to school?  It figures -- traditional summer weather will arrive.

For the first time that I can remember all summer, we'll see a big high pressure ridge establish itself across all of the South.  That will suppress precipitation chances and bring an extended string of clear days.

Meteorologists expect a week of dry and mostly clear weather.  Temperatures early in the week will be in the low and mid 80s for high temperatures, but we're expected to be near 90 by later in the week.

Meanwhile, the tropics continue to be quiet.  There's no sign of tropical storm development, and we're now moving into the height of the season.  If activity doesn't pick up soon, it might be time to revisit all those forecasts about a busy tropical weather season.

Friday, August 16, 2013

Wet weekend ... but how wet?

Hopefully, you've buried any plans for summer-type outdoor activities this weekend.  That ship has sailed.

Rain and chilly weather is certainly in our future the next few days, but there's a question about exactly how much rain is coming?

That's a sensitive topic in this part of the world, given our flooding episodes of June 28, June 30, July 11, and July 27.  And there's a chance that some heavy rain could fall again this weekend in the Carolinas, although the betting right now is on the eastern part of the two states.

The culprit will be a tropical system in the Gulf of Mexico.

The National Hurricane Center expects the low pressure system to move west-northwest, from its current position near Mexico's Yucatan Peninsula toward the Mexico-Texas border on the other side of the Gulf. But many forecasters also expect a lot of the system's moisture to be transported northeast, across the Florida Gulf Coast and into Georgia and the Carolinas.

This would happen Saturday, most likely, although it could continue into Sunday.

Justin Roberti of Accu-Weather says the highest chance of flash flooding this weekend in the Carolinas will be in the central and eastern parts, but the corridor drawn on an Accu-Weather map supplied to the media extends westward into Charlotte's eastern suburbs.  We're talking about Union, Anson, Stanly and Lancaster (S.C.) counties, and possibly into eastern Mecklenburg.  That's mighty close.

Bottom line ... be prepared to get quite wet this weekend.

Wednesday, August 14, 2013

Tropics getting active again

After a couple weeks of inactivity, the tropics are warming up again.

The satellite map Wednesday afternoon showed two potential named systems, one of which could be a player in the Charlotte-area forecast later this week.

That system was centered over the northwest Caribbean Sea on Wednesday afternoon.

The National Hurricane Center says there's a 60 percent chance of development into a tropical depression or storm within the next three days, and a 70 percent chance over the next five days. That system is expected to push northward in the Gulf of Mexico.

While a few computer models take the system westward, toward the Mexico-Texas border, most forecasts show the storm aiming at the Gulf coast, especially from Mississippi eastward to the Florida Panhandle.  If that happens, a dying tropical system could spread heavy rain into the Southeast.

Right now, it looks as if Georgia, western South Carolina, and Tennessee are most at risk of heavy rain Saturday and Sunday.  But it wouldn't take much of a course adjustment to bring the heavy rain into the Carolinas.

The other area being watched is in the eastern Atlantic -- a classic Cape Verde system.

On Wednesday afternoon, an area of disturbed weather was south of the Cape Verde Islands, and the Hurricane Center is calling for an 80 percent chance of development over the next five days.

It's far too early to tell what might happen to that system, although conditions in the central Atlantic are not exactly conducive to development.  But after being quiet for several weeks (due at least in part to dry air being blown from the Sahara Desert into the ocean), it looks like the eastern Atlantic is becoming an active area again.

And it's just in time for the tropical season to reach its peak.

Tuesday, August 13, 2013

The 'August Cool Snap' Theory

The cool snap predicted for later this week is no surprise to some people in the Carolinas.

Over the years, I've heard several different versions of the "August Cool Snap" theory, which states that Charlotte's brutal summer heat usually is broken -- for a few days, at least -- by cooler weather at some time during August.

I first heard about it from the late Gerry Leland, who worked at The Observer for 37 years before retiring in the 1990s. He believed the cooler temperatures came in the second week of the month.

Attorney Dick Huffman in Salisbury reminded me about the theory again Tuesday morning. He was married 30 years ago today, and he recounted how he quieted his bride-to-be's fears about a hot mid-August day by telling her the weather would be fine.

"To my amazement, it was wonderful, with highs in the upper 70s or low 80s," Huffman recalled.

He says that many years, he has noticed a spell of cooler weather sometime around his anniversary, although he says it doesn't always take place.

Meteorologists say a Canadian high pressure system will limit daytime highs to the upper 70s and lower 80s Wednesday and Thursday, and thick clouds and rain could do the same thing Friday and Saturday.

So I went back and looked at August weather over the past 10 years, and like many other statistical studies, it's a matter of interpretation, to some degree.

Do you call it a "cool spell" if daytime highs are 85 to 87 degrees, but morning lows are around 60 -- about 10 degrees below average.  Lows of 60 degrees signal very low humidity, and that would feel very nice in the middle of August.

Here is what happened the past 10 years, and I'll let you decide on this issue of the August Cool Snap.

2012 ... From Aug. 13-17, we had a stretch of days with highs in the mid 80s, but morning lows in the low 60s. Humidity levels were quite low.

2011 ... After hitting 90 or more on nine of the first 10 days of the month, it got more moderate. Morning lows on the 16th and 17th were near 60 degrees.

2010 ... Forget it!  There was nothing remotely close to a cool down.

2009 ... The high on Aug. 12 was only 74 degrees, and morning lows from Aug. 13-16 were in the mid 60s.

2008 ... The first 10 days were hot (mostly 90s), but it was a lot cooler on the 13th and 14th. Aug. 13 had a high of 76 after a morning low of 60. The next day, the high and low were 82 and 61. Temperatures stayed moderate for the next week, before turning hot again at the end of the month.

2007 ... Worse than 2010. There were six days of 100 degrees or more, and Charlotte hit at least 90 degrees every day in August.

2006 ... A definite cool down from Aug. 11-13, with a high of 73 on the 11th and morning lows in the low 60s.

2005 ... From Aug. 7-10, highs were only in the mid 80s, but it was warm at night.

2004 ... The poster child for the August Cool Snap theory.  The morning low on Aug. 7 was 50 degrees (a record), and it was 55 on Aug. 8. Daytime highs were only 80 degrees.

2003 ... The beginning of the month was moderate, with highs in the low to mid 80s. It got hot late in August that year.

Monday, August 12, 2013

Summer to arrive ... just in time for school?

I spent last week at the North Carolina coast and had planned to write about the big difference in weather this summer between the Piedmont and the beaches, but that will have to wait for another day.

There's a bigger story to talk about -- a potential shift in the weather pattern next week.

Both the Global and European weather models are predicting a big change, starting about the middle of next week (sometime around Aug. 21). If you believe what the models are saying, we'll see the start of some typical summer weather in the Carolinas.

Naturally!  It'll arrive near the end of meteorological summer, just in time for school to start.

Since the beginning of June, we've been locked -- most of the time -- in a pattern dominated by a trough in the eastern United States and Bermuda high pressure. The trough has allowed the jet stream to dip into the Southeast, and that has produced frequent rounds of stormy weather and plenty of days when high temperatures fell short of seasonal averages.

We've finally hit a string of 90-degree days, but that has been the exception. For the most part, it has been a cloudy, stormy summer.

The GFS and Euro models indicate that will change next week -- after the cold frontal passage late Tuesday, then the two or three days of unseasonable cold air damming, and then a possible tropical system over the weekend.

The Global model predicts high pressure will establish itself somewhere near the Mississippi River and dominate our weather for at least several days.  That would indicate hot and dry weather for the latter one-third of August.  The European model predicts the jet stream will be pushed back into Canada (where it typically exists in the summer), and the Southeast will be under the influence of a Bermuda high.  That would mean hot, sultry conditions, with a few afternoon and evening storms.

Either of those solutions would be a lot more typical of what we expect in the Carolinas during the summer.

Of course, those are 10-day forecasts, and the accuracy is a lot less stellar than short-range predictions.  It will be interesting to see how this develops.

Thursday, August 1, 2013

What happens in August?

There are several things I'm certain about in August.

School will start, and the many thousands of students headed to the classrooms will include my granddaughter Gracie, entering kindergarten.

The Panthers will win a couple exhibition games, and some of their fans will predict a 13-3 season and a Super Bowl appearance. The Tampa Bay Rays and Pittsburgh Pirates will keep winning. My Cleveland Indians won't.

And I'm pretty certain -- based on everything I've seen -- that August weather in the Charlotte region will look a lot like June and July.

Oh -- and your August vacations at the Carolinas beaches probably won't be impacted by tropical storms or hurricanes.

In short, August looks like another month of no heat waves and a lot of unsettled weather.  I fear we haven't seen the last of severe thunderstorms and flash flooding.

Our summer weather so far has been the result of a blocking pattern. For most of the past two months, we've had a Bermuda high pressure, another high pressure system in the western United States, and an area of weakness (a trough, or dip in the atmospheric currents) in the eastern United States.

That dip has brought a string of low pressure systems into the Southeast.  Sometimes they've been accompanied by cold fronts, most of which dissipate somewhere in the Carolinas.

That has produced some monumental rainfall totals, like the 25-plus inches since June 1 in Hickory. Some areas in the North Carolina mountains have exceeded their average annual rainfall totals, with five months still to go.

The long-range computer models point to a continuation of the pattern.

If this type of pattern develops in winter, those of us in the Carolinas are using snow shovels and ice scrapers.  In the summer, it means moderate temperatures and a lot of rain.

Tropical weather activity should be quiet in the Atlantic for the next few weeks. Satellite photos show a lot of dry air being blown westward into the Atlantic from Saharan Africa.  That usually puts a lid on the development of tropical storms and hurricanes, and forecasters seem to think it will continue into at least the middle of August.

That won't stop the development of tropical systems in the Gulf of Mexico, but the Carolinas coast should catch a break for at least a few weeks.

Remember, though. Once conditions become more favorable for development in the Atlantic, the current pattern over the eastern United States (Bermuda high and eastern U.S. trough) would favor tropical storms and hurricanes making a run at the Southeast coast.