The climate researchers at Colorado State University have released their spring forecast for the 2009 Atlantic hurricane season, and it’s calling for a relatively normal number of storms compared to average. The outlook is for 12 named storms, six hurricanes and two intense (category 3 or greater) hurricanes. The average from 1950-2000 is 9.6 named storms, 509 hurricanes and 2.3 intense hurricanes per year. There is a 54% chance of a major hurricane striking the US coast this year.

To develop their April forecast, the CSU researchers use a combination of observed sea surface temperatures in the Atlantic and sea level pressure off the African coastline in early spring. The observed values tend predict how much wind shear there will be from August through October, the heart of the hurricane season. The forecasters also look at analog years, where weather conditions are similar to this year. The number and intensity of storms in those years should be similar to what we get this year. Analog years for this season are 1951, 1968, 1976, 1985 and 2001.

The researchers also look at the chances of there being an El Nino or La Nina during the late summer. In El Nino years, the amount of tropical activity tends to diminish. Right now, we are in a weakening La Nina (cold sea surface temperatures in the central Pacific). There is a 50% possibility that La Nina conditions will develop by summer, and this caused the team to moderate its December forecast, which had called for 14 storms and seven hurricanes.

You can read the full forecast (PDF) here.

Earlier this week, the Dr. Gray and his team at Colorado State University issued their initial outlook for the 2009 hurricane season. The early outlook predicts a continuation of the above-normal tropical activity we’ve seen over the past few years. The outlook is for 14 storms, compared to over nine in a normal year, and seven hurricanes, compared to six in a normal year. There should be three major hurricanes, and there’s a 63% chance of a major hurricane making landfall somewhere in the United States–about 20% greater than in a normal year.

Last year at this time, CSU predicted there would be 13 named storms, seven hurricanes and three major hurricanes. The result ended up being 16 storms, eight hurricanes and five major hurricanes, so they underestimated. However, their new model for predicting hurricanes from this far out is apparently more accurate than the model they used previously.

A few other weather tidbits:

if tonight’s full moon seems brighter than usual, it’s because the moon is closer to the earth than it’s been for the past few years, and the first time in 15 years that the close approach, caused by the Moon’s elliptical orbit, has occurred during a full moon. Coincidentally, the moon is riding higher in the sky than any other full moon this year. The sun and moon follow opposite visual paths–when the sun is low close to the winter solstice, the moon is high in the sky, while in the summer, when the sun is overhead, the moon is low in the sky.

Another astronomical factoid — today is the first day that the sun begins to set later in the evening than it has since back on July 5th. Day will continue to shorten for another ten days, due to the sun rising later. We won’t get an earlier sunrise until January 13th.

The storm that brought welcome rain to much of the southeast is now history, having moved up the east coast and causing major power outages in the northeast. Much of Massachusetts was caught in an ice storm, with considerable damage. Albany, New York had .6 inches of ice, while Schenectady reported .88 inches of accumulated ice.

We are about to see a big pattern change in the weather across the United States. The past month or so has been dominated by an upper level trough in the east and a ridge in the west. This pattern brought warmer than normal conditions to the west, and colder than normal weather to the east, as the jet stream dived south, following the path of the trough.

Now, a trough is developing in the west, which will bring colder than normal weather there, but more seasonable, if not warmer than normal weather to the Southeast. There’s a better than normal chance of above normal temperatures for most of the south through Christmas, and it looks like we’ll get some additional rainfall, too. Lake Lanier’s current level is 1051.88 feet–more than ten inches above where it was on Wednesday before it started to rain. The AJC reports that yesterday was the first day since the record low level last December that the lake level in 2008 was higher than it was on the same day in 2007.

The August heat wave looks like it will go on through Thursday, but at least here at my house, today was the warmest day so far in 2008. It got up to 99 degrees (well, 98.7) at 2:10 PM, topping the 97.1 reached on both June 8 and July 10. It could have been worse though: with the dew point in the low 60s, the heat index was only 102 degrees.

Temperatures reached the century mark today in Augusta, Milledgeville, Savannah, Athens and Vidalia. For whatever reason, it stayed a bit cooler in Atlanta today, with highs only in the low 90s. Tomorrow, the humidity goes back up, and by tomorrow afternoon, the approaching front will bring a chance of rainfall, and at least a temporary end to the excessive heat we’ve been seeing recently.

Hurricane Forecast Update

We’re about ready to get into the strongest part of the hurricane season, from mid-August through the end of October.  The folks at Colorado State University have updated their tropical forecast and are now calling for more storms than they predicted back in April and repeated in June.

Instead of 15 named storms, the predicted total has been upped to 17, with nine hurricanes, instead of eight. Five of those should be intense, compared to four predicted previously.  Part of the reason for upping the predictions is the number of storms we’ve seen through July, with four named storms, two hurricanes and one intense hurricane. That doesn’t count Edouard, which was the first storm in August.  According to the forecast, only 2005 (the year of Katrina) and 1916 have had more active pre-August tropical activity.

There’s a 2/3 chance of a major hurricane making landfall somewhere in the US during the rest of the season, with a better than 40% chance of a storm striking either the east coast or the gulf coast.  Overall, the forecasters are predicting a tropical season that is 190% as active than the average season from 1950-2000.

In addition to providing forecasts for the rest of the season, the Dr. Gray and his team are providing a forecast for August tropical activity. If they are right, we will have four storms, three of which will become hurricanes, and one intense hurricane this month. With Edouard already occuring, that’s the non-hurricane storm, if their forecast is correct. They will also issue forecasts for September and October at the beginning of those months.

The temperature here in Lawrenceville topped 90 degrees for the first time in 2008 today, with a maximum of 91.4 degrees at 2PM.  In Atlanta, today’s high was only 89.  But in any case, they’ll have another chance tomorrow and indeed for the next week or so, as we are under the influence of an upper level high pressure system that will keep the warmer than normal temperatures around, and probably keep the rain away as well.

All in all, temperatures are running about 6 degrees above normal for early June.  And, this is about the usual time we see 90 degrees — last year we topped 90 on June 6th, in 2006 on May 24th, and in 2005 on June 14th.

Longtime blog reader Morgan Kemp reminds us of the ongoing drought by posting some comments by Georgia climatologist David Stooksbury made at this time last year, when the drought’s effects were really setting in. Actually, we’re doing a bit better this year through May.  While most of Georgia had less than normal rainfall for the month, Atlanta is only 4 inches short of normal for the year, and Athens has had 6.4 inches less than what would be expected.  Through the end of May, Atlanta recorded 18.65 inches of precipitation for 2008, compared to 11.73 inches for the same period in 2007.

It does seem like things are getting dry, however.  While some parts of North Georgia saw beneficial thunderstorms over the last week or so, they all missed me.  And, Climatologist Stooksbury issued a new report today warning that the hot, dry weather is likely to erase the effects of the improvements we’ve seen this year.

Much of the report is simply a recap of where different parts of the state stand with water supplies and rainfall.  However, for the second year in a row, he predicts warmer than normal temperatures if we don’t get rainfall, and says,

For the next several months, Georgia’s best chance for widespread drought relief will be tropical disturbances. However, the tropics usually don’t become active until late summer.

June and July are critical. Without major rain events the soils will continue to become drier leading to lower stream flows, groundwater levels and reservoir and pond levels.

The outlook for an above normal tropical season remains strong, according to the latest update from Dr. Gray at Colorado State University, which maintained the same outlook as he did in April. And, there’s a better chance of tropical weather affecting the US mainland than there was last year.

Meanwhile, look for a better chance than normal for hot temperatures for the next two weeks, with rainfall remaining about normal. For the month as a whole, we’ve got equal chances of above or below normal rainfall and temperatures, according to the updated outlook from the Climate Prediction Center.

With less than two months until the start of the Atlantic tropical season on June 1, the forecasting team at Colorado State University has updated its forecast, and is now calling for a more active season than originally predicted last December.

Drs. Klotzbach and Gray are estimating that there will be 15 named storms and eight hurricanes in 2008, with four of those being intense hurricanes.  This compares to the December forecast of 13 named storms, seven hurricanes, and three intense hurricanes. Between 1950 and 2000, there were, on average, 9.6 named storms, 5.9 hurricanes, and 2.3 intense hurricanes each year.  Overall tropical activity is predicted to be 160% of normal.

There is a 99% chance that some sort of tropical activity will cross the US coastline this year, with a 69% chance of a major hurricane making landfall.  There is a 44% chance that a major hurricane will strike the Gulf Coast, and a 45% chance that a major hurricane will strike the East coast or the Florida peninsula.

The forecasters are using a new methodology for predicting this year’s season; the second year in a row that they have changed their system.  Part of the forecast relies on sea surface temperatures in the Atlantic in February and March, another part examines the sea level barometric pressure in the Atlantic, and the last part is based on the December forecast.  The CSU team looked at these variables for past years, and did ‘hindcasts’ to see how well they predicted the following seasons, and have determined that they are more accurate than what was examined previously.

Another factor in the April forecast is to look at analog years — other years that have had a similar weather pattern in the spring compared to 2008 — and the tropical season that followed.  For 2008, they have chosen 1950, 1989, 1999 and 2000 as being similar weather-wise to what we have seen this winter and early spring.

You can read the entire forecast here (PDF).  They plan on an update on June 2nd, as the tropical season officially gets underway.

The team over at Colorado State University has released its initial forecast for the 2008 hurricane season, and the prediction is for another above-average season, compared to normal.  For 2008, the forecast is for 13 named storms, seven hurricanes, and three category 3, 4, or 5 hurricanes.

This compares to last year’s early forecast of 14 storms, seven hurricanes, and three intense hurricanes made in December, 2006.  The actual number of 2007 storms was 14, with six hurricanes, and two major hurricanes. Based on normal climatology, we would have 9.6 storms, 5.9 hurricanes, with 2.3 of those being major. Overall, the forecast for tropical activity in 2008 is 125% of normal conditions, based on the 1950-2000 period.

As far as the chance of a hurricane making landfall in the United States, there is a 90% chance of a strike somewhere in the US, with a 68% chance of landfall on the Gulf Coast, and a 70% chance of landfall in Florida and the East Coast.

In the forecast itself (PDF), Drs. Gray and Klotzbach explain that they are using a new methodology for their long range predictions. Essentially what they are doing is looking at a range of climate features, including sea surface temperatures, upper atmosphere pressure differences in the North Atlantic, and sea level pressures in the eastern Pacific, and using them as predictors of what might happen.  By observing these values in the fall of previous years, and then comparing the following hurricane seasons, they have determined that these three influences reasonably predict the upcoming season.

The forecast will be updated in April, and again at the start of the hurricane season in June.

While the 2007 hurricane season doesn’t officially end until Friday, for all intents and purposes it’s over, with no activity since the beginning of November, and nothing on the horizon.  Despite predictions for an active season, 2007 ended up being about normal.  Dr. Gray and the gang over at the Department of Atmospheric Science at Colorado State University have released their 2007 summary (PDF) with the numbers for the season:

We had 14 named storms, with six hurricanes and two intense hurricanes this year. Dean and Felix ended up as category 5 storms, and both ended up on the Yucatan peninsula in Mexico.  The remaining hurricanes were category 1, or relatively minor.  For the second consecutive year, the United States went relatively unscathed, with only Hurricane Humberto striking Texas creating any significant damage.  Tropical Storm Barry brought some drought relief to parts of Georgia, and helped put out the south Georgia wildfires.  However, a storm that might have put a significant dent in the drought did not appear.

The Colorado State team seems to be at a loss to explain the weaker than expected season.  Some of the factors that would point to a stronger season, including the development of La Nina conditions and a relative lack of vertical wind shear worked out as expected.  Atlantic sea surface temperatures were slightly cooler than predicted, but this should not have been a major factor.

While the first half of the season turned out to be relatively normal, less than normal activity in October and November counted for most of the shortfall from the earlier projections.   And, the report said that despite normal to lower-than-normal hurricane seasons in 2006 and 2007, we are still in a period of greater than normal hurricane activity that will last another ten to 20 years.  This long cycle is part of the Atlantic Multidecadal Oscillation that is also responsible for the southeast’s rainfall shortage.

As far as what 2008 will bring…well, Dr. Gray’s team plans to issue its first 2008 hurricane forecast on December 7th.

Early September marks the halfway point of the 2007 tropical season, and things are certainly busy, with more on the way. So far this year, we’ve had six named storms in the Atlantic basin, which is well above average. Especially notable is that there have been two category five systems, Dean and Felix, both striking the Mexican/South American coast.

The picture below was taken about 8 AM, and shows Felix striking the South American coast near the Nicaragua Honduras border:

Also today, Hurricane Henriette is making landfall on the other side of Mexico, and is forecast to head towards New Mexico and Arizona, bringing heavy rainfall to that area.

Of more concern to those of us on the Eastern seaboard is a tropical disturbance located off of the Georgia coast. This low pressure system has been milling around since last week, and has the potential to develop into a tropical storm that could bring rain to the Mid-Atlantic and New England states. The picture below shows what several models were predicting what the storm’s path could be:

Both this system and Hurricane Felix are affecting the weather in Georgia, as we are now centered between the two storms’ low pressure. This is bringing us the nice weather we have seen over the past few days. Depending on what happens with these storms, we are likely to continue to see dry weather, even if the system off the coast becomes better organized.

So what to expect as the tropical season goes on? Dr. Gray and his team have issued an updated hurricane forecast (PDF) for the rest of the season and there doesn’t seem to be any significant changes from what was earlier predicted. The team continues to predict 15 named storms, including Felix, but has dropped the number of hurricanes predicted from eight to seven. They are still predicting four intense hurricanes — we are now halfway there with Dean and Felix.

The forecast notes that through August 31st, observed tropical activity accounts for 40% of what would be seen during an average hurricane season. In a normal year, only 33% of tropical activity would be recorded during August.

Despite a relatively cool July —the mean July temperature was actually cooler than the mean June Temperature, both here in Lawrenceville and in Atlanta— it looks like August is going to be our hottest month of the year.

The short range, medium range, and long range forecasts are all calling for warmer than normal temperatures, and it looks like we may not get much rain to help out, at least until the middle of the month.

Temperatures will be approaching the 100 degree mark all this week in North Georgia. To make things worse, we’ll likely be seeing high dew points as well. That means that the humidity will be approaching the unbearable range. Take a look at the forecast dew points in Georgia for 2 PM Thursday:

If this forecast validates, we’ll see the heat index above 105 degrees, the danger level, several times this week.

Ultimately, it’s the moisture in the air that determines how we feel when we go outside. Although relative humidity is the measurement most people use to measure moisture content, the dew point temperature can provide a better measure of how uncomfortable conditions are. When the dew point rises to near 70 or above, most people are unlikely to want to be outside for very long.

The heat index also measures the apparent temperature. For more detail, take a look at this table showing the relationship between relative humidity, temperature, heat index, and dew point.

The reversal from the cool and wet July conditions to the hot and dry conditions for August isn’t going to do much to help the drought conditions in Georgia. Over the last month, the drought levels in Georgia haven’t changed very much. While the rain has kept lawns green in the short term, we will see a quick return to brown lawns without more rainfall.

As I’ve said before, tropical weather will probably be the key to breaking the drought. Despite the relatively quiet season so far, the latest forecast by Dr. Gray at Colorado State University is still calling for an above average hurricane season. The researchers are predicting 15 tropical storms for the season, down 2 from their May forecast, and eight hurricanes, down from nine in May. There’s also an above average chance of a major hurricane striking the US coast.

We’re almost two months into the official hurricane season, which runs from June 1st to November 30th, and so far, we’ve had only two named storms. Given the various predictions for between 13 and 17 named storms, it may seem to some that we’re not going to make it.

Keep in mind that the strongest part of the hurricane season is from mid-August to mid-October, when the Atlantic Ocean is at its warmest. With the exception of 2005 and 2003, when we had seven storms by the end of July, for the past ten years, we’ve seen two tropical storms each year before August 1st, except for 1998 and 2004, when there weren’t any storms at all in the first two months of the season, so we’re on schedule.

The approach of the strongest part of the hurricane season brings a reminder from the Georgia State Climatologist David Stooksbury that Georgia could be severely impacted should a Katrina-like storm hit the coast. In an article posted yesterday on the Georgia FACES website, Stooksbury reports that UGA students created a model of the storm surge from Hurricane Katrina, and then projected it along the Georgia coast, where it would cause a 20-30 foot storm surge.

“A storm surge of this magnitude would wash over the barrier islands and lead to massive flooding along the coast. Almost all of Georgia east of I-95 will be under water with a category 3 hurricane. Areas west of I-95 will see major flooding, too.”

The article also explodes some Georgia hurricane myths, and offers advice on preparedness.

Next week brings updates to the hurricane forecasts by the National Weather Service and Dr. Gray’s team over at Colorado State University, and it will be interesting to see what changes, if any, we see in the predictions.

Dr. Gray has written an op-ed article for this morning’s Wall Street Journal examining if the increases we’ve seen in the intensity of hurricanes recently is being caused by global warming. He compares two long term periods from the early 20th century and late 20th/early 21st, and concludes that the number of landfalling hurricanes in the US declined, despite the increase in carbon dioxide in the air.

Instead of following the politically correct line on global warming, Dr. Gray analyzes the patterns of ocean currents and salinity in the Atlantic over time, and concludes,

“The warming theorists — most of whom, no doubt, earnestly believe that human activity has triggered nature’s wrath — have the ears of the news media. But there is another plausible explanation, supported by decades of physical observation. The spate of recent destructive hurricanes may have little or nothing to do with greenhouse gases and climate change, and everything to do with the Atlantic Ocean’s currents.”

If you’re not a Wall Street Journal Online subscriber, you can read the article via Google News. Click this link, and choose the article “Hurricanes and Hot Air”.