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.

(more…)

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.