Three Atlantic threat areas may develop; a record fire season for the U.S.

A large tropical wave (Invest 94L) located about 1100 miles east of the Lesser Antilles Islands is headed west at 20 - 25 mph, and is showing increasing organization today. The storm is under light wind shear of 5 - 10 knots, and is over waters of 27°C. A large area of dry air lies just to the north of 94L, as seen on the latest Saharan Air Layer (SAL) analysis and water vapor satellite loops. This dry air is interfering with development, and this morning's visible satellite loop shows that 94L's heavy thunderstorm activity is sparse. However, the satellite loops do show that 94L has now separated from the clumps of heavy thunderstorms to its south, and a pretty well-defined surface circulation has developed. Heavy thunderstorms are now attempting to fire up around this circulation center, but are being hampered by dry air. The center of 94L was about 80 miles to the north of buoy 41041 at 10 am Monday morning, and the buoy recorded SW winds of 10 mph, confirming that 94L probably does have a closed surface circulation. The disturbance will have to build and maintain more heavy thunderstorms than it has now to be considered a tropical depression, though. The first hurricane hunter mission into 94L is scheduled for Tuesday afternoon.


Figure 1. Morning satellite image of Invest 94L.

Forecast for 94L
The latest 8 am EDT run of the SHIPS model predicts that wind shear will be low, 5 - 10 knots, for the next five days. Ocean temperatures will warm from 27°C this morning to 28.5°C by Wednesday morning, and the total heat content of the ocean will increase sharply during that period, as well. The main impediment to development will be dry air to the north, and the SHIPS model predicts the amount of dry air will change little over the next five days. I expect that 94L will continue to struggle with dry air through Wednesday, when it will probably have had enough time to moisten the surrounding atmosphere and protect itself against the dry air. The models have shown increasing unity in taking 94L through the Lesser Antilles on Wednesday, and I expect the storm will be a tropical depression or weak tropical storm with 40 - 50 mph winds at that time. In their 8 am EDT Tropical Weather Outlook, NHC gave 94L a 80% chance of developing into a tropical depression by Wednesday morning. None of the reliable models predict that 94L will reach hurricane strength over the next five days, and it is unlikely that 94L will be able to organize quickly enough to become anything stronger than a 60 mph tropical storm before reaching the Lesser Antilles, given the storm's current struggles with dry air, and the lack of model support for intensification. However, once 94L enters the Eastern Caribbean, wind shear will be low, oceanic heat content high, and the storm should have had enough time to moisten the atmosphere to allow steady strengthening to occur. The main factor that might prevent intensification into a hurricane late this week would be a close pass by the island of Hispaniola. Our top models for long-range 4 - 5 days forecasts all show a path for 94L very close to the island.

Will 94L hit the U.S. mainland?
This storm is a long-range threat to the U.S., as historically, 16% of storms in 94L's location have gone on to hit the U.S., with North Carolina the preferred target (10% chance.) A trough of low pressure capable of pulling 94L to the north enters Western Canada Thursday night, and the exact timing and amplitude of this trough will determine the ultimate landfall location of 94L. The long range 7 - 14 day runs of the GFS model over the past three day have all predicted an eventual landfall for 94L in the U.S., though these long-range runs are notoriously unreliable. The predicted landfall locations have ranged from New England to Texas--which isn't much help. The past three runs beginning on Sunday afternoon have all taken 94L over Florida during the August 27 - 29 time frame, which I'm sure is making organizers of the Republican National Convention uncomfortable, since the convention is in Tampa August 27 - 30. However, 94L could miss Florida completely, as the average error in model forecasts going out 7 days is in excess of 500 miles. We can't rule out a North Carolina landfall, but the pattern we've seen so far this year is for landfalls in Mexico's Yucatan Peninsula, so a more southwards path for 94L into the Yucatan is definitely a possibility. Also, we have that huge drought region in the Midwest, which tends to create its own high pressure bubble, which reduces the odds of storms making the turn and hitting the Central or Western Gulf Coast. If 94L makes it to the Western Caribbean, I see the two most likely options as a landfall in Mexico's Yucatan Peninsula (and then westwards into Mexico south of the Texas border), or recurvature into the Florida Gulf Coast.


Figure 2. MODIS satellite image of Hurricane Gordon taken on Sunday August 19, 2012, at 11:55 am EDT. At the time, Gordon was a Category 2 hurricane with 100 mph winds. Image credit: NASA.

Gordon hits the Azores
The eye of Hurricane Gordon passed over Santa Maria Island in the eastern Azores Islands near 1:30 am EDT this morning. Gordon was a Category 1 hurricane with 75 - 80 mph winds at landfall. Winds at the Santa Maria airport reached a sustained 49 mph at 3 am EDT, but the airport did not report winds during passage of the eyewall at 1:30 am. Reuters reported that Gordon caused only minor flooding and power outages. The hurricane is being sheared apart by strong upper-level winds, and the extratropical remnants of Gordon will not bring any strong winds or significant rain to Europe.

Disturbance 95L in the Gulf near the Texas/Mexico border
A region of disturbed weather (Invest 95L) has developed in the Gulf of Mexico off the coast, just northeast of Tampico, Mexico. The disturbance is due to a trough of low pressure and its associated cold front which moved off the coast over the weekend, but has been fortified via moisture from Tropical Storm Helene, which made landfall Saturday near Tampico. If 95L were to develop into a tropical storm, it would receive a new name. In their 8 am EDT Tropical Weather Outlook, NHC gave 95L a 30% chance of developing into a tropical cyclone by Wednesday morning. An Air Force hurricane hunter aircraft is scheduled to investigate 95L this afternoon. Winds at Tampico this morning were light out of the northeast, which implies that no surface circulation is forming at this time. Radar out of Altamira, Mexico does show some banding to the precipitation echoes, though, which may be indicative of something trying to spin up. The computer models show that 95L should move little over the next few days.


Figure 3. Radar out of Altamira, Mexico at 9:45 am EDT August 20, 2012, shows some banding to the precipitation echoes in association with 95L.

Disturbance 96L off the coast of Africa
The tropical Atlantic is very busy this third week of August, and this is the week of the year that we typically see a major ramp-up of tropical storm activity in the Atlantic. A new tropical wave that emerged from the coast of Africa Sunday (Invest 96L) is headed west at 15 - 20 mph. This disturbance has a modest amount of spin and heavy thunderstorm activity, and is under a moderate 10 - 20 knots of wind shear. In their 8 am EDT Tropical Weather Outlook, NHC gave 96L a 20% chance of developing into a tropical cyclone by Wednesday morning. This disturbance does not have much model support for development.


Figure 4. The new Suomi National Polar-orbiting Partnership satellite (S-NPP) carries an instrument so sensitive to low light levels that it can detect wildfires in the middle of the night. On August 17, 2012, the Visible Infrared Imaging Radiometer Suite (VIIRS) on Suomi-NPP acquired this image of the wildfires blazing in Idaho. The images were created with data from the instrument’s "day-night band," which sensed the fire in the visible portion of the spectrum. The Halstead Fire, centered about 18 miles northwest of Stanley, was sparked by lightning on July 27, and is burning in an area with large numbers of trees killed by the mountain pine beetle. As of Sunday afternoon, the fire had burned 92,000 acres was only 5% contained, according to InciWeb. The fire prompted the evacuation of the town of Featherville on Saturday night. Red flag warnings for adverse fire weather were posted in the region yesterday, and temperatures reached the low 90s with 16% humidity and winds of 10 mph. Image credit: NASA.

A record fire season in the U.S.
Massive fires continue to burn in Nevada, Idaho and California, and fires that are currently active in the Western U.S. have consumed over 1.3 million acres of land--an area approximately the size of Delaware. Thanks to widespread drought and unusually high temperatures over the past month, 3 million acres have gone up in flames since mid-July, and the fire season of 2012 now ranks in first place for the most acreage burned at this point in the year. According to the Interagency Fire Center, 6.8 million acres have burned as of August 19 this year, beating the previous record set just last year (6.5 million acres for the year-to-date period.) The Interagency Fire Center shows year-to-date records just for the past ten years. The 2012 fire season is well ahead of the pace of 2006, which was the worst fire year in the U.S. for total acreage burned in a year (records began in 1960). In 2006, 9.9 million acres burned, and 6.4 million acres had burned by August 19. With drought conditions far more widespread this year compared to 2006, and the latest forecasts calling for little drought relief over the coming two months, 2012 is likely to surpass 2006 as the worst fire year in U.S. history before the end of the year.


Figure 5. Comparison of drought conditions between the previous record fire year in the contiguous U.S. (2006) with 2012. Drought is much more widespread in 2012 compared to 2006, and 2012 will likely finish ahead of 2006 for the most acreage burned since record keeping began in 1960. Image credit: U.S. Drought Monitor.

Global warming expected to increase fire activity in the Western U.S.
As I blogged about in June, the severe fire seasons of 2012 and 2011 fit the pattern of what we expect to see more of with global warming. Hotter heat waves dry out vegetation more readily, resulting in increased probability of more acreage burned. A study published in the Journal Ecosphere in June 2012 used fire models driven by the output from sixteen climate models used in the 2007 IPCC report and found that while 8% of the planet should see decreases in fire activity over the next 30 years, 38% should see increases. By the end of the century, 20% of the globe should see decreased fire activity, and 62% increased fire activity. In the U.S., the regions most at risk of increased fires are the tundra regions of northern Alaska, and the West, with Arizona and Colorado at particularly high risk.

Jeff Masters