We’ve almost made it through July. Seasonal outlooks from various sources such as NOAA, Colorado State, WSI, etc., have been mentioning the likelihood of an active season with above normal numbers of tropical storms, hurricanes, and major hurricanes. So far, we’ve only had one hurricane and one tropical storm. If you read across weather forums, blogs, Facebook, etc., many folks are already screaming “BUST” when the season really hasn’t even begun. One look at tropical cyclone climatology tells us that while the 2010 Atlantic Hurricane Season has gotten off to a seemingly slow start, we’re actually above average already.

It turns out that the Atlantic basin only averages about 10 named storms per 100 years by June 20th about about 20 named storms per 100 years by August 1st. This means that, on average, we only see about 1 to 2 named storms every ten years during the months of June and July. There are many above average years that we don’t see our first named storm until sometime in August. With Bonnie out of the way already, we are actually ahead of the climatological averages, whether the season has seemed slow so far or not.

Still, what has brought upon this seemingly slow start to the Atlantic hurricane season? Besides general climatology itself, there have been two main factors at play this summer. The first inhibitng factor so far this season has been the presence of wind shear across the Atlantic basin. Wind shear is often present across the Atlantic basin during the early part of the season as the temperature contrasts associated with the polar jet stream gradually shift further north into the mid latitudes. Quite often, this change doesn’t happen quickly enough during the early part of the season to not have an effect on tropical waves that try to develop. A second source of wind shear is in association with the strong central Atlantic high pressure and its subsequent increase in the low-level trade winds. These fast low-level winds make it hard for low-level cyclones to close off, and hence, make tropical cyclone formation hard to achieve. The third source of wind shear so far this season has been the presence of TUTT lows across the western Atlantic into the Gulf of Mexico. These have been developing as the high pressure ridge over the Southern U.S. and the high pressure ridge across the Central Atlantic “pinch off” upper lows across the western Atlantic, and these meander around, and often drift westward back into the Gulf, which is a climatologically favored area for tropical development during the early part of the hurricane season.

The other inhibiting factor so far this hurricane season is also related to the strong high pressure in the Atlantic Ocean. This high pressure and its strong low-level trade winds advect dry, dusty air from the Saharan Desert westward into the Atlantic basin. This SAL air mass is detrimental to tropical development because the dry air cuts down on the latent heat release from moisture in the atmosphere, which is a tropical cyclone’s fuel source, and the dry air is also associated with subsidence that helps preclude organized thunderstorm development. The image below illustrates the issue we’ve had with the SAL so far this hurricane season.

This is a common issue during summers with a developing significant La Nina. Climatologically speaking, the SAL is usually a decreasing concern as we head into the heart of the hurricane season, but during La Nina summers, it can be a problem a little later than usual.

Now that we’ve discussed what we’ve seen thus far (or in some cases, haven’t seen), let’s talk about what we can expect for the next few weeks? Honestly, not a whole lot… While the shear is decreasing with time across the Atlantic basin, it will still be an issue for the next at least 7-10 days as we continue to see these TUTT lows get pinched off near the Bahamas. The SAL air mass will also be another concern. The other thing we’re monitoring is the upward motion fields across the globe. The image below shows their expected progression as we head into early to mid August.

These are velocity potential anomalies at 200-mb. Areas in cool colors have upward motion potential while the warm colors have downward motion potential. It is easy to see that as we head into the next 7-10 days, we see a wave of downward motion and generally sinking air move into much of the Atlantic basin. Such a pattern often precludes significant tropical development because of the sinking motion being an inhibiting factor in the development of organized and sustained thunderstorm clusters. By the end of the forecast cycle, a “wave” of upward motion potential starts to move into the Atlantic basin, and by this time, we may see an upswing in potential activity.

The next few images are from the ECMWF and GFS ensembles to depict the expect large scale pattern for the next couple of weeks.

Medium range guidance is in decent agreement through the next 10 days in the idea that the ridge of high pressure across the Southern United States will remain firmly in place while troughing starts to develop along the East Coast. By 300 hours out, it appears that while the ridge retreats westward a little bit (not by much), troughing along the East Coast further establishes itself. What effects will this possible have?

Within the next week or so, it is possible that a “homegrown” system may try to develop in the Bay of Campeche along the western end of a washed out frontal boundary. IF such a system were to develop, the ridge across the South would push it westward toward the Mexican coast… southern Texas as a northern extreme. As we head on into August, we will be turning our attention to systems coming off the African Coast and tracking south of the Cape Verde Islands. The highest potential for development from these waves will be out across the Central Atlantic, with two favored tracks. The first favored track will be the westward moving “Caribbean Cruiser” track for lower latitude systems. These move westward in response to high pressure to the north and are a “popular” track during significant La Nina summers for that reason. The other favored track will be for systems coming off the African coast at a higher latitude to recurve in the western Atlantic in response to the troughing off the East Coast. This is also another classic La Nina track, and is also a pattern favorable for tropical cyclone threats to the island of Bermuda. However, if we see one of these systems take its time in developing, it is possible that it misses the troughing to its north across the East Coast, and instead, moves westward toward southern Florida and the Gulf of Mexico in response to the ridge across the USA. These systems generally track westward once they get into the Gulf of Mexico.

So, with this said, where are the relatively higher landfall risk areas for the next couple of weeks? Let’s take a look…

The biggest concern area for the next couple of weeks along the U.S. coastline is going to be the Texas coast, stretching into western Louisiana. This area will have to watch systems coming out of the Carribean, the Bay of Campeche, and even from the Bahamas if any systems are able to miss the troughing to their north along the East Coast and shoot westward under the ridge. These particular systems also deem it necessary to place the central Gulf Coast in a “moderate” landfall risk because sometimes there can be enough of a weakness in the ridge, especially in association with TUTT lows, for a slightly more northwestern track to ensue in the Gulf. However, when compared to the more westerly tracks, this isn’t quite as likely to happen. The next area of greatest concern will be in southern Florida with systems that track across the Bahamas and then shoot westward under the ridge. Areas such as Key West, Miami, and Ft. Lauderdale will really have to watch for this potential. Once these systems move into the Gulf, they will generally be in a favorable environment for significant develop, but will mainly be on a westerly coast. While not as high of a risk as the above mentioned areas, the third area of relatively greater risk will be the Outer Banks of North Carolina with any potential system that gets too close to the coastline to make a complete miss as it recurves back out to see. In contrast, the areas of lowest landfall risk are along the Mid Atlantic coastline as they will be protected by troughing, and along the Big Bend area of Florida as systems in the Gulf of Mexico will be on more of a westerly course.

With all of this said, there are some important things to remember…

As we talked about earlier, while it seems we’ve gotten off to a slow start to this hurricane season, that just isn’t the case. When looking back at the past more than 100 years of weather records, our two storms so far this season actually puts us above normal in climatological averages. We go many years without seeing one named tropical storm until August. Even though it has seemed like we’ve gotten off to a slow start, an active hurricane season is STILL expected. We are JUST NOW getting toward the heart of the hurricane season, and the factors that have held us back from significant development so far this summer naturally fade away as we head into August and beyond. EXPECT an uptick in activity. Finally, even if the forecasts for an active season don’t pan out, remember that it only takes one storm. In 1992, there was only one hurricane the entire season, and it didn’t develop until late August. It also happened to be the first named storm of the season. It was Andrew, and it was a Category 5 hurricane that devastated southern Florida and then went on to strike Louisiana as a weaker but still major Category 3 hurricane. Regardless of the seasonal forecasts, YOU MUST BE PREPARED! The Alabama Storm Trackers will be monitoring the tropics as we head into the heart of this hurricane season, and we’ll be passing along the latest information to you as it becomes available……

Invest 97L is looking good on satellite imagery today. Convection is firing to the East and Southeast of the cyclonic circulation. The latest models have this heading to South Florida with a northward turn after it enters the Gulf of Mexico and a final landfall in the Florida Panhandle. It is still VERY early in the game and these tracks CAN and WILL change, but this is something that needs to be paid attention to. High pressure to the north could keep the system on a more westward track.

NHC has a 30% chance of development on 97L

Spaghetti Chart of 97L Guidance

The Alabama Storm Trackers will likely provide footage LIVE from the field should this become a threat to the Gulf Coast.
~Brandon

The Storm Prediction Center has upgraded most of Central and North Alabama to a slight risk of severe thunderstorms today, mainly along and north of a line from Phenix City to Montgomery to Centerville to Pickensville.

The main threat from these storms will be damaging wind gusts. Heavy downpours and frequent lightning cannot be ruled out either. If you must be outside today, stay close to a weather source, and act accordingly should you be caught in any of these storms.

Looks like some milder temperatures have arrived just in time for outdoor festivities regarding 4th of July celebrations area-wide. Expect temperatures in the upper 80s to low 90s across the area with lower humidity values. Areas to the south have some slight rain chances, but those showers will be hit-or-miss and shouldn’t put too much of a damper on any picnics, swimming, or boating. Remember, though, any storms that do form will have the capability of producing lightning. If you’re close enough to hear thunder, you’re close enough to be struck by lightning. Every one have a safe and enjoyable holiday weekend.

On to the tropics….

A weak area of low pressure in the northern Gulf of Mexico is drifting westward along a stalled frontal boundary. The National Hurricane Center has placed a 20% chance of development on this feature. Upper level winds are currently inhibiting development, but these winds could relax somewhat over the next 24 hours. We don’t expect any significant problems from this feature at this time other than some breezy conditions and slightly enhanced riptides along the coast.

Happy 4th, everyone!

~Brandon

The clearing line is progressing southward slowly this morning…..a sign of lesser rain chances in our future.  The best chance of a shower today will lie south of I-20 with better chances of anything scattered south of I-85.  Most of that will be thanks to a stalled out boundary that is drifting southward and some indirect effects of ex-hurricane Alex that slammed into Mexico last evening.

This is an image of Alex shortly before landfall off of the Brownsville NEXRAD site.  The pressure bottomed out at 947mb with maximum ESTIMATED sustained winds of 105 mph.  I tend to believe that this actually may have been a major hurricane (category 3) at landfall with a pressure that low.  The post storm NHC investigation will hopefully prove that.  This is the second strongest June hurricane EVER in the Atlantic basin. 

Alex looks to be strengthening this morning as visible satellite imagery shows deepening thunderstorm tops around the center of circulation.  A pressure drop to 959mb was indicated by Air Force Reconnaissance aircraft just before the 7am advisory this morning.  Alex currently has maximum sustained winds of 80mph and is moving NW @ 7mph as of the latest 10am CDT advisory.  This storm still has several hours over water and will affect portions of southern Texas even if the center makes landfall south of the border.  A Hurricane Warning is in effect from Baffin Bay, TX south to the mouth of the Rio Grande.  We expect Alex to strengthen to a category two hurricane later today.  Alex still has the potential to become a major hurricane before it makes landfall sometime late tonight or early tomorrow.

Given the image above, I wouldn’t be shocked to see Alex form over the next day or so.  The system is beginning to get a nice CDO (central dense overcast) overtop a mid level and potential low level circulation.  The thunderstorm flare-up is more condensed than the last couple of days and conditions are becoming more favorable for organized tropical development.  The system has been labeled Invest-93L.

The latest forecast model tracks are scary….given the oil spill crisis in the Gulf of Mexico along with the boiling hot water and weak shear forecast ahead of this developing system.  We don’t see this becoming a "major" US hit, but that can certainly change in a hurry given the potential conditions.  Track models are varying big time so I won’t go into specifics at this point on a potential forecast path, but we will get more into those possibilities later this weekend.

Another day full of twisters.  The Storm Prediction Center has a moderate risk of severe storms out for portions of the Central Plains today.  Tornado watches are already in effect with initiation taking place across WY, CO, NE, KS.  The particular storm above is the first to go tornado warned in Kansas today and already had a reported tornado by law enforcement in western Scott County, KS. 

Storm chasers are also in the field today and can be viewed on SevereStudios.com and ChaserTV.com.  We will bring you the images from the field as they are captured from some of the worlds best storm intercept teams.  If anything over the top happens, we will attempt to bring it to you first. 

On a side note….the 6/17/10 outbreak has produced at least 4 violent tornadoes across the states of North Dakota and Minnesota along with several other tornadoes.  The Grand Forks and Minneapolis NWS offices continue to investigate some areas and we will likely hear of more updates in the coming days.  Hated to see so many people lose thre homes and lives during that round of violent weather.  It’s that time of year for our neighbors to the north, however.  More later…

-Brett

A developing bow echo is moving across the area and is requiring the NWS in Birmingham to issue severe thunderstorm warnings for the entire area ahead of the line.  With our bow tracking overlay, you can see that this system will effect much of East-Central Alabama over the next hour as it begins to accelerate.  A Severe Thunderstorm Watch is in effect until 8PM CDT this evening for the entire area.  There could be some additional development following this line.  Well keep you posted.

A weather watch is now looking possible for portions of Central Alabama this afternoon as the environment is becoming very unstable with afternoon heating and sunshine.  The SPC will upgrade portions of the area to a convective slight risk on the 1630z update….or around 11:30am.  We will monitor the situation and keep you updated on the sitaution….the SPC text and statement of the MCD follows…

 AREAS AFFECTED...NRN MS...NRN AL...NWRN GA...ERN TN AND WRN NC

   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

   VALID 191530Z - 191630Z

   THREAT FOR MAINLY ISOLATED DAMAGING WIND WILL EXIST THIS AFTERNOON
   WITH STORMS DEVELOPING FROM NRN MS THROUGH NRN AND CNTRL AL...NWRN
   GA...ERN TN AND WRN NC. THIS AREA IS BEING UPGRADED TO A SLIGHT
   RISK...AND A WW IS POSSIBLE DEPENDING ON CONVECTIVE TRENDS.

   AT MID-DAY AN EXPANSIVE OUTFLOW BOUNDARY IS MOVING SOUTHEASTWARD
   THROUGH ERN KY AND ERN TN THEN WWD INTO NRN AL AND NRN MS. THE
   ATMOSPHERE SOUTH OF THIS FEATURE IS ALREADY MODERATELY UNSTABLE WITH
   2000-2500 J/KG MLCAPE. STRONG DIABATIC HEATING OF THE BOUNDARY LAYER
   WILL RESULT IN FURTHER DESTABILIZATION THIS AFTERNOON. FLOW ALOFT IS
   WEAK WNWLY ALONG NRN PERIPHERY OF UPPER RIDGE. HOWEVER...GIVEN THE
   PROPENSITY FOR STORMS TO ORGANIZE INTO MULTICELL LINES ALONG THE
   OUTFLOW BOUNDARY...A SLIGHTLY GREATER CONCENTRATION OF STRONG TO
   DAMAGING WIND GUSTS WILL BE POSSIBLE THAN IS USUALLY EXPECTED IN A
   PULSE STORM ENVIRONMENT.