Tuesday, June 30, 2009
A strong tropical wave flared up over the weekend, but interaction with the Yucatan Peninsula quickly ended its chance for development. Otherwise, the Atlantic basin is extremely quiet as a MJO pulse is exiting to the east and resulting in sinking air across the tropical waters. A TUTT is parked over Hispaniola and is contributing to strong upper level westerly winds across much of the basin. Any tropical waves moving in this environment will be significantly sheared by the strong winds. Another interesting development is occurring in the Caribbean Sea where stronger than normal low level winds are being observed. The Colombian heat low is primarily responsible for this anomalously strong low level easterly flow, and this will also rip apart any waves moving through the Caribbean. The only location where any development could occur would be off the Southeast U.S. coast or the Gulf of Mexico where a washed out frontal boundary remains. Showers and thunderstorms are occurring in the waters adjacent to Florida, but development in these areas also appears unlikely.
The Eastern Pacific is much more active than the Atlantic as a mass of thunderstorms exists off the Central American coast between 87 and 100 degrees West longitude. Closer inspection of the convection shows a cyclonic swirl south of El Salvador, and it's very possible this could be some remnant energy of Invest 93. In any case, the environment appears favorable for some development of this system in the next couple of days with wind shear remaining light, SSTs in the lower 80s, and a moist ambient environment. A larger mass of thunderstorms is centered near 10 deg N and 96 deg W, but this area does not appear to have any type of circulation at this time. However, wind shear remains on the strong side so short-term development of this system does not appear likely.
Very strong sinking motion is occurring in this basin since it is located east of a MJO pulse in the Indian Ocean. Therefore, short-term development looks very unlikely despite favorable shear and water temperatures in the main development region.
The most convection in any ocean basin currently resides in the Indian Ocean as a MJO pulse is moving through. This is much welcomed relief to India as they have experienced very hot, dry conditions for the last several weeks. Despite the active look on satellite, extremely strong wind shear covers most of the basin, and any tropical development appears unlikely in the short-term. However, this may be a blessing in disguise as India will receive rain without the damaging wind and flooding effects of a tropical cyclone.
The weather may be a little more tricky to forecast tonight as our upper air pattern is dominated by northwesterly flow associated with a big upper low over the Great Lakes. A subtle shortwave will eject out of this upper low tonight and will likely move just to our north. It's possible that a few showers could develop early tomorrow morning across Tennessee and Arkansas in advance of this energy. If a complex does develop, the upper air flow would move it very close to our area. On the other hand, it would be encountering a slightly less stable environment in East Central Mississippi so it's very likely that it would be weakening or even dissipate before it impacts the area. However, a few clouds will be generated by the upper level wave, and this may only allow temperatures to drop to 67 tomorrow morning. Looking ahead, the 4th of July weekend looks cooler, but the price to pay will likely be better rain chances. I still don't think many folks will gripe about that.
Monday, June 29, 2009
Friday, June 26, 2009
Thursday, June 25, 2009
Wednesday, June 24, 2009
Tuesday, June 23, 2009
The first is the potential impact of the Pacific Decadal Oscillation. Clearly, the PDO has been in a cold phase for the last couple of years, coinciding with the persistent La Nina conditions. However, since the first of May, SST anomalies have become positive across much of the North and Northeast Pacific Ocean; a cold pocket remains off the Alaskan Peninsula. It's interesting to note that the upswing in the SST anomalies across the North Pacific has coincided with the developing El Nino in the equatorial Eastern Pacific. If this pattern of positive SST anomalies continues or strengthens, the PDO may likely transition back to the warm phase. How soon this occurs remains to be seen, but a warm PDO would make it very difficult to have above normal temperatures across the Deep South and the eastern third of the United States.
Although the developing El Nino was the basis for their forecast, El Nino conditions typically cause cooler and wetter than normal conditions across the South. The key to this will be the placement of the subtropical jet stream. It tends to fluctuate between the Deep South and Florida during El Nino years, and a more suppressed STJ would keep above normal precipitation to our south. Regardless of the STJ placement, a warm PDO would make it difficult to have above normal temperatures for a four month period.
The second factor that was not considered, not surprisingly, is the Global Wind Oscillation (GWO). Given that we are headed for a weak to moderate El Nino, westerly winds will increase atmospheric angular momentum and should lead to the GWO persisting between phases 5-7 for much of the winter. If this indeed occurs, GWO composites for these phases correspond to cooler than normal temperatures across the South and Eastern U.S. As a caveat, more than wind direction (frictional torque) is factored into the GWO, but El Nino conditions generally cause the global circulation to vary from phases 4-7. The intent of this post isn't to disagree with the CPC's forecast, but I think the two factors mentioned above should be followed closely as we head into the fall. It should be interesting!
Monday, June 22, 2009
Sunday, June 21, 2009
Friday, June 19, 2009
Thursday, June 18, 2009
Wednesday, June 17, 2009
Tuesday, June 16, 2009
Monday, June 15, 2009
Sunday, June 14, 2009
Friday, June 12, 2009
It does appear that Oktibbeha County will be clipped by the southern end of this bow echo after 7 p.m. The current thermodynamic environment does not suggest this derecho will lose strength anytime soon; in fact, the thermodynamic environment actually supports strengthening! However, this derecho is running away from stronger vertical wind profiles as it progresses further east. This indicates that the thermodynamic and dynamic environments across Mississippi are not as favorable for sustained maintenance as the environment across Arkansas. I expect a little but not a tremendous amount of weakening of the derecho as it plows across Mississippi in the next few hours. These extreme wind events typically take a few hours to wind down, especially given that a mature cold pool is present.
What can we realistically expect in Starkville and surrounding areas?
*The derecho will approach the area just after 7 p.m.
*A severe thunderstorm warning is almost guaranteed
*Wind gusts could exceed 65 mph
*Expect streets to be littered with small sticks and some larger branches; some trees may even be knocked down
*There could be many power outages across the county
**11:00 a.m. update to forecast: A well-organized squall line over Northeast Oklahoma will move to the southeast throughout the course of the day. It appears that this complex will arrive in our area by this evening and could bring a chance of severe weather to the area between 7-9 p.m. Damaging winds will be the primary threat with these storms.
Thursday, June 11, 2009
Wednesday, June 10, 2009
Tuesday, June 9, 2009
Monday, June 8, 2009
Thursday, June 4, 2009
Tuesday, June 2, 2009
Monday, June 1, 2009
Both forecasts suggest that there may be slightly higher than normal activity for named storms, but hurricane and major hurricane activity should be near normal. A developing but weak El Nino episode (check back soon for a future discussion on this) is cited as the main reason for an average year. Since El Nino has not truly developed yet, it's possible that the early part of the season could be more active than normal. This seems to be a common theme during years where ENSO-neutral conditions are present at the beginning of the season.
In fact, it appears that the middle to end of June could see an upswing in tropical cyclone activity as a Madden-Julian Oscillation pulse moves into the Caribbean. In the middle and later parts of the season, El Nino should be developed to the point that stronger than normal westerly upper level winds will be located across the Atlantic basin. This will enhance vertical wind shear, which will act to rip apart most easterly tropical waves. The tropical systems most likely to cause headaches for the U.S. in the middle to later part of the season are home brew storms that initiate from stalled frontal boundaries or upper level disturbances. Like my buddy Greg Nordstrom always says, it only takes one storm to make an unforgettable season. Most everyone will remember the 1992 hurricane season for Hurricane Andrew, but do you remember how many named storms there were that season? Only six. That's not to say that another Andrew will occur this year, but the point is that only one storm can make a season.