The Return of Bertha - FLHurricane.com

FORECAST POSTED: 8/12/02/ 9:30 PM EDT

Tropical Weather Outlook:

For the third straight day, the Gulf of Mexico is full of convection. We aren't concerned about the convection in the western gulf at this time. The convection in the northwest Gulf is associated with an upper level disturbance and a surface trough. However, the central Gulf states will continue to see a large amount of rainfall over the next few days. The southerly flow from the Gulf of Mexico will continue as a frontal boundary over Kansas (The same system causing the severe weather) drops south.

The eastern Gulf of Mexico disturbance is more interesting. Now we aren't forecasting development from this disturbance in the Gulf of Mexico. Sea level pressures are way too high to sustain development and the convection is very disorganized. But some of the models take the low northeast. This is reasonable since the disturbance will likely move north, over the western edge of the western Atlantic ridge. The track would be right along the east coast from Georgia to North Carolina. The center will then move out into open waters. But the system won't just move straight out to sea. A ridge to the north of the disturbance will then begin to build in, slowing down the easterly movement. Now this is when we will have to watch this one for development as the center will still be over 80 degree water temperatures. We wouldn't be talking about a purely tropical system anyway. I would have to say chances of development are about 10%. The chance for development will slowly increase if it continues to follow the forecast path and if it holds together.

Our second disturbed area is north of Puerto Rico. Earlier today and yesterday,we had a possible closed low. Now the system appears to be more like an elongated broad area of low pressure. The northern extent of the trough will likely fizzle. The southern end is what we will have to watch. The broad low will continue on a west to west-northwest track over the next few days. Conditions out ahead of the low are becomign increasingly favorable for development as an anticyclone in the upper levels is developing over the Bahamas. Currently, convection is decreasing and it appears tha the system is falling appart. Now we have to wait and see if the convection refires later tonight or tomorrow. If not, then this broad low is history. As for the forecast path, the center should pass over the Florida Keys in 72 hours. This would take the system into the eastern Gulf of Mexico. If the low can survive the next day or two, the Gulf states could be in for some trouble. But the next couple of days are the key. Since the low has become more elongated and the center has become ill-defined, I have lowered the chance of development down to 10%. Now if we can get the convection to refire, I will become more concerned.

The third area is a tropical wave near 35W. Both the MRF (GFS) and AVN models have been forecasting development from this wave. However, the latest run no longer suggests development. Therefore, a more westerly track towards the islands is being forecasted as the wave will not be controlled by winds in the upper levels. Development from this wave wasn't forecasted to begin with and this appears to be verifying. There is still a lot of sinking air over the central Atlantic that should hinder any chances of development.

The next significant tropical wave is located over western Africa. We will have to wait and see what this wave does once it emerges off the coast to see how it interacts with water for the first time. The wave should quickly fizzle as the east Atlantic is still being dominated by subsidence. But the center of circulation should still be monitored as it will slwoly move into warmer waters.

The Caribbean Sea is being dominated by strong westerly winds. There is a very weak tropical wave located along 75W but there is barely any convection associated with it. The Caribbean Sea won't sea much in the way of development at least through Wednesday.

There is an upper low east of New England. This low is not warm core and is nontropical. In addition, there are no signs of this low becoming tropical in nature. The low shouldn't move much over the next 12 hours before picking up speed and racing east-northeast.

NOAA And Dr Gray's Updated Seasonal Forecasts...

Dr. Gray: 9 named storms, 4 hurricanes and 2 major hurricanes

NOAA: 7-10 named storms, 4-6 hurricane and 1-3 major hurricanes

Both NOAA and Dr. Gray do have some good points for downgrading their seasonal number. However, there are many points that I also disagree with. Both NOAA and Dr. Gray mentioned cooler than normal sea surface temperatures across the Atlantic basin inhibiting development. This doesn't appear to be the case. We have average to slightly above sea temperatures across the Gulf of Mexico and the Caribbean Sea. The sea surface temperatures along the east coast are even warmer...as warm as six degrees above average in some areas. The eastern atlantic is the only area that is experiencing cooler than average SSTs. But you have to notice that the bulk of the cooler sea temps are north of the Cape Verde islands and the Mean Development Region (MDR). So even the negative SSTs in the eastern Atlantic shouldn't have much of an influence on activity. Even if the sea surface temperatures were to have an impact, the impact would be that tropical waves moving off of the African coast would deelop closer to land. This could mean trouble as the majority of the systems that do form in the east Atlantic easily get forced north by troughs.

Sea surface temperatures have been on a warmign trend over the past five weeks. I mentioned that the temperatures would continue to warm a couple of weeks ago. I also mentioned that this was in response to the North Atlantic Oscillation turning negative. The NAO has gone positive for a short period of time. However, long range model guidance is forecasting the NAO to turn NEGATIVE for a second time. All this means, is that the current warming trend should continue.

The main reason why they lowered their forecast numbers was because they believe that El Nino will enhance the westerly winds across the Mean Development Region. First of all, El Nino is weak.I agree with them that we will likely see a moderate El Nino by January. However, the sea surface temperatures in El Nino regions 1 and 2 are still running normal to slightly below normal. El Nino regions 1 and 2 are the 2 most important regions when it comes to Atlantic activity. Now there is an El Nino folks. If you look at the central Pacific, you will notice a large swath of above normal sea surface temperatures. In addition, the cool anomolies are now beginning to moderate. So we are definitely in a developing El Nino stage. However, it takes at least three months for El Nino to begin having any affects on the westerlys across the Atlantic. So El Nino should remain weak throughout the remainder of the season. Therefore, the influence on seasonal activity by El Nino should be weak. But wait there is more!

The negative phase of the Madden Julian Oscillation (MJO) will likely be centered over the Atlantic basin during the climatological peak of the Atlantic hurricane season. The negative enhances tropical activity. The activity is enhanced because the negative usually causes vertical wind shear to decrease. So we have a weak El Nino expected to cause the shear to increase while the negative phase of the is expected to be over the Atlantic at the same time. The negative is one of the main reasons why I don't believe El Nino will have a major influence on the remainder of the season.

Another thing that I also wanted to mention, is the fact that El Nino could actucally enhance activity in late October and into the month of November. Typically during El Nino years, we see above average subtropical activity. We saw a lot of subtropical activity in the early part of the 1997 season. In addition, long range model guidance indicates that sea level pressure over the western Atlantic will be below average. I can believe this since we're already seeing negative SLPA over the west Atlantic. El Nino should have a slightly greater influence by November. By then, the bulk of tropical activity should be over with. But this doesn't mean anything for subtropical activity. We could see a few subtropical storms off the east coast towards the end of the season.

FORECASTER: Jason Moreland, TWWFT

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DISCLAIMER: THIS IS NOT AN OFFICIAL FORECAST. PLEASE LISTEN TO YOUR LOCAL NEWS OR THE National Hurricane Center FOR THE LATEST INFORMATION.

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