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Good evening everyone!
Bertha continues to the NNE at 21 mph, with maximum sustained winds at 50 mph. Satellite loop images and overlays indicate she may already be part of a frontal zone that has emerged off the U.S. East coast, and I believe extra-tropical transition may occur a little sooner than forecast. This will be my final update on Bertha
Elsewhere, not really much to speak of in the Atlantic basin. Water Vapor Loop imagery still shows plenty of dry air over the Atlantic basin.
Analysis of the Global models 12Z run does not indicate any development over the next 7 – 10 days. However, the GFS and ECMWF indicate an area with one closed isobar near the Cape Verde islands in about 10 days. Currently, they show no development of this feature. An interesting note however is, the African Monsoon circulation does nose out over into the Atlantic in about 8 days, and I cannot rule out a low in the area around that time frame into the forecast period. It should also be noted, that upper level winds are forecast to begin to become more conducive for development in about 10- 14 days…however with still an Easterly shear component, I wouldn’t expect to see anything really take off until approximately 40W or just past 40W. As I have stated in my previous forecasts, I really don’t foresee a decent uptick in activity beginning until possibly mid to late week of next week. Thus far, the season has pretty much followed climatology.
Analysis of EUMETSAT and SAL satellite imagery tens to indicate an increase in tropical wave activity, albeit nothing appears too impressive at the moment. One thing in favor though as far as these waves, the SAL satellite imagery indicates an increase in mid level water vapor, and sufficient water vapor in the upper levels of the atmosphere. In addition, we may be getting into that time where tropical waves could be getting stronger. We won’t however confuse this with an over active wave train, or stellar Cape Verde season. I will explain this thinking with a couple of the thermodynamic processes that occur, or don’t occur due to a couple of parameters.
In the current SST anomaly map, we are now seeing a decent cooling in the Gulf of Guinea of Africa
UNISYS SST ANOMALY MAP
A substantial cooling of the Gulf of Guinea indicates higher pressures over that area, which pushes the African Monsoon Trof or ITCZ further inland over the Western portion of Africa over the Western Sahel region. This allows for a shift in African rainfall, northward over the Sahel region, which allows for a reduction in SAL. This appears to be evident with the NHC TAFB Surface Analysis map showing the upward bow in the Monsoon Trof over West Africa. However this process may be just beginning, as with the higher pressures over the Gulf of Guinea, there is usually a shift in the SE trade-winds, in that they shift to a more southerly to SWLY direction. The SAL map also appears to show a reduction in the SAL at the moment. Anyhow, the cooling in the Gulf of Guinea creates a greater pressure gradient between the cooler SST anomalies, and the hot Sahara dessert. This increases the strength of the AEJ (African Easterly Jet), which has a tendency, or should have the tendency to strengthen tropical waves as they near the Western Sahel region.
Now, does this mean a busier Cape Verde Season? Not necessarily, as another factor comes into play here. Albeit tropical waves are a natural occurrence over the African continent from about a month prior to hurricane season until around the end of September, there is another entity at play which allows for a greater number of waves to occur. The IOD (Indian Ocean Dipole) which you have heard me mention before. This has to do with the SST Anomalies in the Indian ocean region. A positive IOD will aid in an increase of tropical waves, as it activates the Indian Ocean Monsoon, and allows for an increase in convection and rainfall off of the east African continent, to which some of this convection if it holds together, can move westward across Africa. So, as far as the IOD for this season, it is forecast to pretty much mimic last season in remaining neutral. This has been one of my main reasons in stating why I haven’t expected a booming Cape Verde season.
So based on all of this, and the projected OLR Anomaly forecast,along with what appears to be a slightly more favorable MJO forecast by mid month, hence my forecast for the increase of activity around that time.
I will continue to monitor the tropics for any significant changes or deviation to my forecast over the next 10-12 days.
I will have another update in the morning.
Have a blessed evening!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST / SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS
OFFICIAL SKYWARN SPOTTER (ADVANCED)