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Good morning everyone!
Tropical Disturbance INVEST 99L remains disorganized this morning. Based on the 06Z ATCF tracking update, the following information was available regarding INVEST 99L:
LOCATED: 17.6N…87.1 W
MOTION: WNW 12 MPH
MAX SUSTAINED: 30 MPH
PRESSURE: 1009 MB / 29.80 IN.
Albeit this system is currently disorganized, the lower level circulation is a little easier to define in satellite loop imagery.
Based on analysis of the current wind shear product from CIMSS, INVEST 99L has been under about 20 knots of northerly wind shear. However, the disturbance is now moving into an area where shear has been on the decrease over the past 24 hours.
The most current wind shear forecast indicates zonal shear will begin to subside today as this disturbance begins to cross into the Yucatan Peninsula. Upper level winds are forecast to become more conducive for further development in about 12 hours. Based on this analysis, some better organization should begin once 99L enters the BOC / SW GOMEX. Once in the SW GOMEX, this system will have to be monitored closely.
Based mainly off analysis of current steering, INVEST 99L continues toward the WNW. This motion is also noted in satellite loop imagery, although given the ambiguity near and around the “center”, satellite imagery may indicate just a slight more westward component.
CURRENT STEERING LAYER MEAN
The NHC has designated a MEDIUM (50%) probability of tropical cyclone formation with INVEST 99L during the next 5 days.
Based on analysis of the steering layers forecast maps from the PSU e-WALL tropical site, valid for 12Z today, I expect the WNW motion to continue today, with a slight bend toward the left as the disturbance enters the BOC, due to ridging being reinforced to the north over the Gulf coast states area at the moment. For the most part, this should continue into Mexico as forecast. However, in past experience as a forecaster, systems that enter into the BOC need to be monitored carefully, as in my past experience with these BOC systems, as the disturbance crosses the Yucatan Peninsula, the low level circulation will become somewhat disrupted, and as it enters the BOC, a center relocation/reformation will most likely occur. Some of these systems in the past, have had center re-locations further north. Generally, a center reformation will occur under where the heaviest convection develops. The reason I say it will need to be monitored closely for this is, should the center relocate too far north, it could pickup the steering flow that is shown in the blue arrows, vice the flow it is in right now, shown by the pink arrows.
Unfortunately, Dynamic Model guidance is scant at the moment.
The second thing which needs to be monitored is, if the upper level winds are favorable, systems this time of year have a tendency to ramp up a little quicker in the BOC, due to the shape of the coastal land mass. As air flows counter-clockwise around the disturbance, this area helps force air toward the center of the system…what we call forced convergence. This aids in a steadier ramp up of these type of systems.
I will continue to monitor this area closely over the next 72 hours for any significant changes and may post an update sometime this afternoon.
Elsewhere, the area in the CATL I have been monitoring has lost much of its structure. The culprit…DRY AIR!
Currently, upper level winds are conducive for development, and are forecast to remain conducive during the next 24 – 30 hours, when thereafter, this area will encounter some strong westerly shear.
I will continue to monitor this area, however development doesn’t seem likely at the moment, given the wind shear forecast. In fact, anything coming off the coast of Africa over the next 5 – 7 days is going to have to remain at, or just below 10 degrees latitude to avoid wind shear.
Have a blessed day!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST / SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS
OFFICIAL SKYWARN SPOTTER (ADVANCED)