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(T. F. “Storm” Walsh III)
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STORM W’s SEASONAL HURRICANE FORECAST
TOTAL STORMS: 14-16
MAJ. HURRICANES: 3-4
MAJ. HURRICANES: 0
U.S. LANDFALLS: 2
UPDATE REGARDING TROPICAL DISTURBANCE HARVEY ISSUED 7:55 P.M. EDT:
I wanted to get something out this evening, as some things may be changing. It could be just some fluctuation in the guidance models because “HARVEY” is still not organized…however over the past 24-36 hours, statistical and dynamic model guidance have been trending with a more northern component on the future forecast motion of HARVEY. IT IS agreed in the global modeling that a weakness over the extreme NW GOMEX, and over NW TX to New Mexico is forecast to materialize. In addition, the mid to upper level low to the NW of HARVEY is adding to this.
MODEL GUIDANCE TREND FROM 00Z 21 AUG to 18Z 21 AUG
Disregard the storm name KENNETH
Based on analysis of a few items, the GFS still indicates a very favorable upper level pattern in the GOMEX as HARVEY heads toward land.
GFS 18 Z WIND SHEAR FORECAST
Current intensity modeling still indicates a probability that HARVEY could attain Category ONE Hurricane status just prior to landfall. The most accurate of the intensity guidance has backed down some, with two of the models indicating a system just at CAT 1, and another at 80 mph. The fourth indicates a strong Tropical Storm.
Based on the dynamic guidance trend northward, and a shift in some of the global models to the north (even though all of this could change somewhat), I recommend at the moment, residents from Brownsville Texas, to Matagorda Bay monitor this system closely, for any significant changes that may occur. Given the uncertainty that still remains in forecast track and strength, I am waiting to see what occurs with model guidance once the system enters the GOMEX, and comes under the influence of the upper level anti-cyclone which is forecast to remain with the system. Exact strength and track will depend on where and when the system enters the GOMEX, and how well it survives the Yucatan Peninsula.But in the meantime, to err on the side of safety, residents along the Texas coast in the areas I just mentioned, should review their preparedness plans and ensure your supply kits are in order.
IF I do not update late tomorrow evening, I will try for Tuesday evening, as I work the next 5 days.
Good day all!
Forecasting the 2 current systems has been rather difficult, due to the fact in that the tools I use for analysis, keep showing changes in various parameters from run to run on various models, such as forecast steering layers, wind shear values, and the upper level wind pattern…not only in terms of a few days, but almost on every 6 – 12 hourly run. There doesn’t appear to have been any type of consistency to work with. This is why you keep seeing a change in forecast track and a change in the written synopsis. I can only forecast as good, as the information I have to analyze. I’m sure some of you are familiar with the term GIGO…(Garbage In…Garbage Out). With that being said:
As of the 2:00 p.m. TWO from the NHC, the remnant of HARVEY was designated at a HIGH (90%) probability of regeneration and cyclone development during the next 5 days. INVEST 92L has been designated as having a MEDIUM (40%) probability during the next 5 days.
I’m going to switch the order, and focus on the nearest threat to the U.S.
INVEST 92L was located in satellite imagery, just around the central Bahamas. As of the 12Z ATCF BTK report, the following was available on INVEST 92L
8:00 AM EDT Aug 21
Location: 24.1°N 74.1°W
Moving: WNW at 20 mph
Min pressure: 1013 mb / 29.91 in
Max sustained: 30 mph
Satellite loop imagery indicates the system is still disorganized. However, the last couple of frames in the loop tend to indicate 92L may be slowly trying to make a come back.
Analysis of the current wind shear product from CIMSS indicates that shear has relaxed around the system. As of the 1500Z update to the shear product, an upper level anticyclone may be trying to develop over the system. Based on the current shear forecast, the GFS does indicate somewhat improving upper flow, and the Tropical Cyclone Diagnosis modeling still indicates shear magnitude to fall to 10 kts or below for the next couple of days.
Analysis of water vapor imagery indicated 92L has been fighting drier air to the NW, however analysis of current OHC indicates 92L is heading for some high Ocean Heat Content, which may allow a better mixing out of the dry air.
CURRENT OHC MAP
Based on this analysis, INVEST 92L may have a slim chance at becoming a Tropical Depression, and could make landfall in Florida, which seems to be a higher probability based on analysis of this mornings global model analysis and track guidance.
Current intensity models tend to indicate this.
92L INTENSITY FORECAST
INVEST 92L is currently moving to the WNW, and I expect this motion to continue through today. However, based on the forecast steering layers maps, a slight bend to the west may occur, briefly, which would bring the system to the Florida coast in about 24-30 hours. The majority of model guidance and EPS members do indicate this. Thereafter, they system may meander or stall for a breif period, before recurving toward the NNE or NE, and may ride just offshore the U.S. East Coast. The ECMWF Cyclone Probability model indicates 92L could then become a Tropical Storm by day 4 and 5 in the period as it moves to the NE. Based on my analysis, and current intensity guidance, I cannot rule this out at the moment.
92L DYNAMIC GUIDANCE
I will continue to monitor this system closely.
Elsewhere, the remnant of HARVEY continues to move through the Caribbean, and is approaching the Yucatan Peninsula / Belize area
As of the 12Z ATCF BTK report, the following was available on the remnant, or Tropical Wave “HARVEY”
8:00 AM EDT Aug 21
Location: 16.3°N 82.3°W
Moving: W at 20 mph
Min pressure: 1008 mb / 29.77 in
Max sustained: 30 mph
Current satellite loop imagery hasn’t shown much change in organization of the system.
Based on the wind shear forecast from the GFS, and most recent wind shear product, an upper level anticyclone has prevailed over “HARVEY” for the past 12- 18 hours.
HARVEY WIND SHEAR
This is what led me to believe that the system would have bounced back to at least depression status by now. However closer analysis and thought reveals 3 hindering factors at the moment. A little bit of drier air has been affecting it, indicated by some small outflow boundaries, forward speed, and proximity to land. Now comes the tricky part in the forecast…we are going to have to wait and see, what is left of this system, after crossing the Yucatan Peninsula, and entering the BOC. Now, I want to caution you on this, based on the modeling has not been too consistent regarding intensity issues. Based on what we (in the tropical weather community) know, in most cases, a weaker system, especially entering the GOMEX, will be able to comeback quicker, than one which is stronger. I like to use the analogy from Joe Bastardi, in that looking at it from a perspective of calories. Say a system like HARVEY has 200 calories, and the GOMEX has 1000 calories…that system will gain another 800 calories. A stronger system, say with 800 calories, is not going to gain much. With that said, based on the wind shear forecast, BOTH the GFS and ECMWF maintain an upper level anticyclone over the system for the duration.
GFS WIND SHEAR FORECAST
The GOMEX has some moderate heat content which may aid in strengthening. At the moment, the GFS and ECMWF only bring it to low end tropical storm strength. This seems a bit unusual given the shear forecast. The only thing I can touch on is, RH at the 700 and 500 mb levels does tend to indicate drier air on the west side of the system, which may be why both models are keeping the system weaker at this time.
Intensity guidance models do want to bring this to borderline CAT 1, to low end CAT hurricane status by day 4-5, which based on track guidance, would be just at landfall. My best advice is we need to continue to monitor this system for any significant changes to the pattern, and steering.
HARVEY INTENSITY GUIDANCE
The remnant of HARVEY is moving to the WNW, and I expect this motion to continue during the next 48 – 72 hours. Thereafter, based on forecast steering, and model guidance, a weakness in the ridge begins to occur in the extreme NW GOMEX to WNW of TX. At that time, a bend or turn to more of a NW fashion should occur. This appears to be the consensus of most of the guidance models. However once again, we are working with a disorganized system. Track guidance should improve once the models pick up on the system in the GOMEX. The majority of the guidance, as well as the current GFS track, bring this ashore at, or just slightly south of Brownsville TX. The only dynamic consensus model in the recent run, the TVCA, brings it south of Brownsville, and mimics the current ECMWF track. Again, this shows you how track guidance can change so quickly. Two days ago, model guidance had this going into Mexico, and now look at the change.
HARVEY EARLY TRACK GUIDANCE
The bottom line…residents along the south Texas coast, mainly Brownsville at the moment, should monitor the progress of this system closely during the next 72 hours. I cannot safely for sure say this may not be a hurricane by landfall at this time. Given that, please take this time to review your preparedness plan, and check your emergency supply kit. Regardless of development, IF this system makes landfall close to Texas, be prepared for heavy rainfall and possible local flooding.
The following is the WPC total precipitation forecast for the next 7 days.
WPC QPF FORECAST (CLICK FOR LARGER IMAGE)
I am posting the follow NWS Hazard and Warning map in the event I am not able to update. IF this system strengthens and threatens the Texas coast, my intention is to update everyone after I get home from work during this week. It will be a very late evening update however.
Elsewhere…I am not expecting tropical storm development during the next 5-7days.
Have a blessed evening!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS