TROPICAL CYCLONE FORMATION: INVEST 99L (80%) / T.S. GASTON
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(T. F. “Storm” Walsh III)
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CURRENT 2016 ATLANTIC TROPICAL CYCLONE TOTALS:
TOTAL STORMS: 7
INTENSE HURRICANES: 0
StormW’s Seasonal Hurricane Forecast:
TOTAL STORMS: 13-15
INTENSE HURRICANES: 3-4
Good day everyone!
This is a SPECIAL UPDATE on INVEST 99L:
As of the 18Z ATCF BTK report, the following was available on INVEST 99L:
2:00 P.M. AST Wed Aug 24
Location: 18.7°N 65.4°W
Moving: WNW 22mph
Min pressure: 1009 mb / 29.80 in
Max sustained: 45 mph
The disturbance is moving to the WNW at around 22 mph, and I expect this motion to continue for the next 2-3 days.
A analysis of current satellite imagery loops indicates that the “center” may ave decoupled and took a slight jog northward. This would explain the almost 2 degree shift north of the reported center since 12 hours ago.
Satellite imagery indicates a somewhat sheared system, which would correlate with the latest wind shear product from CIMSS, showing some pretty moderate shear over the system, as the upper level anticyclone is now centered SW of the center of 99L. This is allowing the the north and eastern portion of the upper level feature to bring shear across 99L form the west and NW, pushing convection away from 99L at the moment. Based on my earlier synopsis (below), this was pretty much called for in the forecast, but appears to have occurred much earlier than planned. The updated wind shear forecast from the NOAA RUC HFIP site (12Z) now calls for this increase in shear to remain for the next 24 – 30 hours, and for it to begin to slowly subside from 42 hours, and beyond, with the GFS re-establishing the upper level anticyclone in 96-120 hours over the Bahamas, and the ECMWF a little quicker in 72-78 hours. As I stated earlier, this has a little bit of a battle ahead of it. Again, if it survives this round of bad stuff, we should see development in the Bahamas. It still has good TPW associated with it.
A couple reconnaissance flights today still did not locate an organized, closed LLC.
NHC still indicates an 80% probability of cyclone development
Speaking of this, do you remember from the synopsis this morning, I mentioned model guidance (both intensity and track) should be considered preliminary, as there was no closed LLC for the models to latch onto for initialization and tracking, and how I always mention that the steering pattern can change quickly? Well, case in point, and another teaching point for you, my clients. The 18Z Dynamic model guidance, now indicates a track right over the Florida peninsula, having shifted back to the east from this morning. Remember the ECMWF model, indicating a CAT 3 Hurricane into LA? Well, it’s track has shifted extremely east, and over my area with a minimal T.S.
This is most likely in response to the updated steering forecast maps, that now indicate the ridge that builds over the Mid Atlantic states, doesn’t remain as strong through the period, with the center of the ridge shown now retrograding back slightly toward the west, allowing for a slight blocking motion for a direct west to WNW motion, as this setup opens the weakness in the ridge more, NE of Florida…so the resultant flow is more of a WNW motion for the next 3-4 days, with a turn now more to the north thereafter, as indicated in the 18Z Dynamic guidance.
So, the moral of this story on this system, is, to quit trying to figure out where it may go, and continue to monitor the system in real time, as until this system develops a well defined, closed LLC, we will continue to see this “windshield wiper effect” in the model guidance.
Have a blessed evening!
First off…some may wonder as to why all tropical systems may not be included in the synopsis, when there are multiple systems in the Atlantic. My preference is to issue quick access to the information on systems far out int he Atlantic, that have no immediate threat to land massed over the 5-7 day time frame in the forecast period. My main focus is placed on systems that may pose a threat to our friends in the Caribbean Islands, Mexico, the Bahamas, and CONUS. Bermuda will also be included in mention within the synopsis if a threat is established.
With that said, information on Tropical Storm GASTON may be found at the NHC website. Please click on the following graphic which is linked.
SPECIAL TROPICAL WEATHER OUTLOOK FROM NHC:
Updated: An Air Force Reconnaissance aircraft currently investigating the broad low pressure area and tropical wave near the northern Leeward Islands has found winds to tropical storm force in a few squalls near the northernmost Leeward Islands. Squalls to tropical storm force can be expected over the extreme northern Leeward Islands and portions of the northern U.S. and British Virgin Islands this afternoon. The reconnaissance aircraft mission is ongoing to determine whether or not a tropical cyclone has formed.
Although environmental conditions are currently only marginally conducive for additional development, this system could become a tropical depression or tropical storm at any time during the next few days while it moves west-northwestward at about 15 mph across the northern Leeward Islands, near or over Puerto Rico, Hispaniola, and the Bahamas. Strong winds, heavy rains, and possible flash floods and mudslides are expected to occur over portions of the Leeward Islands, Puerto Rico, Hispaniola, and the southeastern and central Bahamas. Please consult products issued by your local meteorological offices for further details. Interests in the northwestern Bahamas and Florida should also monitor the progress of this system. * Formation chance through 48 hours…medium…60 percent * Formation chance through 5 days…high…80 percent
$$ Forecaster Brown
Tropical Disturbance INVEST 99L had become better organized overnight, as far as overall cloud and thunderstorm structure. Indications from the NHC and MTCSWA site indicates 99L still lacks a well-defined LLC. Analysis of the surface wind data from MTCSWA indicates the lack of a true westerly wind on the southern side of the center, or a very light westerly flow (5 knots). The circulation appears to remain somewhat broad as well. The NHC has increased the probability of tropical cyclone formation to MEDIUM (60%) over the next 2 days, and to HIGH (80%) during the next 5 days.
Recent satellite loop imagery indicates the system, albeit convection seems consolidated, has deteriorated slightly in over all structure. Based on analysis of the recent wind shear product and water vapor loop images, as well as RGB satellite loop images, 99L is currently under conditions that are marginal right now. Some dry air intrusion was detected in my analysis, by the presence once again, of some small outflow boundaries west and north of the system. However, not to sound like a broken record, on the current and forecast path, 99L should be entering some slightly higher OHC later today. 99L is also under some slight wind shear once again on its NE quad, due to its relation to the position of the upper level anticyclone. Looking at satellite loop imagery, and updated upper level wind pattern, it does appear the outflow channels may be getting better established. Earlier this morning, the outflow seemed disrupted (0600Z), but showed a nice improvement in the 0900Z product.
Based on analysis of forecast wind shear products form both the GFS and ECMWF, the upper level anticyclone may remain with 99L for at least the next 36-48 hours, before collapsing. So, there could be more slow organization of the system within that time. However, although this feature may collapse, indications are wind shear values may relax substantially after that, and is indicated in the NOAA RUC HFIP product by the 2 available models at analysis time…the GFS and NAVGEM.
Based on analysis of these parameters, I am calling for further slow organization of 99L, although it’s not to say that development may be a struggle during the next 36-48 hours, until we see if forecast conditions come to fruition. Based on current dynamic model guidance as far as estimated track, I do believe once 99L enters the Bahamas area, development may become more gradual, as both the GFS and ECMWF indicate the upper level anticyclone becomes re-established over the system, with the ECMWF indicating a well established, textbook upper level anticyclone. By this time as well, 99L will be over some extremely high OHC. Should 99L survive the struggle next 2-3 days, as I stated, the system should begin to develop quicker, and could become a Tropical Storm prior to possibly crossing the southern tip of Florida, or entering the FL. Straits.
There are various scenarios laid out by the models on future strength from a weak system remaining over FL in 6-8 days, to a CAT 3 Hurricane in the GOMEX. This will be addressed below.
As of the 8:00 a.m. ATCF BTK product, the following was available on INVEST 99L:
8:00 AM AST Wed Aug 24
Location: 17.7°N 63.2°W
Moving: WNW 17mph
Min pressure: 1009 mb / 29.80 in
Max sustained: 35 mph
The disturbance continues to move to the WNW and I expect this motion to continue for the next 48-60 hours, with a turn more toward the Bahamas thereafter, based on current forecast steering layers maps. 12Z Dynamic guidance indicates models have shifted once again, slightly to the left.
Based on analysis of current forecast steering layers map, the model guidance seems plausible at the moment. Track guidance will become a little more accurate once a closed low level circulation can be established and initialized.
Analysis of the global models indicates various scenarios as I mentioned. The GFS keeps 99L an open wave in the Bahamas, then brings it west through the FL Straits, then back over FL. as a week low at around day 7-8 in the period. CMC GGEM keeps the system along the FL east coast, and brings a T.D. into around West Palm Beach, weakens it as it crosses FL., then shows T.S. making landfall near LA/MS border. The ECMWF is the one that scares me, as it develops a T.S. in the extreme northern Bahamas in 96 hours, bring it through the FL. Keys, then into the GOMEX, where it develops a Hurricane rapidly by day 6, and brings a CAT 3 Hurricane to landfall near TX/LA border. At the moment, it’s somewhat difficult to determine which one is correct. However, as much as I hate to, until we see what actual conditions will be in a few days, I have to lean slightly more toward the ECMWF solution. If you recall, for the past 3 -4 days, the ECMWF has been persistent in the left shift of the track forecast, and has not backed off on the CAT 3 Hurricane solution. Based on my analysis of the forecast steering maps, I kinda have to rule out the GFS solution, as by that time in the forecast period, the ridge forecast to build north of the system, is still in place, which would tend to keep a more westerly component to the system. If the wind shear forecast comes to fruition, especially if the ECMWF is correct with the upper level anticyclone forecast, I cannot totally rule out its current solution and would be foolish to tell you it definitely won’t happen, especially given the OHC in the central GOMEX. However as I always reiterate, the models should be considered preliminary and as an approximation at the moment. ONCE a LLC is closed off, and we see progression in development, then guidance can be relied upon more readily. In any event, with the analysis of forecast steering maps, and continued shift left with the dynamic models the past 2 days, this appears as that whatever 99L becomes may very well be a GOMEX event. This is not to scare anyone, however the person I learned a lot from on tropical forecasting, Meteorologist Joe Bastardi from Weatherbell analytics,is also discounting the GFS, and mentions in his column, that should 99L survive and enter the GOMEX, the track is good for it to ramp up very quickly. From his column yesterday:
The western scenario that we have had with 99L is in the ballpark. We don’t want to change anything yet, but we continue to emphasize that this can explode, a la Joaquin, especially after the westward turn is made. This is why we keep bringing it to a Category 3, as long as path is over the water.
Let’s watch it closely, but given the major ridge over the Mid-Atlantic, the Andrew/Katrina/Ivan blend looks reasonable. I like our ideas on intensity but understand that the western option is on the table.
I would trust the Euro much more than the GFS, which doesn’t even have a storm. This is several runs in a row that the Euro blows this up from Bahamas on in, though the track is questionable.
Again the westward turn after the northwestward motion is a known rapid intensity feed back because it signals an improvement in outflow relative to the ridge. The change of pattern in relation to the storm is huge in these sudden development cases.
I will be monitoring this system closely over the next few days, but won’t be able to update again until Sunday. This should put the system somewhere over the Bahamas…so, by then, I should pretty much know what may occur. Residents of the Leeward Islands, Puerto Rico, Hispaniola, and the southeastern and central Bahamas should closely monitor this system. Interests in the northwestern Bahamas and Florida should also monitor the progress of this system.
Have a blessed day!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS