TROPICAL CYCLONE FORMATION: INVEST 99L (60%) / T.D. FIONA / T.S. GASTON
Disclaimer: This site is not affiliated with the National Hurricane Center, Storm Prediction Center, or National Weather Service. ALL forecasts herein are the result of my analysis, and I am solely responsible for the content.
(T. F. “Storm” Walsh III)
For those who have donated to my site, your help has been greatly appreciated. For those not aware, donations to my site help me offset my personal out of pocket expenses…such as some of the model maps you view on here, are only available due to my subscription to the corresponding site. The F5 Data maps I post, also another out of pocket expense (monthly subscription). Updates to software (weather related), and costs for my domain name are also out of pocket to me. To donate, please click the DONATE button to the right. Any help you provide is immensely appreciated! Although it may seem I am not here and working in support of your donation, I have to work my forecasting time around my ever changing work schedule.
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!
Wanted to briefly mention FIONA and our new Tropical Storm GASTON: FIONA is barely holding on as a depression, and is forecast to slowly weaken into a remnant low.
Gaston is forecast to become a Category 1 hurricane in 24 hours at 75 mph, and strengthen to almost a top end CAT 1 by 48 hours. Since neither of these systems is a threat to land right now, please visit the NHC website for more information on these systems.
Tropical Disturbance INVEST 99L is still fighting off a bit of drier air this morning, noted by some outflow boundaries north and west of the system in RGB satellite loop imagery.
NHC has designated a MEDIUM (60%) probability of development during the next 5 days.
As of the 12Z ATCF BTK product, the following was available on INVEST 99L:
8:00 AM AST Tue Aug 22
Location: 16.4°N 56.5°W
Moving: WNW or just north of due west at 17mph
Min pressure: 1009 mb / 29.80 in
Max sustained: 35 mph
Satellite imagery indicates thunderstorm activity has become sporadic over the past few hours, with convection waxing and waning at various locations within the system.
Based on the 12 hours average from 00Z yesterday evening, to this morning’s ATCF product for 12Z, and current satellite loop imagery, the average motion appears to be to the WNW or, just north of due west. It is difficult at the moment to locate an actual “center” on satellite, but based on the current forecast steering layers product from CIMSS, 99L should continue on a general WNW motion. Based on the recent Multiplatform Tropical Cyclone Surface Wind Analysis products, 99L still lacks a closed surface circulation. This tends to make model guidance somewhat inaccurate, however given what I have to work with based on model guidance, and current forecast steering layers maps, I expect 99L to continue in a general WNW motion for the next 72 – 84 hours with a slightly more north component, as a large break in the subtropical ridging occurs between the eastern U.S., and Bermuda. This may cause 99L to slow its forward motion, and possibly, briefly stall. Thereafter, the steering layers forecast maps indicate the ridge I have been speaking of, will slide to the east, and build to the north of the system. From there, the exact track is hard to pinpoint at the moment, as again, modeling is working with a system in which they have no LLC to initialize. Based on the steering forecast however, and along with the 12Z Dynamic model guidance, a bend to the left seems in order, and I am currently inline with the TVCN / TVCC consensus models the way the track looks, (as far as motion) however based on current satellite motion of 99L, I am currently just south of that. Based on this, and current steering layers forecast, it may be possible the dynamic models could shift further left in the next couple of runs. Regarding this, and future track, will depend on how organized or disorganized the system becomes. As it looks right now, based on analysis of the global models, and forecast steering, the consensus appears to be this will be a Bahamas/Florida threat in a few days. There is disagreement in the modeling as to whether or not this threatens the east Florida coast and crosses over, if it threatens south Florida, then goes into the GOMEX to become a threat to the Big Bend area of Florida, or if it rides along the U.S. east coast. The biggest discrepancy appears to be between the ECMWF operational model, and the ECMWF Ensemble members. Given the uncertainty in the models, and lack of good initialization with the system, I cannot give you an exact pinpoint location as to which area will definitely be threatened.
As I mentioned, the satellite appearance of 99L appears somewhat ragged. This is due partially to some amount of dry air ingestion, and upper level winds not being exactly optimal, as the current upper level anticyclone is displaced slightly to the west of the reported center location, causing some slight shearing effect. However, in the last couple of loop images, there appears to be the start of upper level clouds fanning out over the north and south areas of 99L. Based on the current shear product from CIMSS, there may be around 20 knots of NW shear over the NE portion of 99L.
The current wind shear forecast from both the GFS and ECMWF tend to indicate somewhat of a favorable upper level pattern regarding the 200 mb streamline pattern, with the ECMWF being more forgiving. At the same time, information from the NOAA RUC HFIP product page indicates modeling, especially the GFS, to keep wind shear averaging around 8-10 knots over the next 4-6 days.
99L is still in some direr air, but based on water vapor loop imagery, maybe not as much as yesterday. 99L is still in an environment of high TPW values, and will soon be moving over an area of higher OCH (Ocean Heat Content). As a rule of thumb (and as I have witnessed in some past systems), the combination of TPW and higher OHC should be enough to allow 99L to mix out the drier air.
Based on this, and the forecast, what appears to be a favorable upper pattern during the next 5 days, I still cannot write this system off. IF 99L is able to close off a LLC, I believe at this time, it may be able to continue some slow organization and strengthening. IF this comes to fruition, I believe the real show will occur as it enters the central Bahamas, in a more steady pace of strengthening. As we know, all of this is subject to change, and I can only put to you what I have learned in my past experiences, with the current and forecast information. The ECMWF still insists on bring this over south FL. in 6 days, then to the Big Bend region as a strong hurricane, while the GFS is not so interested, and keeps it a weak system, over the Florida straits and into the FL. Panhandle. The current intensity guidance still shows the 3 models widely used for intensity forecasts, bring 99L to hurricane status. I have the 3 intensity models circled for you.
Based on these analyses, residents of the Bahamas, and Florida peninsula should monitor this system closely if development occurs in the southern Bahamas during the next 4 – 5 days.
I should have another update tomorrow, albeit not sure of the timing.
Have a blessed day!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS