Good day everyone!
Things have changed over the past 24 hours in regard to conditions forecast for the upper level wind pattern. Analysis of the current wind shear pattern shows a big shift in the upper level anticyclone we saw over INVEST 92L during the past 12 hours. As a result, the upper level feature is over the Yucatan Peninsula, in turn placing 92L under about 15 knots of mid to upper level shear. This has caused the disturbance to become less organized overnight, however current satellite loop images indicate an increase in thunderstorm activity once more, and the system may become just slightly better organized prior to crossing into the Yucatan Peninsula. The NHC has changed the probability of this becoming a tropical cyclone during the next 48 hours to MEDIUM (50%), with a HIGH chance (60%) over the next 5 days.
NHC GRAPHICAL TROPICAL WEATHER OUTLOOK
The disturbance continues to move toward the WNW, and I expect this motion to continue today into tomorrow, with more of a track toward the NW to NNW once it emerges into the GOMEX. Based on the 12Z dynamic model guidance, I prefer a blend of the TVCN and OFCI track at this time, based off of the current run of the PSU e-WALL forecast steering maps.
As far as strength, once this disturbance enters the GOMEX, the current wind shear forecast from the GFS indicates only a small window of opportunity for further organization, as upper level winds become more conducive in about 24 hours through 36 hours. Thereafter, upper level winds are forecast to become marginal at best. Given these parameters, it now appears this my struggle to reach depression status in the GOMEX, and at the moment, I would have to agree with the GFS and FIM Experimental model at this becoming an open wave prior to affecting the Gulf Coast states. The CMC I believe is too over zealous in developing a tropical storm. However, as a caution, one does not turn their back on a system in the GOMEX in that as quickly as we have just seen the forecast pattern change to less favorable upper level conditions, it could as easily change the other way. Remember, this current change happened in less than 24 hours. I have included the 96 hour accumulated rainfall map from the FIM model. Regardless of development, residents along the Gulf Coast from LA to AL should be aware that a flooding potential exists.
I will continue to monitor this disturbance for any significant changes.
Tropical Low INVEST 93L has been upgraded to Tropical Storm Erin…our second Cape Verde system of the season. Satellite loop imagery indicates cloud tops over the LLC have cooled, and a CDO is developing, along with banding features.
As of the 11:00 a.m. EDT advisory from the NHC, the following was available on Erin:
11:00 AM AST Thu Aug 15
Location: 14.4°N 26.5°W
Moving: WNW at 15 mph
Min pressure: 1006 mb / 29.71 in
Max sustained: 40 mph
Based on analysis of current wind shear, a textbook upper level anticyclone is centered directly over Erin at the moment. The wind shear forecast indicates upper level winds to remain generally favorable during the next 72-96 hours, and further strengthening should occur.
The forecast discussion from the NHC 11:00 a.m. advisory indicates Erin to traverse waters of 26-27C over the next few days, so I am calling for slow strengthening than per NHC forecast discussion, as a stable stratocumulus deck lies just NW and on the edge of the northern banding. The only negating factor I see right now as forecast, is Erin may run into dry air in about 4-5 days. Other than that, she should have a somewhat favorable upper level wind pattern as seen in the shear forecast maps.
NHC FORECAST DISCUSSION INTENSITY FORECAST
FORECAST POSITIONS AND MAX WINDS INIT 15/1500Z 14.4N 26.5W 35 KT 40 MPH 12H 16/0000Z 15.0N 28.6W 40 KT 45 MPH 24H 16/1200Z 15.7N 31.2W 45 KT 50 MPH 36H 17/0000Z 16.7N 33.5W 45 KT 50 MPH 48H 17/1200Z 17.4N 35.8W 50 KT 60 MPH 72H 18/1200Z 18.0N 40.0W 50 KT 60 MPH 96H 19/1200Z 18.0N 44.5W 45 KT 50 MPH 120H 20/1200Z 18.0N 49.0W 35 KT 40 MPH
Based on analysis of the forecast steering maps, and various satellite loop imagery channels, I have to concur with the NHC forecast track on Erin, as ridging appears stronger and a little more expansive based on satellite loop imagery. As far as the dynamic model guidance, I prefer the OFCI / TV15 forecast track, which is the official track from the NHC.
ERIN 12Z DYNAMIC MODEL GUIDANCE
I will be monitoring Erin closely as she approaches the northern Lesser Antilles in 5 days, for any significant changes to the pattern that may allow for strengthening at that time, save any dry air intrusion, as upper level winds are forecast to be favorable at that time in the forecast period.
Have a blessed day!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST
MEMBER WEST CENTRAL FL AMS
CERTIFIED SKYWARN OFFICIAL STORM SPOTTER (advanced)