Good evening from the Forecast Center:
This is an update to the previous forecast discussion from this morning. INVEST 91L continues to show signs of some very slow organization this evening. Analysis of the 12Z GFS Wind Shear Forecast indicates upper level winds may remain favorable to slightly favorable for further development of this disturbance during the next 48 – 54 hours. Based on this, combined with the NHC update at 2:00 p.m. increasing the probability of development, INVEST 91L could very well become a sub-tropical or tropical depression over the next 72-96 hours, SHOULD conducive conditions pan out as forecast.
Based on the 18Z run of the ATCF Dynamic Model Guidance (early), which closely resembles the 12Z Dynamic Guidance (late), I agree with the track shown by the TVCN / TVCC.
Based on this current updated information, and the Intensity Forecast Models update (18Z), residents along the SC / NC coasts may wish to monitor this system closely for any significant changes to forecast parameters regarding possible development, and possibly minimal Tropical Storm conditions if development occurs.
Please note…the most accurate intensity models are in this following order: SHIP, DSHP, and LGEM
Good morning all!
The tropics have picked up slightly. I have been watching this for a couple days now, as most of the Global Models did catch this and hint at some type of development. This is the first chance however, that I have time to sit down and analyze the situation.
INVEST 91L was designated at 12Z yesterday morning, just off the SC / GA coast. Currently, the disturbance is pretty much quasi-stationary as steering currents are weak at the moment, and should remain as such during the next 30 – 36 hours. Thereafter, based on analysis of the current forecast steering layers maps, modeling is split on forecast track. This is expected during this early stage, as the modeling does not have a solid low level circulation to pick up on as far as initialization. Based on the forecast at this time, INVEST 91L should move either…toward the SSE, then loop toward land….or remain stationary, then be carried off toward the NE. Again, model guidance should improve over the next 24 hours as far as possible track guidance. The only guidance available at this time is from the 12Z Statistical models. The Dynamic models are the ones we use for track guidance. Based on the ATCF FTP data from 12Z, the following information was available on INVEST 91L:
MAX SUSTAINED WIND: 25 MPH
PRESSURE: 1016 MB / 30.00 IN.
INVEST 91L FLOATER SATELLITE LOOP IMAGERY
Based on analysis of vorticity maps, the system is currently very shallow, with the strongest vorticity showing up only from 925mb – 700mb. At the time the product was put out, the system was slightly tilted, however in the last couple of loops in satellite imagery, 91L since then appears to have become slightly better organized.
Based on my analysis of current and forecast wind shear products, and SST’s, I agree with the NHC TWO, in that INVEST 91L should continue with slow development over the next 96 – 120 hours, as upper level winds are currently favorable for continued slow development with an anticyclonic upper level flow over the area at the moment. Upper level winds are forecast to be favorable during the next 48 hours, and then becoming somewhat marginal as far as the flow pattern…however, shear values are forecast to remain at around only 10 – 15 knots over the next 96 hours. Based on this analysis, we could see 91L possibly become a sub-tropical depression near the end of the forecast period. In order to be classified tropical, it would have to become detached from the associated front.
Based on the early intensity scheme, I am with a blend of the SHIPS and LGEM models. This of course will change over the next few runs.
I will continue to monitor 91L over the next few days, and may have another update either sometime this evening, or late tomorrow afternoon.
Have a blessed weekend!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST / SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS
OFFICIAL SKYWARN SPOTTER (ADVANCED)