*******Note that forecasts and outlooks in this post are NOT the official forecast from the National Hurricane Center (NHC). They are my own detailed views on the Atlantic tropics based on current observations and latest computer model runs. As such do not make decisions based on my posts...consult news media...watches and warnings from your local weather office...and any evacuation orders issued by local governments to make the most informed and best decisions. Visit the NHC website hurricanes.gov (hurricanes dot gov) for the latest watches/warnings and official forecasts on active tropical cyclones.**********
...SATURDAY SEPTEMBER 4 2021 12:15 AM EDT...
See Larry section below for more info on the only currently active tropical cyclone in the Atlantic basin. See area of interest sections below for all areas being monitored for tropical cyclone formation in the Atlantic.
Elsewhere… satellite imagery shows a tropical wave of low pressure over Western Africa that has been generating western thunderstorm squalls that have reached the coast of Africa and far eastern Atlantic waters. However these squalls are not organized… and model support showing the wave developing after exiting Western Africa has reduced. Therefore the wave has not been added as an area of interest for development at this time.
The eastern divergence zone of an upper vortex currently northeast of the Bahamas has produced a persistent thunderstorm complex in the vicinity of 26N-57.5W. No models show development here… and any surface low pressure area that does form here will likely succumb to the dominating surface inflow and upper outflow of Hurricane Larry which is approaching this region.
HURRICANE LARRY (RECENTLY UPGRADED TO MAJOR HURRICANE LARRY)… Larry continues to gradually intensify and as of 5 PM EDT reached category 2 hurricane status as an eye became better defined in satellite pictures. When looking at colorized infrared pictures around and before that time… it had been apparent that thunderstorm activity was weaker on the north side of the hurricane… perhaps an indication of dry Saharan air affecting the hurricane. However recent colorized infrared satellite pictures show Larry having a more solid ring of thunderstorms around the eye… and as of 11 PM EDT is now a category 3 major hurricane with 115 mph max sustained winds. With these observations and current intensity being higher compared to my previous forecast… I have raised my updated short-term intensity forecast by moving Larry further up in the category 4 wind range by 24 hours. In addition to the improved core structure… Larry for the time being is aided by the low shear and upper outflow of the tropical Atlantic upper ridge… so short-term intensification to category 4 is on the table. I drop the intensity forecast down to category 3 by day 2 as Larry potentially sees some western outflow blockage while approaching the upper vorticity currently lingering in the central Atlantic. The latent heat release of Larry is Forecast in the GFS to dissipate this cool core upper vorticity by day 3… a bit sooner than shown in prior GFS runs. Therefore my intensity forecast is also raised for days 3 to 5… projecting that Larry could make a run for stronger category 4 status.
Regarding track… my short-term forecast points are nudged north from the current position of the hurricane. The current speed of Larry and near-term forecast track is faster than the typical 5W longitude per day of tropical systems in the low-latitudes for the next 24 hours. After that time the models show Larry slow down a bit as the west side of the Atlantic surface ridge weakens from the remnants of Ida. Also a more north track angle is expected as Larry will be strong/tall enough to be influenced by the lingering central Atlantic upper vorticity. Because the upper vorticity dissipates sooner in the modeling as noted in the prior paragraph… my longer term track forecast is nudged south. A turn to the north is still expected toward the late part of the 5-day forecast period while heading toward a large surface ridge weakness to be induced by a pair of frontal systems to eject from North America behind Ida’s remnants. The north turn will also be aided by the current upper vortex located northeast of the Bahamas. It should be noted the western convergence zone of the upper trough tied to the first of the ejecting frontal systems (the system currently over central Canada) will produce a passing surface ridge in the northwest Atlantic which could keep Larry’s track on a slight west lean in track by day 5. On the current forecast track… Larry will bring coastal sea swells to the northern Lesser Antilles and Bermuda by days 3 to 5. Interests in Bermuda should be aware the current forecast track brings Larry near Bermuda by day 5… and that any west shift in track could expose the island to tropical storm conditions under the west side of the hurricane.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0000Z Sep 4)… 100 mph maximum sustained wind hurricane centered at 15.4N-42.7W
IOH 24 Hr Forecast (0000Z Sep 5)… 140 mph maximum sustained wind major hurricane centered at 16.5N-48W
IOH 48 Hr Forecast (0000Z Sep 6)…120 mph maximum sustained wind major hurricane centered at 18.5N-52W
IOH 72 Hr Forecast (0000Z Sep 7)… 135 mph maximum sustained wind major hurricane centered northeast of the Lesser Antilles at 19.8N-57W
IOH 96 Hr Forecast (0000Z Sep 8)… 145 mph maximum sustained wind major hurricane centered at 23.5N-59W
IOH 120 Hr Forecast (0000Z Sep 9)… 145 mph maximum sustained wind major hurricane centered southeast of Bermuda at 29N-61W
AREA OF INTEREST #1… The tropical low pressure area that was over the Nicaragua/Honduras border yesterday has moved west-northwest into Belize and the Yucatan peninsula of Mexico. Although offshore northern thunderstorm bands developed this past afternoon over the western Caribbean waters… the activity has weakened and become disorganized as this system moves further into Belize and the Yucatan. The future evolution of this system lies with upper vorticity that has been deposited into the Gulf of Mexico by the upper trough associated with Ida’s remnants. The modeling shows the upper vorticity weakening to a small western Gulf vortex by 2+ days while this batch of cool core upper vorticity remains cut-off from high-latitude cold air. The GFS and now the ECMWF show this disturbance reform northward while transitioning into a system aided by the eastern divergence zone of the forecast upper vortex. By days 4 and 5 both models also show this system shift east-northeast toward the Florida panhandle in the flow ahead of the pair of frontal systems to cross North America in ex-Ida’s wake (the first system of the pair is already currently crossing central Canada). Although the more reliable GFS and ECMWF models have recently latched onto this system… I have not raised odds of development above 20% as this system remains weak and poorly organized for now. Odds are dropped to 0% by day 5 due to the inland location of my forecast track during that timeframe.
While it is concerning that this system by day 4 will be near southeast Louisiana where Hurricane Ida recovery efforts are ongoing… it appears this system has lower development potential than Ida did as it will have to negotiate Gulf of Mexico upper vorticity as discussed above… followed by possible westerly shear on the South side of the North American frontal systems’ upper troughs while nearing the US Gulf coast. Also the steering flow for now would suggest a track toward the northeast US Gulf coast… to the east of the Hurricane Ida impact region.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Sep 5)… 0% chance of tropical cyclone formation (just offshore of the western Yucatan peninsula near 19.5N-91W)
IOH 48 Hr Outlook (0000Z Sep 6)… 0% chance of tropical cyclone formation (southwestern Gulf of Mexico near 22N-92W)
IOH 72 Hr Outlook (0000Z Sep 7)… 10% chance of tropical cyclone formation (southwestern Gulf of Mexico near 24N-92W)
IOH 96 Hr Outlook (0000Z Sep 8)… 20% chance of tropical cyclone formation (offshore of southeast Louisiana near 27.8N-89.5W)
IOH 120 Hr Outlook (0000Z Sep 9)… 0% chance of tropical cyclone formation (southern Alabama/Georgia border at 31N-85W)
AREA OF INTEREST #2… Ida’s remnant low and it’s amplified supporting upper trough has driven a cold front into the west Atlantic.
Will watch to see if the tail end of the front evolves into a tropical disturbance offshore of Florida to be enhanced by divergence to develop on the east end of the current Gulf of Mexico upper vorticity recently left behind by the upper trough. The forecast track for this area of interest remains the same… showing whatever low pressure area that forms from the tail end of the front taking a slow anticyclonic Loop turn thru 48 hours while pushed around by the South side of the approaching eastern North America surface ridge. The slow motion is expected from the Atlantic surface ridge to the east which will counter the force from the approaching eastern North America surface ridge. By 3+ days… a turn to the northeast is expected in the flow ahead of the frontal system to approach from central Canada. The odds are lowered to 0% by day 3 due to westerly shear to be induced by the approach of the upper trough associated with the incoming frontal system from Central Canada. Also my peak odds of development have been lowered to 10% as no organized area of thunderstorms has developed along the tail end of the front thus far.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Sep 5)…0% chance of tropical cyclone formation (offshore of northeast Florida near 29.5N-78W)
IOH 48 Hr Outlook (0000Z Sep 6)… 10% chance of tropical cyclone formation (offshore of the southeastern US near 30.5N-78.5W)
IOH 72 Hr Outlook (0000Z Sep 7)… 0% chance of tropical cyclone formation (offshore of North Carolina near 33N-76.5W)
AREA OF INTEREST #3… The tropical wave of low pressure that recently passed over the southern Republic of Cabo Verde Islands has never redeveloped any thunderstorm activity… perhaps an effect of nearby dry Saharan air. The NHC has dropped this feature from their Outlook product… and likewise this is my final statement on this wave on this blog… especially as the current upper vorticity in the northeast Atlantic will shift southwest over top this wave and make upper level winds not conducive for development.
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z CMC Model Run...
**For Hurricane Larry… located at 27.5N-59.5W at 120 hours
**For area of interest #1…no development shown
**For area of interest #2… no development shown
**For area of interest #3… no development shown
1200Z ECMWF Model Run…
*For Hurricane Larry… located at 27N-58W at 120 hours
**For area of interest #1… evolves into broad western Gulf of Mexico tropical low by 120 hours… northeast part of the tropical low evolves into a compact circulation making landfall on the Florida panhandle at 144 hours
** For area of interest #2… no development shown
**For area of interest #3… no development shown
**Tropical wave forecast to emerge from Western Africa at 24 hours… evolves into a tropical low located just southeast of the Republic of Cabo Verde Islands at 48 hours… tropical low opens back to a wave passing 36W at 120 hours
1800Z GFS Model Run...
**For Hurricane Larry… located southeast of Bermuda at 28.5N-61.2W at 120 hours
**For area of interest #1… evolves into broad western Gulf of Mexico tropical low by 111 hours… northeast part of the tropical low evolves into a compact circulation just offshore of the Florida panhandle at 123 hours
**For area of interest #2… no development shown
**For area of interest #3… no development shown
1200Z NAVGEM Model Run...
**For Hurricane Larry… located at 23N-59.5W at 120 hours
**For area of interest #1… no development shown
** For area of interest #2… low pressure consolidates along the front near 32.5N-71W at 18 hours… approaching frontal low from central Canada absorbs this system while it is located near 41N-56.5W at 96 hours
**For area of interest #3… no development shown
**Tropical wave forecast to emerge from Western Africa by 24 hours… consolidates into broad tropical low near 10N-29W at 90 hours… broad tropical low intermittently loses and regains definition while moving slowly west and reaches 12N-37.5W at 168 hours.
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