*******Note that forecast 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.**********
...MONDAY SEPTEMBER 11 2023 1:45 PM EDT...
See Hurricane Lee and Tropical Storm Margot sections below for the two currently active tropical cyclones in the Atlantic basin. The largest concern in the Atlantic basin for land areas is Hurricane Lee which is expected to remain strong while curving northward between Bermuda... the United States east coast... and the Bahamas over the course of the next five days. After potentially passing near Bermuda by day 3... Lee is likely to strike the eastern part of the northeastern United States and/or Nova Scotia after day 5 as an enlarging and still strong hurricane. See Lee section below for more information on expected impacts to land areas.
In addition... a pair of tropical waves of low pressure well to the southeast of Tropical Storm Margot have become closely-spaced and are beginning to interact with each other. One of the waves is now expected to absorb the other and potentially develop into a tropical cyclone in the central tropcial Atlantic over the next five days... see area of interest #34 and #35 sections below for details.
Elsewhere... METEOSAT satellite imagery shows a well-defined tropical wave of low pressure with strong thunderstorms over central Africa (https://www.goes.noaa.gov/FULLDISK/GMIR.JPG). This tropical wave will emerge from the west coast of Africa and into the eastern tropical Atlantic in about five days. It is not yet clear if upper winds in the eastern tropical Atlantic will be favorable or not for development as a high-latitude upper trough to pass north of Margot will be diving southeastward toward the eastern tropical Altantic under the influence of a warm core upper ridge to be bolstered by the warm sector of Lee... if this upper trough digs far south enough it may suppress the outflow of tropical upper ridging in the eastern tropical Atlantic and prevent the development of this wave. Therefore there are no additional areas of interest for tropical development in the Atlantic basin for the next five days.
MAJOR HURRICANE LEE... Satellite image of Hurricane Lee at 0130Z earlier today while reaching a peak category 3 strength with 120 mph maximum sustained winds while featuring a well-defined eye:
Lee... now located north of the northern Lesser Antilles and Virgin Islands... spent Sunday recovering from Saturday night's eye wall replacement cycle... gradually regaining a well-defined eye on satellite pictures and re-strengthening to a category 3 peak with 120 mph maximum sustained winds. Recent colorized infrared satellite pictures shows the hurricane has lost its well-defined eye perhaps as another eye wall replacement cycle will begin shortly... however aircraft recon through 11 AM EDT indicates for now that Lee is maintaining 120 mph maximum sustained winds. The hurricane is continuing northwest... a combination of the Atlantic surface ridge and dragging upper winds imparted by the decaying Caribbean upper vorticity to the southwest (the upper vorticity continues to decay while isolated from high-latitude cold air). The hurricane is further east than I previously anticipated it would be for the current timeframe (at the longitudes of the Virgin Islands instead of Puerto Rico)... perhaps as the decay rate of the Caribbean upper vorticity and its dragging upper winds has continued to be slower than previously thought. Therefore for the northward turn of the hurricane I have shifted my forecast track eastward and close to Bermuda. In general the northward turn is expected as what are currently upper troughs over the eastern US and central Canada are forecast to push the current eastern US frontal system into the western Atlantic... with the surface front helping to create a surface ridge weakness that helps the northward turn. Also the upper southerly flow ahead of the upper troughs will help the turn. Noting there remains notable north-south spread in the 5-day position of Lee as the CMC... NAVGEM... and ECMWF have a slower north turn and the GFS remains faster. My updated forecast track is therefore a little slower than what the 0600Z GFS showed. Also noting that by day 5 Lee has potential to hook more westward toward the northeastern United States coastline and Nova Scotia as the northwest side of the hurricane pulls down cold air associated with the amplified upper troughs southward... potentially creating a cold core upper vortex just west of Lee whose northeast side bends the track of the hurricane.
For intensity... I assume that Lee will weaken back down to a strong category 2 later today due to the degraded appearance of the hurricane... followed by re-development into a category 3 by 24 hours as the hurricane re-develops a healthy inner core and eye. By 48 hours I forecast the organized inner core and eye to hold as the westerly shear from the approaching upper troughs may not be too bad due to the amplified nature of the troughs... therefore I project category 4 status by then. As the upper troughs near and the shear potentially worsens... I then show weakening after 48 hours... in particular in between 72 and 96 hours as Lee nears the cool sea surface temperature wake caused by previous Hurricanes Idalia and Franklin. I slow the weakening rate between 96 and 120 hours as the tremendous eastern divergence zone of the potential forming upper vortex to the west aids Lee. The size of the upper divergence zone will also help grow the size of the weakening hurricane.
Regarding impact to land areas:
(1) Expect wide-reaching surf from this powerful hurricane to reach the northern Lesser Antilles... Virgin Islands... Puerto Rico... the north shores of Haiti and the Dominican Republic... the Bahamas... Bermuda... and the mid-Atlantic United States coast over the three days. Coastal surf will then increase across the coastal northeastern United States and Atlantic Canada (Nova Scotia and Newfoundland) by later in the week.
(2) Interests in Bermuda may see damaging tropical storm to hurricane force conditions (winds and more severe coastal surf) arriving by late Thursday and into early Friday... and may have to spend tomorrow and Wednesday preparing for Lee. Interests here should continue to closely monitor the progress of Lee and begin to prepare as soon as tropical storm or hurricane watches or warnings become raised.
(3) Interests across Nova Scotia and the northeastern United States to the east of New York should continue to monitor the progress of Lee as more direct impacts such as life-threatening coastal surf and damaging winds could affect parts of this region just after day 5. Even though Lee will be gradually weakening during its approach... damaging winds could affect a large area and life-threatening coastal surf will become a concern due to the expected growing size of the storm. Flash flooding heavy rainfall will be another hazard to contend with.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Sep 11)... 120 mph maximum sustained wind major hurricane centered in the western Atlantic at 23.1N-62.6W
IOH 24 Hr Forecast (1200Z Sep 12)... 115 mph maximum sustained wind major hurricane centered in the western Atlantic at 25N-65W
IOH 48 Hr Forecast (1200Z Sep 13)... 130 mph maximum sustained wind major hurricane centered south-southwest of Bermuda at 26.5N-65.5W
IOH 72 Hr Forecast (1200Z Sep 14)... 125 mph maximum sustained wind major hurricane centered south-southwest of Bermuda at 28.5N-65.5W
IOH 96 Hr Forecast (1200Z Sep 15)... 110 mph maximum sustained wind hurricane centered just southwest of Bermuda at 32N-65.5W
IOH 120 Hr Forecast (1200Z Sep 16)... 100 mph maximum sustained wind hurricane centered offshore of the northeastern United States at 38N-67.5W
******National Hurricane Center (hurricanes.gov) official forecast as of 11 AM EDT***************************
Peak Strength (1200Z Sep 12)... 130 mph maximum sustained wind major hurricane centered in the western Atlantic at 24.4N-65.5W
5-day Position (1200Z Sep 16)... 80 mph maximum sustained wind hurricane centered offshore of the northeastern United States at 38.9N-67.1W
TROPICAL STORM MARGOT... Margot as expected has made its northward turn into the open central Atlantic along 40W longitude while coming under the influence of upper southerly flow on the east side of the central Atlantic upper trough. The upper trough has materialized from the merger of a northwest Atlantic upper trough fragment and quasi-stationary central Atlantic upper vortex... and the eastern divergence zone of the upper trough fragment has brought in a surface trough to the north that is also helping to attract Margot northward at the surface/low-level layer of the atmosphere. The southerly shear that was affecting Margot has notably reduced as the tropical storm's current northward track is more in alignment with the upper southerly flow and as the latent heat release of the tropical storm's thunderstorms is helping to weaken the upper trough. Noting my current track forecast is nudged southward over the previous due to Margot's current position relative to the prior forecast. A westward bend in Margot’s track remains likely by 48 and 72 hours as a high-latitude upper trough currently over the northeast coast of Canada... originating as a northeast fracture of the current central Canada trough... will pass north of Margot and moves the surface trough northeast and away from Margot... with the western convergence zone of the high-latitude upper trough then re-building the Atlantic surface ridge due north of Margot. The steering pictures gets complicated around 72 hours as northwesterly flow on the southwest side of the high-latitude upper trough tries to drag Margot eastward while the recovered Atlantic surface ridge tries to do the opposite. By 120 hours conflicting steering is then continued as a warm core upper ridge to the northwest to be bolstered by the warm southerly flow on Lee's east side conflicts with warm core tropical upper ridging to the south. Not suprisingly the different global models each handle Margot a little differently... my solution for now is to hold Margot quasi-stationary from 72 to 120 hours.
Because Margot is initially stronger than my previous forecast and satellite pictures shows a healthy core with a banding type eye on colorized infrared and true-color visible satellite channels... I have notably increased my intensity forecast. Another boon to Margot's future intensity is the model fields now show the central Atlantic upper trough weakening to a more circular upper vortex to the southwest... reducing the probability of westerly shear at 48 hours. However I do not quiet show a major hurricane (115+ mph... or category 3+ max winds) for this timeframe as the nearby upper vortex may still obstruct the southwestern outflow of Margot. For 72 hours I show weakening back into a category 1 hurricane as shearing upper northwesterly flow from the southwest side of the passing high-latitude upper trough overspreads Margot. Between 72 and 96 hours there is a possiblity of Margot's northwest quadrant pulling down high-latitude cold air enough to make a shear-reducing local upper trough... and its also possible this doesn't happen... so I simply keep the intensity at an equilibrium during this timeframe. By 120 hours is is more likely that any local upper troughing in Margot's environment becomes directly stacked over the storm in between the aforementioned northwest Atlantic and tropical latitude upper ridges... with suppressing convergence directly below the troughing negatively affecting Margot. Thus I show weakening back to a tropical storm for the end of the 5-day forecast period.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Sep 11)... 70 mph maximum sustained wind tropical storm centered in the central Atlantic at 26.1N-40W
IOH 24 Hr Forecast (1200Z Sep 12)... 90 mph maximum sustained wind hurricane centered in the central Atlantic at 30N-40W
IOH 48 Hr Forecast (1200Z Sep 13)... 110 mph maximum sustained wind hurricane centered in the central Atlantic at 33N-41W
IOH 72 Hr Forecast (1200Z Sep 14)... 85 mph maximum sustained wind hurricane centered in the central Atlantic at 35N-43W
IOH 96 Hr Forecast (1200Z Sep 15)... 85 mph maximum sustained wind hurricane centered in the central Atlantic at 35N-43W
IOH 120 Hr Forecast (1200Z Sep 16)... 70 mph maximum sustained wind tropical storm centered in the central Atlantic at 35N-43W
******National Hurricane Center (hurricanes.gov) official forecast as of 11 AM EDT***************************
Peak Strength (0000Z Sep 13)... 90 mph maximum sustained wind hurricane centered in the central Atlantic at 31.9N-40.5W
5-day Position (1800Z Sep 14)... 65 mph maximum sustained wind tropical storm centered in the central Atlantic at 37N-41W
AREA OF INTEREST #34... The eastern Atlantic tropical wave of low pressure with ongoing compact area of rotating thunderstorms has arrived to 12.5N-30.5W as of 1200Z earlier this morning. This is notably southeast of my previous forecast as this system has not been able to run northwestward toward Margot's surface ridge weakness while being captured by another adjacent tropical wave to the east tagged as area of interest (AOI) #35 in this update. It is impossible for two nearby tropical systems to develop... usually the stronger of the two absorbs the weaker one and goes on to develop. As such... global models are split on whether this wave or AOI #35 goes on to dominate the region and develop further. Because this wave appears to be the better organized of the two in the most recent satellite pictures... in this update cycle I am providing this wave with higher odds of development than AOI #35. However I am keeping peak odds of development of this wave capped at 50% as it may struggle to develop within the next five days while becoming excessively broad without a well-defined center and concentrated thunderstorms as it potentially absorbs AOI #35... and also not all the global models agree that this wave will be the dominant feature in the region. The updated forecast track strategy is for the next 72 hours to keep this system moving slowly west while it continues to be dragged by AOI #35... followed by a still slow track with northward angle by 96 and 120 hours as this system reaches the southwest part of the Atlantic surface ridge which will be weakened by the presence of Lee and Margot. Unlike the previous update... I keep development odds at 50% thru day 5 instead of lowering the long term odds as the updated forecast track keeps this system away from shearing southerly winds associated with the central Atlantic upper trough interacting with Margot.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Sep 12)... 50% chance of tropical cyclone formation (eastern tropical Atlantic near 12.5N-33.5W)
IOH 48 Hr Outlook (1200Z Sep 13)... 50% chance of tropical cyclone formation (eastern tropical Atlantic near 12.5N-36.5W)
IOH 72 Hr Outlook (1200Z Sep 14)... 50% chance of tropical cyclone formation (eastern tropical Atlantic near 12.5N-39W)
IOH 96 Hr Outlook (1200Z Sep 15)... 50% chance of tropical cyclone formation (central tropical Atlantic near 13.5N-42.5W)
IOH 120 Hr Outlook (1200Z Sep 16)... 50% chance of tropical cyclone formation (central tropical Atlantic near 14.5N-46W)
******National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT***************************
Formation chance through 48 hours... 10%
Formation chance through 7 days... 10%
AREA OF INTEREST #35... The broad tropical wave of low pressure that was over western Africa spent Sunday moving into offshore waters to the southeast of the Republic of Cabo Verde Islands. For a time the wave appeared to be becoming more consolidated and better organized... however as of today the shower and thunderstorm activity of the wave is less organized. For reasons detailed in the above AOI #34 section I am keeping the development odds of this wave below the wave associated with AOI #34... however I have raised my peak odds of development to 40% in this update as some of the global models now prefer to develop this wave even though it is currently less organized than AOI #34. Forecast track strategy is to initially move this wave steadily westward as it potentially absorbs AOI #34... followed by an increasing northward angle in the track by day 5 as it reaches the southwest part of the Atlantic surface ridge which will be weakened by the presence of Margot and Lee. Noting that after day 5 the track could slow down its forward speed as it moves farther into the weaker part of the surface ridge. On a final note... the shower and thunderstorm activity of this wave is now passing south of the Republic of Cabo Verde Islands... therefore notable impacts to the islands from this wave are no longer anticipated.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Sep 12)... 0% chance of tropical cyclone formation (south-southwest of the Republic of Cabo Verde Islands near 12N-26W)
IOH 48 Hr Outlook (1200Z Sep 13)... 0% chance of tropical cyclone formation (eastern tropical Atlantic near 12.5N-31W)
IOH 72 Hr Outlook (1200Z Sep 14)... 10% chance of tropical cyclone formation (eastern tropical Atlantic near 13N-35W)
IOH 96 Hr Outlook (1200Z Sep 15)... 25% chance of tropical cyclone formation (eastern tropical Atlantic near 14N-39.5W)
IOH 120 Hr Outlook (1200Z Sep 16)... 40% chance of tropical cyclone formation (central tropical Atlantic near 15N-44W)
******National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT***************************
Formation chance through 48 hours... 0%
Formation chance through 7 days... 60%
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields(http://moe.met.fsu.edu/tcgengifs/).
0000Z (Sep 11) CMC Model Run...
**For Major Hurricane Lee... passes just west of Bermuda at 102 hours and located offshore of the northeastern US and Atlantic Canada while centered at 36N-66W at 120 hours
**For Tropical Storm Margot... reaches 36.5N-40W as a hurricane by 120 hours
**For Area of Interest #34... intially stationary while merging with AOI #35 and then begins to move west... tropical cyclone formation suggested near 13.5N-37.5W at 78 hours... reaches 17N-42.5W at 120 hours as a hurricane
**For Area of Interest #35... No development shown
**Tropical wave emerges from west coast of Africa at 108 hours... gradually organizes into a tropical low southeast of the Republic of Cabo Verde Islands through 168 hours
0000Z (Sep 11) ECMWF Model Run...
**For Major Hurricane Lee... passes just west of Bermuda at 108 hours and located northwest of Bermuda at 120 hours while centered near 34N-67W
**For Tropical Storm Margot... reaches 37N-40W as a hurricane by 120 hours
**For Area of Interest #34... develops into a broad tropical storm centered near 19N-58W at 144 hours
**For Area of Interest #35... no development shown
0600Z (Sep 11) GFS Model Run...
**For Major Hurricane Lee... passes just west of Bermuda at 93 hours and located just offshore of the northeastern United States at 120 hours while centered near 40N-67.5W
**For Tropical Storm Margot... reaches 37N-43W as a hurricane by 120 hours
**For Area of Interest #35... tropical cyclone formation suggested near 15.5N-40.2W at 105 hours... reaches 15.5N-44W at 120 hours as a strengthening tropical storm
0600Z (Sep 11) NAVGEM Model Run...
**For Major Hurricane Lee... passes just west of Bermuda at 108 hours and located midway between Bermuda and Massachusetts at 120 hours while centered near 37N-66.5W
**For Tropical Storm Margot... reaches 36N-34.5W at 120 hours as a strong hurricane
**For Area of Interest #34... no development shown while AOI #35 to the east becomes the dominant system
**For Area of Interest #35... reaches 14N-45W as a broad tropical low by 120 hours.
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