*******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 17 2022 3:45 AM EDT...
Tropical Storm Fiona beginning to lash the northeastern Caribbean Islands with tropical storm conditions while putting up a fight and maintaining itself in a shear environment. See Fiona section below for more information. See area of interest #29 and #30 sections below for an update on the pair of tropical waves of low pressure located well east of Tropical Storm Fiona and in the tropical Atlantic. See area of interest #31 section below for information on a northwestern Atlantic frontal low being monitored by the NHC for signs of tropical development. Elsewhere... also noting an additional pair of tropical waves of low pressure over western and central Africa as follows:
(1) A tropical wave of low pressure over western Africa... in the vicinity of 10W longitude... has become less organized. There is a current lack of computer model support showing this wave developing as it later moves into the tropical Atlantic.
(2) A tropical wave of low pressure over central Africa... in the vicnity of 10E longitude... has also become less organized. However the current global model consensus suggests some development of this wave as it later moves into the eastern tropical Atlantic in about five days. This tropical wave could emerge as another area of interest in future updates if these trends continue.
New to this site this year... I will be sequentially numbering up areas of interest for possible Atlantic tropical development. In this scheme... will reset back to #1 at the start of next year (January 2023). The current areas of interest in this blog post are designated #29 to #31 as the other twenty-eight were mentioned in previous birdseye view posts. This scheme is to reduce confusion as Atlantic tropical activity increases during the peak of the hurricane season... when multiple simultaneous areas of interest begin and end which previously required shuffling around the area of interest numbers from update to update.
TROPICAL STORM FIONA...The center of circulation of the sixth tropical storm of the 2022 Atlantic Hurricane Season has recently crossed the northern Lesser Antilles and is now in the northeastern edge of the Caribbean Sea. The upper vorticity that was previously approaching Fiona from the northeast has consolidated into a distant upper vortex currently interacting with area of interest #29 and the global models have stopped suggesting that a lingering portion of this vorticity will be pushed around the western Atlantic upper ridge and chase Fiona. Despite this... Fiona remains sheared and this time by a string of upper vorticity that remains in the central Caribbean Sea. Before the center moved across the northern Lesser Antilles... the ongoing shear kept Fiona's thunderstorms east of its swirl center and the tropical storm weakened to 50 mph maximum sustained winds. While entering the northeastern edge of the Caribbean... Fiona has more recently put up a good fight against the shear while now firing bubbling thunderstorm bursts directly over the center. As of 11 PM EDT... aircraft reconnaissance confirmed Fiona has regained 60 mph maximum sustained winds.
The eastern divergence zone of a cut-off upper trough over the southeastern United States is currently supporting an offshore surface front and frontal low currently tagged area of interest #31 in this blog post... and will help materialize an inverted surface trough in the vicinity of the Florida peninsula over the next day or so. Models are in good agreement that Fiona in the next 48 hours will proceed westward and respond to the slight surface ridge weakness caused by area of interest #31 and inverted surface trough by having a slight north angle in the westward track. I forecast Fiona to also hold its current strength during the next 48 hours as the current levels of shear have been just right for Fiona to not strengthen and also to not weaken... with this shear level remaining as the shearing Caribbean upper vorticity remains. Between 48 and 72 hours the latest round of model runs are in remarkable agreement about an abrupt northwest turn that causes Fiona's center to thread the waters between Puerto Rico and the Dominican Republic... allowing Fiona at the last minute to avoid moving into the Dominican Republic/Haiti landmass. To make this turn... the models see the Caribbean upper vorticity and its shear weakening just in the nick of time... allowing Fiona to suddenly strengthen and become tall enough to make a more north turn while feeling the steering effects of what is left of the dissipating Caribbean upper vorticity. While it is inevitable that the Caribbean upper vorticity will weaken as it remains cut-off from high latitude cold air thanks to the warm western Atlantic upper ridge... there is no guarantee the upper vorticity weakens at the exact time needed to allow Fiona to strengthen and make its abrupt turn that allows it to just miss the Dominican Republic landmass. My previous forecast track is southwest of the latest model consensus... and so I have begun to shift my forecast track toward the new consensus which increases the land interaction with the Dominican Republic. My current forecast track thus represents the alternative should the Caribbean upper vorticity and its shear hang around just a little bit longer...causing Fiona to not turn as sharply north and instead move right into and then across the Dominican Republic. The land interaction with a large swath of the Dominican Republic is why in the updated forecast below I start weakening Fiona at 48 hours and barely keep Fiona as a tropical depression at 72 hours. If in fact this latest model consensus holds and observations in future updates support... I will have move the forecast track into the consensus and indeed show Fiona just missing the Dominican Republic in future updates.
For the 72+ hour timeframe... the models have also shifted in their handling of the current southeast US cut-off upper trough and how it interacts with another northern upper trough to slide east across the US/Canada border region. Previously the northern upper trough was shown to briefly merge with the southeastern US upper trough on the 20th and 21st of September... helping to expand the surface ridge weakness being generated by the southeastern US upper trough... with the weakness beginning to close on the 22nd as the northern upper trough moves away. Now the models see that the northern upper trough will be amplified enough to stay merged with the southeastern US upper trough through the 22nd... with the merged upper trough moving offshore while featuring a southwest-northeast tilt. This keeps the surface ridge weakness open such that even if Fiona becomes weak/shallow during a land interaction with the Dominican Republic that the surface flow would still be able to turn Fiona north. The latest model consensus shows that soon after Fiona just misses the Dominican Republic... it strengthens further into a hurricane in the absence of shear in the wake of the dissipating Caribbean upper vorticity. In turn the hurricane immediately curves more north in track while tall enough to feel the upper westerly flow ahead of the approaching merged upper trough. In my current forecast track where Fiona weakens to a shallow feature from land interaction with the Dominican Republic... I initially negate the steering effect of the increasing upper westerly flow ahead of the approaching merged upper trough and instead more gradually curve Fiona northward in the surface flow... as the surface ridge weakness induced by the merged upper trough gradually opens up. By 96 hours I show a re-strengthening Fiona taking advantage of lower shear in the absence of the dissipated Caribbean upper vorticity such that it becomes tall enough by 120 hours to sharply turn northeast once the approaching merged upper trough moves into Fiona with stronger upper southwesterly flow. While this stronger upper flow may begin to shear Fiona at 120+ hours... the northeast direction of travel somewhat aligned with the direction of the upper flow would help reduce the effect of shear. There is also a possibility of a zone of supportive upper divergence developing between the approaching upper trough and what would be left of the western Atlantic upper ridge... another thing that may help Fiona in the face of re-developing shear at 120+ hours. Thus I show slight strengthening from 96 to 120 hours... a balance between the negative effect of the re-developing shear and positive effect of possible upper divergence.
Regarding impact to land areas:
(1) Interests in the northern Lesser Antilles... Virgin Islands... and Puerto Rico should have finished preparing for Fiona by now. Tropical storm conditions (gusty winds... heavy rains with flash flooding potential... and coastal sea swells) are occurring in the northern Lesser Antilles... and will encompass the Virgin Islands and Puerto Rico by tonight.
(2) Interests in the eastern Dominican Republic should now be preparing for similar tropical storm conditions expected to arrive by Sunday. Finish preparations by tonight.
(3) If my current forecast holds.. or if the model consensus shifts back to a more west and less north track in the medium range... heavy rainfall with flash flooding potential will also be a concern for the western Dominican Republic and Haiti by Monday. Gusty winds and coastal sea swells here would be unlikely as Fiona would weaken from land interaction with the Dominican Republic and Haiti on a more west track.
(4) Interests in the Bahamas and eastern Cuba should remain aware of Fiona due to long-range uncertainty in the track and intensity of the storm. The potential for tropical storm impacts to eastern Cuba and western Bahamas has decreased... and has increased for the central and eastern Bahamas... per the latest model consensus. If the latest computer model consensus holds where Fiona just misses the Dominican Republic landmass and continues to strengthen... this opens the door for more damaging hurricane-force conditions in the central and/or eastern Bahamas by Tuesday or Wednesday.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0000Z Sep 17)...60 mph maximum sustained wind tropical storm centered just west of the northern Lesser Antilles at 16.6N-62.2W
IOH 24 Hr Forecast (0000Z Sep 18)...60 mph maximum sustained wind tropical storm centered just south of Puerto Rico at 17N-66W
IOH 48 Hr Forecast (0000Z Sep 19)...50 mph maximum sustained wind tropical storm centered on the south coast of the Dominican Republic at 18.5N-70W
IOH 72 Hr Forecast (0000Z Sep 20)...30 mph maximum sustained wind tropical depression centered between Haiti and the eastern Bahamas at 20.5N-73.5W
IOH 96 Hr Forecast (0000Z Sep 21)...50 mph maximum sustained wind tropical storm centered just south of the central Bahamas at 22.5N-76W
IOH 120 Hr Forecast (0000Z Sep 22)...60 mph maximum sustained wind tropical storm centered northeast of the central Bahamas at 25N-72.5W
AREA OF INTEREST #29...The tropical wave of low pressure located well east of Tropical Storm Fiona has developed a tropical low pressure spin at the north end of its axis. It is probable that upper divergence on the southeast side of the nearby cut-off upper vortex has helped to trigger the tropical low pressure spin. While transitioning into a feature supported by the divergent east side of the upper vortex... the tropical low is likely to turn north over the next 72 hours. I have lowered odds of tropical cyclone formation to 0% for the next 24 hours as the tropical low has not made further progress in developing. I follow with low 10% odds of tropical cyclone formation during the 48 to 72 hour timeframe as the modeling depicts an upper vortex elongated north-south... potentially resulting in an elongated upper divergence zone on the east side of the vortex that potentially elongates the tropical low itself such that the establishment of a tight center needed for tropical development becomes challenging.
By 96 hours... the major upper trough currently approaching from eastern Canada will have lodged a cell of western Atlantic upper ridging into the eastern Atlantic. A more focused area of upper divergence between the northeast corner of the upper vortex and northwest side of this eastern Atlantic upper ridge cell may allow for a more focused surface spin to develop within the tropical low pressure...and this is when I increase development odds to 20%. Once the major upper trough shifts northeastward and away into the northeast corner of the Atlantic at 120 hours... the eastern Atlantic upper ridge cell and remainder of the western Atlantic upper ridge have potential to bridge over this disturbance... providing a better upper outflow and lower shear environment needed for tropical development. This is when I raise odds of tropical cyclone formation further to 30%. An increasing turn to the west is depicted at 96 and 120 hours as this disturbance rounds the north side of the upper vortex and responds to a building surface ridge to the north to be supported by the western convergence zone of the departing major upper trough.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Sep 18)...0% chance of tropical cyclone formation (central Atlantic near 20.5N-45W)
IOH 48 Hr Outlook (0000Z Sep 19)...10% chance of tropical cyclone formation (central Atlantic near 23N-45W)
IOH 72 Hr Outlook (0000Z Sep 20)...10% chance of tropical cyclone formation (central Atlantic near 26.5N-45W)
IOH 96 Hr Outlook (0000Z Sep 21)...20% chance of tropical cyclone formation (central Atlantic near 27.8N-47W)
IOH 120 Hr Outlook (0000Z Sep 22)...30% chance of tropical cyclone formation (central Atalntic near 28.5N-51W)
AREA OF INTEREST #30...The tropical wave of low pressure currently southwest of the Republic of Cabo Verde Islands continues to produce a defined area of low clouds and thunderstorms. The wave has not become better organized while still lacking a defined center of rotation. My current best guess at an area of maximum spin... using satellite animation... is 10N-28.5W which is southwest of my previous forecast track... and so my updated one is adjusted accordingly. By the end of the 5-day forecast period... a more north angle in the westward track is possible due to a large scale western Atlantic surface ridge weakness currently anticipated from the combination of Tropical Storm Fiona and the eastern divergence zone of a southwest-northeast tilted upper trough to emerge from eastern North America (more information about this upper trough is in the Fiona section above). Regarding odds of tropical cyclone formation... I have lowered short-term odds as the tropical wave has not made progress in developing further. I have also lowered longer term odds of development to 10% as the global models still do not develop this tropical wave... and there is uncertainty as to what the upper vortex currently interacting with area of interest #29 will do. The current model consensus has a stronger version of Fiona located further east in the longer range... allowing its upper outflow to push the upper vortex southward into this tropical wave where it would arrest the wave's development by increasing wind shear and suppressing upper outflow. However if Fiona tracks more west and is weaker as I currently forecast... its upper outflow would not be able to push the upper vortex as far south... perhaps allowing the tropical wave to still have an area of upper outflow just south of the vortex. This alternative scenario is why I do not drop development odds back to 0% in the long range in this update.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Sep 18)...0% chance of tropical cyclone formation (eastern tropical Atlantic near 10.5N-33.5W)
IOH 48 Hr Outlook (0000Z Sep 19)...0% chance of tropical cyclone formation (eastern tropical Atlantic near 10.5N-38.5W)
IOH 72 Hr Outlook (0000Z Sep 20)...10% chance of tropical cyclone formation (central tropical Atlantic near 11N-43.5W)
IOH 96 Hr Outlook (0000Z Sep 21)...10% chance of tropical cyclone formation (central tropical Atlantic near 11.5N-48.5W)
IOH 120 Hr Outlook (0000Z Sep 22)...10% chance of tropical cyclone formation (central tropical Atlantic near 12.5N-53W)
AREA OF INTEREST #31...A frontal low pressure that formed offshore of the southeastern United States yesterday... supported by the eastern divergence zone of the cut-off upper trough currently over the southeastern United States... has spent Friday and the early morning hours of today accelerating eastward. This is due to the eastward ejection of a fragment of the cut-off upper trough that has been dislodged by the current major eastern Canada upper trough... with the frontal low transitioning into a feature supported by the divergence zone of this eastward-accelerating fragment. Despite the frontal low being underneath a solid area of upper westerly shearing winds... the National Hurricane Center introduced this feature into its tropical weather outlook with 10% odds of tropical cyclone formation. I suppose this is due to the eastward acceleration of the frontal low which helps it keep up with the upper westerly wind speed... reducing some of the effect of the shear. For example as of this writing there is a thunderstorm flare just east of the frontal low's center instead of being well-removed from the center. There is potential for the frontal low to slow down its eastward speed in the next 24 hours while becoming jammed between the Atlantic surface ridge to the east-southeast and approaching surface ridge to the northwest which will only make the westerly shear worse. Thus I assign 0% odds of tropical cyclone formation... and this is my planned only and final statement on this area of interest on this blog unless it continues to be mentioned in the NHC tropical weather outlook.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Sep 18)...0% chance of tropical cyclone formation (east-northeast of Bermuda near 34N-60W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z (Sep 16) CMC Model Run...
**For Tropical Storm Fiona... while gradually strengthening moves across the northern Lesser Antilles and then just south of the Virgin Islands and over the southwest coast of Puerto Rico from 12 to 42 hours... moves northwest across the north coast of the Dominican Republic through 72 hours... moves northwest into the eastern Bahamas at 90 hours... slides across the central Bahamas at 108 to 120 hours at hurricane strength.
**For area of interest #29... no development shown
**For area of interest #30... no development shown
**For area of interest #31... frontal low passes just north of Bermuda at 24 hours... frontal low dissipates northeast of Bermuda near 34N-61W at 102 hours
**Tropical wave emerges from west coast of Africa at 132 hours... organizes into a broad tropical low midway between the west coast of Africa and Republic of Cabo Verde Islands through 156 hours... tropical low located just northeast of the Republic of Cabo Verde Islands at 168 hours.
1200Z (Sep 16) ECMWF Model Run...
**For Tropical Storm Fiona... moves across the northern Lesser Antilles and then just south of the Virgin Islands and over the southwest coast of Puerto Rico from 12 to 48 hours... while strengthening moves northwest across the north coast of the Dominican Republic through 96 hours... turns increasingly north into the eastern Bahamas while becoming a compact hurricane through 144 hours.
**For area of interest #29... no development shown
**For area of interest #30... no development shown
**For area of interest #31... frontal low passes just northeast of Bermuda at 24 hours... dissipates in the open central Atlantic near 32.5N-55W just after 96 hours
**Tropical wave emerges from west coast of Africa at 120 hours... organizes into a broad tropical low midway between the west coast of Africa and Republic of Cabo Verde Islands through 144 hours... becomes a tropical cyclone while passing over the northern Republic of Cabo Verde Islands through 168 hours.
1800Z (Sep 16) GFS Model Run...
**For Tropical Storm Fiona... while gradually strengthening moves across the northern Lesser Antilles and then just south of the Virgin Islands and over the southwest coast of Puerto Rico from 9 to 42 hours... additional strengthening forecast while moving northwest across the north coast of the Dominican Republic through 63 hours... turns increasingly north and becomes a compact hurricane at 21N-69W at 69 hours... moves north and reaches 26N-69.5W at 120 hours while growing in size and potentially becoming an intense hurricane.
**For area of interest #29... north side of tropical wave fractures as a northward-moving surface trough which strengthens into a surface low near 25.5N-45W at 60 hours... surface low turns more west and reaches 28.5N-52W at 120 hours.
**For area of interest #30... no development shown
**For area of interest #31... frontal low passes just north of Bermuda at 18 hours... afterwards meanders in a clockwise loop turn just east of Bermuda and then swings north... frontal low dissipates northeast of Bermuda near 35N-62.5W at 105 hours.
**Tropical wave emerges from west coast of Africa at 132 hours... organizes into a broad tropical low midway between the west coast of Africa and Republic of Cabo Verde Islands through 153 hours... tropical low located just east of the Republic of Cabo Verde Islands at 168 hours.
1800Z (Sep 16) NAVGEM Model Run...
**For Tropical Storm Fiona... while gradually strengthening moves across the northern Lesser Antilles and then just south of the Virgin Islands and over the southwest coast of Puerto Rico from 6 to 36 hours... additional strengthening forecast while moving northwest across the north coast of the Dominican Republic through 66 hours... moves northwest into the eastern Bahamas at 84 hours while reaching hurricane strength... turns increasingly north and reaches 25.5N-72.5W through 120 hours as a potentially large and intense hurricane.
**For area of interest #29... no development shown
**For area of interest #30... no development shown
**For area of interest #31... no development shown