*******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.**********
...WEDNESDAY SEPTEMBER 21 2022 4:39 AM EDT...
Fiona pulling northward away from the easternmost Bahamas while strengthening further into a category 4 hurricane. See Fiona section below for more information the hurricane... including expected impacts to the mid-Atlantic and northeastern US coast... Atlantic Canada region... and Bermuda.
The surface low pressure area in the central Atlantic became Tropical Storm Gaston on Tuesday as outlined in special update #106A available on the home page of this site. See Gaston section below for more information on the new tropical storm.
Also monitoring three other areas of interest in the Atlantic tropics as follows:
(1) See area of interest #30 section below for information on a vigorous tropical wave moving toward northeastern Venezuela... Trinidad and Tobago... and the southern Lesser Antilles. There is an high risk this wave develops into a tropical cyclone that moves across the Caribbean Sea in the long range.
(2) See area of interest #32 section below for a tropical wave of low pressure that may develop midway between the west coast of Africa and Republic of Cabo Verde Islands in 72+ hours.
(3) See area of interest #33 section below for a tropical low pressure area west-southwest of the Republic of Cabo Verde Islands showing signs of organization.
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... #30... and #32 as the other numbers were used 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.
MAJOR HURRICANE FIONA... As expected... the core of Major Hurricane Fiona moved northward across the easternmost Bahamas (Turks and Caicos region) on Tuesday morning... and tonight the circulation of the hurricane is now clearing northward and away from the Bahamas under the steering southerly flow out ahead of a cut-off upper trough over the southeastern United States that has slid closer to Fiona while dragged by a northern upper trough that moved across the northeastern US. While moving across the easternmost Bahamas... Fiona did not reach its maximum potential intensity while its original small eye collapsed and became replaced by a new larger one... a classic eye wall replacement cycle. However the hurricane was still dangerous and impactful while a category 3 with 115 mph maximum sustained winds. The larger eye and core of Fiona has merged with the outer thunderstorm bands east of the center... giving the hurricane a more solid and formidable appearance. Aircraft recon confirmed tonight the more formidable looking hurricane has strengthened further to 125 mph maximum sustained winds. My updated forecast track is nudged north and west in the short-term due to Fiona's current position relative to the previous forecast. Fiona has another 24 hours of basically a due north track... after which time the track is expected to buckle more eastward once the cut-off upper trough from the southeastern US gets pushed even closer to Fiona by a second and more substantial northern upper trough to approach from central and eastern Canada. After 48 hours... the track is expected to bend more north and less east as Fiona gets funneled into the southerly flow out ahead of the amplified Canadian upper trough... sending it right into the sprawling divergence maximum on the trough's east side. The tremendous upper divergence will allow Fiona to grow into a large and powerful non-tropical remnant frontal cyclone once over cooler water... and the west side of the remnant cyclone will pull cold air associated with the trough southward and cause it to amplify further into an upper vortex. In turn this would mean the remnant cyclone between 72 and 96 hours swings northwest in track... right into Atlantic Canada... while whirling into the center of the forming upper vortex. Because of the initial west adjustment in the track... Fiona will be closer to the incoming Canadian upper trough which will allow its west side to more quickly pull the trough's cold air southward to a more southern location... thus the forming upper vortex could very well be at a more southern location. This explains my 96 hour forecast point being both a south and west adjustment relative to my previous forecast.
Regarding forecast intensity... shear over the hurricane should not be too bad for another 12 hours as the southeast US cut-off upper trough is taking its time in approaching Fiona and it would not surprise me if Fiona strengthens a little further assuming that it does not undergo another eye wall replacement cycle. My intensity at 24 hours is the same as the current intensity as the upper southwesterly flow (blocking the western outflow of the hurricane and perhaps lightly shearing it) could increase between 12 and 24 hours with the nearing of the southeast US cut-off upper trough... and so I assume that whatever peak intensity Fiona obtains in the next 12 hours will come back down to basically where Fiona's strength currently is. Shear being induced by the upper southwesterly flow could be mitigated as Fiona eventually accelerates northeast in the direction of the upper flow between 24 and 48 hours which is why I depict a slow weakening rate. At 48+ hours the tremendous eastern divergence zone of the incoming Canadian upper trough should also keep the weakening rate slow as the hurricane moves over lower sea surface temps and transitions to a ferocious non-tropical frontal cyclone.
Regarding impact to land areas:
(1) Coastal surf affecting the north coasts of the Dominican Republic and Haiti... northeast coast of Cuba... and the Bahamas should gradually wind down as Fiona pulls northward and away.
(2) The west shift in the long range track is enough for Fiona to bring more pronounced coastal swells and rip currents to the United States mid-Atlantic and northeast coastline. The west side of the ferocious remnant frontal cyclone could bring gusty winds to Maine this weekend.
(3) Expecting tropical storm conditions (heavy rainfall... coastal surf... and tropical storm winds with some damage potential) across Bermuda by Friday. I recommend preparations for such conditions be completed by midday Thursday.
(4) Fiona is expected to transition to a ferocious and potentially historic non-tropical frontal cyclone that pivots north across Atlantic Canada this weekend. Damaging hurricane force winds are becoming increasingly likely across eastern Nova Scotia... Prince Edward Island... western Newfoundland and eastern Quebec. Gale force winds with some damage potential are becoming increasingly likely across New Brunswick... western Nova Scotia... eastern Newfoundland... and Labrador. Across all of these areas... expect immense coastal surf with storm surges due to the forecast large size and strength of Fiona's remnant cyclone. Heavy rainfall with flash flooding potential is another hazard to consider. I recommend preparations in the region should start tomorrow evening if the current forecast holds.
Update as of 2 AM EDT... aircraft reconnaissance data has been showing Fiona's central pressure dropping steadily over the last several hours to the low 940s of mb. The surface wind speed has finally caught up to the dropping pressure... and now Fiona is a category 4 hurricane with 130 mph maximum sustained winds. Making no change to the intensity forecast below... as the above intensity forecast discussion mentions Fiona reaching a peak strength in the next 12 hours followed by possible weakening after that time.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0000Z Sep 21)...125 mph maximum sustained wind major hurricane centered north of the easternmost Bahamas at 23.2N-71.8W
IOH 24 Hr Forecast (0000Z Sep 22)...125 mph maximum sustained wind major hurricane centered at 26N-71W
IOH 48 Hr Forecast (0000Z Sep 23)...115 mph maximum sustained wind major hurricane centered west-southwest of Bermuda at 31N-69W
IOH 72 Hr Forecast (0000Z Sep 24)...100 mph maximum sustained wind hurricane centered at 40.5N-60.5W
IOH 96 Hr Forecast (0000Z Sep 25)...Hurricane-force remnant frontal cyclone centered in the western Gulf of St. Lawrence at 47.5N-62.5W
TROPICAL STORM GASTON...Special update #106A available on the home page of this site chronicles the transition of the surface low pressure spin in the open central Atlantic into Tropical Storm Gaston as of Tuesday. Going forward... the surface and upper layers of the atmosphere will provide conflicting steering directions. At the surface a ridge is expected to build to the north of Gaston which will attempt to induce a westward push... with the ridge itself supported by the western convergence zone of the upper trough currently pivoting eastward across the north Atlantic. In the upper layers... increasing upper westerly flow as the shortwave upper trough currently just west of Gaston cuts across the top of the storm will bend the track of Gaston eastward the longer it stays strong/tall enough to couple to the upper flow. My intensity forecast is not quiet as high as the NHC's as of this writing as this system will reach water temps below 26 deg C at 12+ hours. I currently forecast Gaston will weaken to a remnant low over the cooler waters by 48 hours. I expect the initial weakening to cause Gaston to become shallower... hence slowing down its eastward-bending track while decoupling from the upper westerlies and feeling more steering influence from the building northern surface ridge. The slow down would then mean the circulation falls behind the upper westerly wind speed... thus exacerbating wind shear which would induce further weakening. Because my intensity forecast is lower than the NHC... I do not bring this system as far east nor as close to the Azores. After this system becomes a shallow remnant low... the southwest side of the northern surface ridge should take over and reverse the track westward and then northwestward until the remnant low dissipates.
Should the remnant low take some time to spin down... it could bring coastal sea swells to the western Azores by Thursday.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0000Z Sep 21)...50 mph maximum sustained wind tropical storm centered at 36.2N-43.6W
IOH 24 Hr Forecast (0000Z Sep 22)...45 mph maximum sustained wind tropical storm transitioning into a remnant low at 39N-40.1W
IOH 48 Hr Forecast (0000Z Sep 23)...Remnant low centered west of the Azores at 39N-35W
AREA OF INTEREST #30...The central Atlantic tropical wave of low pressure bearing down on northeastern Venezuela... Trinidad and Tobago... and southern Lesser Antilles has seen its shower and thunderstorm activity suppressed to the south and disorganized by upper northerly flow being generated by the west side of an upper vortex in the region. However below the scattered thunderstorm cloud tops... low clouds suggest an area of rotation increasing with the tropical wave. And most recently the thunderstorm tops are beginning to form banding features that define the south side of the area of rotation. The area of rotation suggests a surface low pressure swirl is likely forming along the tropical wave axis with the support of split flow upper divergence between the southwest side of the upper vortex and southeast side of the upper ridge axis that lies ahead in the northern Caribbean Sea. There is some speculation that this split flow upper divergence could ramp up this system quickly in the short-term... and so I continue to set short-term odds of tropical cyclone formation at 15%.
Regarding the forecast track... the westward track is expected to bend more north over the next 72 hours toward the surface ridge weakness being induced by Hurricane Fiona. As the weakness closes by 96 hours with Fiona pulling northward and away... the forecast track bends back more westward. In the long range... the current upper vortex moving into the northwest US and a major upper trough that will soon slide eastward across the northeastern Pacific will merge... with the eastern divergence zone of the potent upper trough creating another surface ridge weakness over the eastern US by 120 hours. By 120 hours a north angle in track toward this weakness is shown. My peak 5-day odds of tropical cyclone formation are set to 70%...not quiet as high as the NHC's 90% as of this writing. While it is reasonable to have peak odds on the high side due to most global models developing this system into a tropical cyclone by day 5... I haven't gone quiet as high as the NHC in this update as the thunderstorm activity that has been suppressed to the south of the tropical wave has been disorganized. Need to see more organization in the thunderstorm activity before setting very high odds in future updates. Also this system may initially struggle with some easterly shear in the first part of the 5-day forecast period... with the forward speed of this disturbance slowing through 72 hours while the steering surface ridge initially has a gaping weakness caused by Hurricane Fiona and thus falling behind the upper easterly wind speed to be generated on the south side of the northern Caribbean upper ridge axis. The northward angle in the forecast track places this system more directly beneath the upper ridge axis by 96+ hours where wind shear would be low regardless of this system's forward speed... and this is when I have odds of tropical cyclone formation above the 50% mark (tropical cyclone formation more likely than not by this point).
Note that interests in northeastern Venezuela... Trinidad and Tobago... and the southern Lesser Antilles are likely to see gusty winds and heavy rains from this tropical wave by tonight regardless of tropical cyclone formation or not. Interests in Jamaica should monitor the progress of this tropical wave as it has potential to be near the area as a tropical cyclone by day 5.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Sep 22)...15% chance of tropical cyclone formation (just northeast of Tobago near 11.2N-60W)
IOH 48 Hr Outlook (0000Z Sep 23)...35% chance of tropical cyclone formation (eastern Caribbean Sea near 12.5N-64W)
IOH 72 Hr Outlook (0000Z Sep 24)...50% chance of tropical cyclone formation (central Caribbean Sea near 14.5N-67W)
IOH 96 Hr Outlook (0000Z Sep 25)...60% chance of tropical cyclone formation (central Caribbean Sea near 15.5N-71W)
IOH 120 Hr Outlook (0000Z Sep 26)...70% chance of tropical cyclone formation (southeast of Jamaica near 16.2N-75.5W)
AREA OF INTEREST #32... A vigorous tropical wave of low pressure over western Africa remains characterized by a gyre of thunderstorm activity... with the activity as of late biased to the west side of the gyre. Computer models insist that the tropical wave has potential to develop at an unusually north location offshore of Africa... between Mauritania and the Republic of Cabo Verde Islands... in approximately 72+ hours. While water temps in this area are currently above the 26 deg C threshold needed for tropical cyclone formation... tropical cyclone development is usually precluded in this region by dry Saharan air. However given the insistence shown in the global models... I have continued this tropical wave of low pressure as an area of interest on this blog and the tropical wave is now also an area of interest in the NHC tropical weather outlook. Due to the initially healthy organization of the wave and insistence of the models...my peak odds of tropical cyclone formation remain at 15%. The low odds are a reflection of the climatology that does not usually favor development here... and will only raise odds of development further should the tropical wave continue to produce an organized gyre of thunderstorms once it is offshore.
The eastern divergence zone of the current far eastern Atlantic upper trough has been keeping low surface pressures across northwestern Africa and the Iberian Peninsula of Europe. This low pressure field has allowed the tropical wave to have a north angle in track as it treks westward across Africa.. which is why it will emerge offshore at a more northern than usual position. Even though the Atlantic surface ridge is expected to remain intact in the long range... the models see that this system could quickly develop into a strong/tall enough circulation to continue angling north in track due to upper southwesterly flow on the north side of the tropical upper ridge in the region... and out ahead of a fragment of upper troughing to be left behind by the current eastern Atlantic upper trough. The upper southwesterly flow will produce some shear... however not too high to shunt tropical development... especially as the fragment of the cool core upper troughing is forecast to dissipate by day 4 while remaining cut-off from high-latitude cold air.
On a final note... should this system in fact become a tropical cyclone it has potential to kick up surf on the shores of the Republic of Cabo Verde Islands by Friday and this weekend.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Sep 22)...0% chance of tropical cyclone formation (western Africa near 14N-11W)
IOH 48 Hr Outlook (0000Z Sep 23)...0% chance of tropical cyclone formation (west coast of Africa near 15N-16W)
IOH 72 Hr Outlook (0000Z Sep 24)...10% chance of tropical cyclone formation (east of the Republic of Cabo Verde Islands at 16N-21W)
IOH 96 Hr Outlook (0000Z Sep 25)...15% chance of tropical cyclone formation (just north of the Republic of Cabo Verde Islands at 18N-24W)
IOH 120 Hr Outlook (0000Z Sep 26)...15% chance of tropical cyclone formation (eastern Atlantic near 21N-26.8W)
AREA OF INTEREST #33...A tropical wave of low pressure was observed to enter the eastern tropical Atlantic from western Africa on September 18. Since then the wave has organized into an east-west elongated tropical low pressure now located west-southwest of the Republic of Cabo Verde Islands. The elongated circulation appears to have slowed down its westward progress while entangled with the low pressure field over northwestern Africa and the Iberian peninsula of Europe... being generated by the eastern divergence zone of an upper trough in the region. The elongated circulation is also likely becoming increasingly entangled with a large tropical wave of low pressure that will soon emerge into the far eastern tropical Atlantic which is designated area of interest #32 on this blog. The CMC model has insisted on developing this low pressure circulation... and indeed the west side of the elongated circulation continues to fire organized shower and thunderstorm activity. I added this system as an area of interest during special update #106B on Tuesday evening... and as of 2 AM EDT the NHC has also added this area of interest to their tropical weather outlook product.
My forecast below assumes the west side of the elongated circulation... currently located near 10.5N-30W... will consolidate and gradually increase its forward speed while escaping the grip of area of interest #32. However the westward forward speed by day 5 is kept a little below the typical 5W longitude per day seen in the deep tropics... as the steering Atlantic surface ridge will be in a weakened state due to the sprawling circulation of what will be the remnant frontal cyclone of Fiona in the northwest Atlantic/Atlantic Canada region. Conditions are favorable for development as the tropical low will be embedded below a vast area of tropical upper ridging with low shear and upper outflow. And combined with the early signs of organization... I already have peak odds of tropical cyclone formation set at 30%. I have not assigned higher odds at this time as the CMC is the only global model showing this disturbance developing. Odds would be increased in future updates should other models join... or if observations suggest further organization/development.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Sep 22)...15% chance of tropical cyclone formation (eastern tropical Atlantic near 10.5N-32W)
IOH 48 Hr Outlook (0000Z Sep 22)...25% chance of tropical cyclone formation (eastern tropical Atlantic near 11N-34W)
IOH 72 Hr Outlook (0000Z Sep 24)...30% chance of tropical cyclone formation (eastern tropical Atlantic near 11.5N-37W)
IOH 96 Hr Outlook (0000Z Sep 25)...30% chance of tropical cyclone formation (central tropical Atlantic near 12N-41W)
IOH 120 Hr Outlook (0000Z Sep 26)...30% chance of tropical cyclone formation (central tropical Atlantic near 12.5N-45W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z (Sep 20) CMC Model Run...
**For Major Hurricane Fiona... passes just northwest of Bermuda at 72 hours... swings more north in track and moves into eastern Nova Scotia at 96 hours while transitioning into a large remnant frontal cyclone... while continuing northward across eastern Quebec and inland Labrdador the remannt frontal cyclone weakens through 120 hours.
**For Tropical Storm Gaston... arcs more east in track while reaching strong tropical storm strength and reaches 40N-35W at 54 hours... subsequently begins to weaken and stalls near 40.2N-33W at 78 hours... remnant low then curves west and north around the southwest quadrant of a northern surface ridge and reaches 32.5N-37W at 120 hours.
**For area of interest #30... tropical wave organizes into a tropical low near the ABC Islands (Aruba Bonaire and Curacao) at 54 hours... tropical low's center passes just offshore of Colombia through 78 hours... tropical cyclone formation suggested near 13N-74W through 96 hours... begins to strengthen futher while located just east of the Nicaragua/Honduras border at 126 hours.
**For area of interest #32... tropical wave emerges from west coast of Africa at 42 hours... tropical low moves nothwest and reaches 19.8N-23W at 120 hours.
**For area of interest #33...tropical cyclone formation suggested near 14N-37W at 96 hours... moves northwest to 16.2N-39.5W at 120 hours.
1200Z (Sep 20) ECMWF Model Run...
**For Major Hurricane Fiona... passes just northwest of Bermuda at 72 hours... swings more north in track and moves into eastern Nova Scotia at 96 hours while transitioning into a large remnant frontal cyclone... while continuing northward across eastern Quebec and inland Labrdador the remannt frontal cyclone weakens through 120 hours.
**For Tropical Storm Gaston... arcs eastward in track and then weakens to a remnant low just west of the Azores at 72 hours... remnant low begins to drift west-northwest away from the Azores and reaches 39.5N-35.5W at 120 hours.
**For area of interest #30...tropical cyclone formation suggested in the central Caribbean Sea near 15N-78.8W at 120 hours
**For area of interest #33...develops into a tropical low by 168 hours while located near 14N-37.5W at 168 hours.
1800Z (Sep 20) GFS Model Run...
**For Major Hurricane Fiona... passes just northwest of Bermuda at 66 hours... swings more north in track and moves into eastern Nova Scotia at 93 hours while transitioning into a large remnant frontal cyclone... while continuing northward across eastern Quebec and inland Labrdador the remannt frontal cyclone weakens through 120 hours.
**For Tropical Storm Gaston... reaches top-end tropical storm strength while arcing eastward in track and reaches 40.2N-34W at 48 hours... subsequently weakens with the remnant low stalling just west of the Azores at 72 hours... remnant low then curves west and north around the southwest quadrant of a northern surface ridge and reaches 33N-35W at 120 hours.
**For area of interest #30... tropical wave organizes into a tropical low just offshore of northeast Venezuela and jsut west of the southernmost Lesser Antilles at 39 hours... compact tropical cyclone formation suggested just north of the ABC Islands (Aruba Bonaire and Curacao) at 57 hours... only gradually strengthens and reaches 15N-78.5W at 120 hours.
**For area of interest #32... tropical wave emerges from west coast of Africa at 36 hours... organizes into a broad tropical low centered just east of the Republic of Cabo Verde Islands through 63 hours... tropical low turns north in track and becomes a tropical cyclone near 19.5N-21W at 90 hours... while remaining generally stationary in this area weakens to a remnant low through 120 hours
**For area of interest #33... no development shown
1800Z (Sep 20) NAVGEM Model Run...
**For Major Hurricane Fiona... center passes over Bermuda at 78 hours... swings more north in track and moves into Newfoundland 114 hours while transitioning into a large remnant frontal cyclone... remnant cyclone moves offshore of the northern Newfoundland coast through 120 hours.
**For Tropical Storm Gaston... arcs eastward in track and then as a remnant low stalls near 39.8N-32.5W at 78 hours... remnant low accelerates west and dissipates near 40N-40W just after 120 hours.
**For area of interest #30... tropical wave initialized as a tropical low near 9.9N-55W at at 0 hours... crosses the southern Lesser Antilles at 24 hours... while curving northwest and north toward ridge weakness created by Fiona the tropical low moves into the waters between Puerto Rico and Dominican Republic at 90 hours... tropical low dissipates shortly thereafter
**For area of interest #32... tropical wave emerges from west coast of Africa at 36 hours... sortly thereafter organizes into a tropical low that turns north-northwest and then north which moves into the southern Canary Islands by 120 hours.