*******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.**********
...THURSDAY SEPTEMBER 22 2022 5:20 AM EDT...
URGENT - Tropical Storm Gaston now expected to move across the Azores while maintaining its current strength and tropical characteristics. The Azores only have approximately 12 hours to prepare. See Gaston section below for more information.
Major Hurricane Fiona is now midway between Bermuda and the Bahamas. 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.
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 across the southeastern Caribbean Sea. There is an high risk this wave develops into a tropical cyclone that moves across the central and eastern Caribbean Sea in the long range... interests in Jamaica... the Cayman Islands... and western Cuba need to be aware of this system.
(2) See area of interest #32 section below for a tropical wave of low pressure being monitored for signs of development in the far eastern Atlantic waters offshore of west-central and northwest Africa.
(3) See area of interest #33 section below for a tropical low pressure area west-southwest of the Republic of Cabo Verde Islands that continues to show 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 #30... #32... and #33 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... The western outflow of Hurricane Fiona has become restricted by upper southwesterly flow in advance of a cut-off upper trough currently just offshore of the southeastern United States. The outflow blockage is likely why Fiona stopped intensifying... however the blockage has also not been enough to weaken the hurricane either such that it remains an intense category 4 with 130 mph maximum sustained winds. The upper southwesterly flow has also lifted the hurricane northward into the waters midway between Bermuda and the Bahamas. I have nudged my updated forecast track slightly northward due to the current position of Fiona relative to the previous forecast. In the next 24 hours... the track is expected to buckle more eastward once the cut-off upper trough to the west gets pushed closer to Fiona by a major upper trough currently approaching from central Canada. After 24 hours... the track is expected to bend more north and less east as Fiona gets funneled into the southerly flow out ahead of the major 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 48 and 72 hours swings northwest in track... right into Atlantic Canada... while whirling into the center of the forming upper vortex.
Regarding forecast intensity... I have nudged my updated forecast upward just slightly due to Fiona's current strength relative to the previous forecast. Going forward... the increasing upper southwesterly flow in Fiona's environment should work against the hurricane by moreso blocking its western outflow and perhaps lightly shearing it. However the shear would be mitigated as Fiona eventually accelerates northeast in the direction of the upper flow in the next 24 hours which is why I depict a slow weakening rate. At 24+ 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 Bahamas should gradually wind down as Fiona pulls northward and away.
(2) Fiona will bring 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 noon local time later today.
(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 now if you have not started preparing yet... finish preparations by Friday evening.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0000Z Sep 22)...130 mph maximum sustained wind major hurricane centered at 26.6N-71.2W
IOH 24 Hr Forecast (0000Z Sep 23)...120 mph maximum sustained wind major hurricane centered west-southwest of Bermuda at 31.5N-69W
IOH 48 Hr Forecast (0000Z Sep 24)...105 mph maximum sustained wind hurricane centered at 41.5N-60.5W
IOH 72 Hr Forecast (0000Z Sep 25)...Hurricane-force remnant frontal cyclone centered in the northwestern Gulf of St. Lawrence at 48N-62.5W
TROPICAL STORM GASTON...Gaston is a curious tropical storm while strengthening further to 65 mph maximum sustained winds... and then maintaining that strength instead of weakening while accelerating eastward over waters below 26 deg C. Typically tropical cyclones that develop over waters below 26 deg C require compensating cold upper air temperatures to de-stabilize the environment. However the 200 mb heights in Gaston's environment are around 1230 dekameters... would like to see lower heights closer to 1200 before calling a cold upper air environment. Noting that Gaston has been underneath the eastern upper divergence zone of a shortwave upper trough incoming from the west... and it is probable that this is where Gaston is getting its support from. Normally tropical cyclones that interact with upper troughs in this way... especially over water temps below 26 deg C... would transition into a non-tropical frontal low or cyclone. With Gaston... that has only happened to only a slight degree with a frontal-like cloud band extending southeast from Gaston's circulation... otherwise Gaston remains tropical with a core of showers and thunderstorms ongoing over and close to the center. It is probable then that the shortwave upper trough that is aiding Gaston and its thunderstorm core does not have cold enough air to erode the thunderstorm core...and thus Gaston continues on as a tropical storm over water temps below 26 deg C and under upper air temps that are not cold enough for de-stabilization. Gaston reminds me of Tropical Storm Theta which maintained strength and tropical characteristics for some time in November 2020 under rather similar circumstances.
Models have shifted east and now bring Gaston directly into the Azores. This makes sense with the above current outlook on Gaston... as Gaston is now poised to remain coupled with its supporting eastward-moving shortwave upper trough as long as the shortwave upper trough does not change. And with the eastward track implying that Gaston will remain over similar water temps that it is currently over... I now forecast Gaston to keep both its current strength and tropical characteristics on its way into the Azores. Between 24 and 48 hours... there is some southward angle in the forecast track of Gaston as the east side of Fiona and east side of the sprawling frontal low currently approaching the north Atlantic from eastern Canada will pull plenty of warm air northward into the far north Atlantic... resulting in the amplification of a far north Atlantic warm core upper ridge that in turn pushes Gaston's supporting shortwave upper trough on a more southward angle. The amplified north Atlantic upper ridge will also push the current north Atlantic upper trough southeastward into Europe... with the European upper trough and Gaston's shortwave upper trough merging into a southwest-northeast elongated string of upper vorticity between 48 and 72 hours. This will finally bring an end to the shortwave's supportive eastern divergence zone... and Gaston should finally lose its thunderstorms over the below-26 deg C water and weaken to a shallow remnant low that begins to reverse southwest and westward in track while steered by the surface ridge currently building to the north.
With this updated forecast... expect coastal sea swells and tropical storm force winds with some damage potential to increase across the Azores in the next 24 hours. Interests here will have approximately the next to 12 hours to make preparations.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0000Z Sep 22)...65 mph maximum sustained wind tropical storm centered at 39.6N-38W
IOH 24 Hr Forecast (0000Z Sep 23)...65 mph maximum sustained wind tropical storm centered just north of the westernmost Azores at 40.2N-31W
IOH 48 Hr Forecast (0000Z Sep 24)...65 mph maximum sustained wind tropical storm centered over the eastern Azores at 38N-26W
IOH 72 Hr Forecast (0000Z Sep 25)...Remnant low centered south of the Azores at 35.5N-27.5W
AREA OF INTEREST #30...The tropical wave of low pressure that was bearing down on northeastern Venezuela... Trinidad and Tobago... and southern Lesser Antilles has made its way into the southeast periphery of the Caribbean Sea. Northeasterly upper shearing flow on the southeast side of the current north Caribbean upper ridge axis has kept the squalls of showers and thunderstorms biased to the south side of the tropical wave. The activity currently covers parts of northeastern Venezuela... and up until recently has been disorganized. The more recent satellite frames suggest the activity is now organizing into spiral banding features. Based on the curvature of these features... it appears the area of maximum spin associated with the tropical wave of low pressure was near 11.5N-62.5W as of 0000Z earlier this evening. This is west of the previous forecast track... and so my updated one is adjusted westward. There is also a southward adjustment to the forecast track as this system has not yet responded to the surface ridge weakness associated with Hurricane Fiona. Models agree on a general west-northwest track across the Caribbean due to this ridge weakness at first. Once this weakness closes with Fiona's northward and away lift in track... the current northwest US upper vortex 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 that continues the west-northwest track of this system. While nearing the weakness... the north angle of the forecast track increases by day 5.
Regarding odds of tropical cyclone formation... I have slightly lowered the short-term odds as the thunderstorm activity for much of the last 24 hours was disorganized. My longer term odds of development are capped at 70%... below the NHC's 90% as of this writing. It remains to be seen if the current recent increase in the organization of the thunderstorms persists before I declare higher development odds. The northward angle in the forecast track places this system more directly beneath the upper ridge axis by 72+ hours...bringing an end to the northeasterly wind shear. This is when I have odds of tropical cyclone formation above the 50% mark (tropical cyclone formation more likely than not by this point).
Regarding impacts to land areas:
(1) Heavy rains and gusty winds currently occurring over northeastern Venezuela will likely spread westward across northwestern Venezuela... the Guajira peninsula of northern Colombia... and Aruba Bonaire and Curacao (ABC islands) over the next couple of days.
(2) Interests in Jamaica... the Cayman Islands... and western Cuba should monitor the progress of this tropical wave as it has high potential to be near the area as a strengthening tropical cyclone by days 4 to 6.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Sep 23)...25% chance of tropical cyclone formation (just northeast of Aruba Bonaire and Curacao near 12.5N-67.5W)
IOH 48 Hr Outlook (0000Z Sep 24)...45% chance of tropical cyclone formation (south-central Caribbean Sea near 13.5N-71W)
IOH 72 Hr Outlook (0000Z Sep 25)...60% chance of tropical cyclone formation (central Caribbean Sea near 14.5N-75.5W)
IOH 96 Hr Outlook (0000Z Sep 26)...70% chance of tropical cyclone formation (southwest of Jamaica near 16.2N-79.5W)
IOH 120 Hr Outlook (0000Z Sep 27)...70% chance of tropical cyclone formation (just southwest of the Cayman Islands near 18.8N-82.5W)
AREA OF INTEREST #32... A vigorous tropical wave of low pressure has been moving west-northwest across western Africa. The north angle in the track is induced by a surface low pressure field over northwest Africa and Iberian Peninsula of Europe by an upper trough in the region. The tropical wave has featured an area of rotation over the last few days... the center of which is now over northern Senegal near 14.5N-15W. Various model runs insist that the area of rotation will quickly develop into a tropical cyclone after it moves offshore... becoming strong/tall enough to sharply turn north while coupling with the upper flow on the east side of the aforementioned upper trough in the region... particularly as the upper trough leaves behind a fragment in the environment of this system. It is peculiar that multiple models suggest that even after moving north into water temps below 26 deg C offshore of northwestern Africa that this system is shown in some of the models maintaining both its strength and tropical characteristics while supported by the eastern divergence zone of the upper trough fragment... especially as the upper trough fragment is not particularly cold to de-stabilize the atmosphere. However reference the above Tropical Storm Gaston discussion about how this is possible... and we could simply be repeating Gaston all over again with this system. Note that after the upper trough fragment dissipates by day 3 while it remains cut-off from high latitude cold air... models quickly replace it with a more substantial upper trough that is a fusion between the current north and northwestern Atlantic upper troughs... and the shortwave upper trough currently interacting with Gaston. These troughs fuse together under the force of the north Atlantic warm upper ridge forecast to develop (see Gaston section for more information on this ridge). Essentially with the replacement upper trough at days 4 and 5... this system could repeat what Gaston is doing now all the way through day 5.
However unlike Gaston... the models are developing and maintaining this system offshore of northwestern Africa... a climatologically unusual place for tropical cyclones to exist due to dry Saharan air. Indeed just before sunset... the circulation of the tropical wave was observed to kick up a shelf of dry Saharan air in the vicinity of Mauritania and Western Sahara. And nighttime infrared satellite over the last several hours suggested that the dry Saharan air may be suppressing thunderstorm activity over and north of the center of circulation... as only scattered thunderstorm activity is currently present due south of the center. Therefore I retain a low 15% peak odds of tropical cyclone formation unless future observations warrant otherwise. With this paradigm... my forecast track has a more west and less north angle while assuming a weaker/shallower system more coupled to the surface flow around the Atlantic surface ridge instead of the upper flow being induced by the upper trough in the region. The forecast track points are also adjusted north and west of my previous forecast track due to the current position of the center of rotation. The updated track places this system under hostile westerly shear on the south side of the more substantial upper trough to become established in the region by days 4 and 5... therefore I end the outlook below with 0% odds at day 4.
On a final note... should this system in fact become a tropical cyclone as various models are suggesting... it has potential to kick up surf on the shores of the Republic of Cabo Verde Islands... Senegal... Mauritania... and Western Sahara by Friday and through early next week.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Sep 23)...5% chance of tropical cyclone formation (eastern tropical Atlantic near 15.5N-19.5W)
IOH 48 Hr Outlook (0000Z Sep 24)...15% chance of tropical cyclone formation (just north of the northeastern Republic of Cabo Verde Islands near 18N-23W)
IOH 72 Hr Outlook (0000Z Sep 25)...15% chance of tropical cyclone formation (northwest of the Republic of Cabo Verde Islands near 20N-26W)
IOH 96 Hr Outlook (0000Z Sep 26)...0% chance of tropical cyclone formation (eastern Atlantic near 22N-29.5W)
AREA OF INTEREST #33...The tropical low pressure west-southwest of the Republic of Cabo Verde Islands continues to show signs of organization while firing thunderstorm activity over and just northwest of its center of circulation currently near 10.5N-32.5W... albeit the intensity of the thunderstorms waxes and wanes instead of remaining steady such that a tropical cyclone has not formed. The westward progress of this system around the Atlantic surface ridge has been slow while it gets tugged by the large circulation of area of interest (AOI) #32 to the east. Finally multiple models are joining the CMC in showing this system as a trackable feature... and the emerging consensus is that this system will at first continue its slow west drift... and then take a peculiar eastward reversal back toward the eastern tropical Atlantic by the end of the five day forecast period which is an unusual track for this part of the Atlantic basin. However these solutions seem increasingly reasonable as the apparent distance between AOI #32 and this system has been decreasing as AOI #32 is located further west and is already on the west coast of Africa. What may help with the eastward reversal in the track is a substantial upper trough to interact with AOI #32 by days 4 and 5 whose eastern divergence zone will help AOI #32 build an expanding surface ridge weakness to the northeast. Even without the expanding surface ridge weakness... if indeed this system goes on to become a tropical cyclone it could be strong/tall enough to couple with upper westerly steering flow associated with the substantial upper trough. With these observations... I show a slower westward forward speed in my updated forecast track. If the model solutions don't budge in future updates... will have to consider reversing the track back east in the longer range. I have raised my peak odds of tropical cyclone formation to 40% due to the ongoing signs of organization associated with this disturbance.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Sep 23)...30% chance of tropical cyclone formation (eastern tropical Atlantic near 11N-34W)
IOH 48 Hr Outlook (0000Z Sep 24)...40% chance of tropical cyclone formation (eastern tropical Atlantic near 11.5N-36W)
IOH 72 Hr Outlook (0000Z Sep 25)...40% chance of tropical cyclone formation (eastern tropical Atlantic near 12N-38W)
IOH 96 Hr Outlook (0000Z Sep 26)...40% chance of tropical cyclone formation (central tropical Atlantic near 12.5N-40W)
IOH 120 Hr Outlook (0000Z Sep 27)...40% chance of tropical cyclone formation (central tropical Atlantic near 12.5N-41W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z (Sep 21) CMC Model Run...
**For Major Hurricane Fiona... passes just northwest of Bermuda at 48 hours... swings more north in track and moves into eastern Nova Scotia at 66 hours while transitioning into a large remnant frontal cyclone... while continuing northward across eastern Quebec... inland Labrador and into northeastern Canada the remnant frontal cyclone weakens to a frontal low through 120 hours.
**For Tropical Storm Gaston... begins weakening at 48 hours while centered just northwest of the westernmost Azores near 40N-31.5W... weakening remnant low turns south... west... then north and reaches 41.2N-37W at 120 hours.
**For area of interest #30... tropical cyclone formation suggested near 15N-78W at 90 hours... center curves more northwest in track and passes just west of the Cayman Islands through 120 hours while strengthening into a hurricane.
**For area of interest #32... tropical wave emerges from west coast of Africa at 18 hours... through 42 hours organizes into a broad tropical low between the west coast of Africa and Republic of Cabo Verde Islands... tropical low moves northwest and passes just northeast of the Republic of Cabo Verde Islands through 72 hours... weakening tropical low turns more west in track and reaches 20N-26W at 120 hours.
**For area of interest #33... tropical low reaches 12.5N-39W thorugh 90 hours... while coming under the grip of area of interest #32 the tropical low slows down and drifts east... tropical cyclone formation suggested near 14N-38W at 132 hours.
1200Z (Sep 21) ECMWF Model Run...
**For Major Hurricane Fiona... passes just northwest of Bermuda at 48 hours... swings more north in track and moves into eastern Nova Scotia at 72 hours while transitioning into a large remnant frontal cyclone... while continuing northward across eastern Quebec... inland Labrador and into the waters just offshore of northeastern Canada the remnant frontal cyclone weakens to a frontal low through 120 hours.
**For Tropical Storm Gaston... strengthens further while reaching waters just north of the Azores at 48 hours... strong circulation dives south across the Azores between 48 and 72 hours... accelerates west-southwestward as a weakening remnant low which reaches 35.5N-39W at 120 hours.
**For area of interest #30...tropical cyclone formation suggested near 15N-78W at 96 hours... quickly intensifies into a strong tropical storm just south of the Cayman Islands at 120 hours.
**For area of interest #32... tropical wave organizes into a tropical low just offshore of Senegal at 24 hours... after 48 hours turns north-northwest in track while intensifying into a moderate tropcial storm that reaches 20.2N-22W at 72 hours... while maintaining strength reaches waters just southwest of the Canary Islands near 27N-20.5W at 120 hours
**For area of interest #33... no development shown
1800Z (Sep 21) GFS Model Run...
**For Major Hurricane Fiona... passes just northwest of Bermuda at 42 hours... swings more north in track and moves into eastern Nova Scotia at 66 hours while transitioning into a large remnant frontal cyclone... while continuing northward across eastern Quebec... inland Labrador and into the waters just offshore of northeastern Canada the remnant frontal cyclone weakens to a frontal low through 120 hours.
**For Tropical Storm Gaston... maintains strength while curving east and then south into the western Azores through 51 hours... shortly thereafter begins weakening while reversing on a westward track... remnant low reaches 32.5N-40.2W at 120 hours.
**For area of interest #30... tropical cyclone formation suggested near 14.5N-79.5W at 84 hours... strengthens further while moving into the western Caribbean and reaches 18.2N-85W at 120 hours
**For area of interest #32... tropical wave moves offshore of western Africa at 9 hours... tropical cyclone formation suggested at 15N-20W at 36 hours... abruptly turns north-northwest and reaches top-end tropical storm strength while reaching 20.1N-21W at 63 hours... finally begins to weaken over cooler water at 102 hours while near 24N-20.2W... remnant low located just southwest of the Canary Islands at 123 hours.
**For area of interest #33... tropical low located near 12.5N-36.2W at 87 hours... while coming under the grip of area of interest #32 the tropical low slows down and drifts east... tropical cyclone formation suggested near 14.5N-35W at 135 hours... continues drifting east-northeast as a weak tropical cyclone while under the tug of an additional tropical wave that emerges from the west coast of Africa with the tropical low reaching 16.5N-34W at 168 hours.
**Additional tropical wave emerges from west coast of Africa at 117 hours... develops into a tropical depression centered just south of the southwestern Republic of Cabo Verde Islands at 168 hours.
1800Z (Sep 21) NAVGEM Model Run...
**For Major Hurricane Fiona... passes just northwest of Bermuda at 42 hours... swings more north in track and moves into eastern Nova Scotia at 72 hours while transitioning into a large remnant frontal cyclone... while continuing northward across eastern Quebec... inland Labrador and into the waters just offshore of northeastern Canada the remnant frontal cyclone weakens to a frontal low through 120 hours.
**For Tropical Storm Gaston... moves east-northeast and then east-southeast such that it moves into the Azores by 48 hours... accelerates westward while weakening to a remnant low soon after... remnant low weakens to a trough near 35.5N-37.5W at 120 hours.
**For area of interest #30... tropical wave develops into a tropical low over the southeastern Caribbean Sea near 12.5N-65W at 24 hours... moves northwest into the waters offshore of southern Haiti/Dominican Republic through 66 hours due to ridge weakness caused by Fiona... after the weakness closes the tropical low moves west-northwest while becoming larger and broader over eastern Cuba at 90 hours... the broadening low loses its definition shortly thereafter.
**For area of interest #32... tropical wave emerges from west coast of Africa at 12 hours... through 30 hours organizes into a broad tropical low between the west coast of Africa and Republic of Cabo Verde Islands... tropical low subsequently turns north and dissipates just south of the Canary Islands at 120 hours.