*******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 26 2022 3:49 AM EDT...
Tropical Storm Ian has begun to quickly organize and strengthen in the western Caribbean Sea... will become a hurricane shortly. Ian is expected to bring impacts from the Cayman Islands to parts of the southeastern United States in the days ahead while at risk of strengthening into a strong hurricane... see Ian section below for more details.
Tropical Storm Gaston in the open north Atlantic dissipates into a remnant low while losing upper air support. Tropical Depression Hermine has also degenerated into a remnant low offshore of northwestern Africa. See remnants of Gaston and Hermine sections below for final statements on both systems.
In addition to the above systems... also monitoring multiple areas of interest as follows:
(1) See area of interest #33 section below for information on a tropical low pressure area expected to meander aimlessly in the eastern tropical Atlantic over the next 48 hours... after which time it will move northwestward into the open central Atlantic. This feature also has increased potential to become a tropical cyclone while having recently developed sustained thunderstorm activity.
(2) See area of interest #34 section below for more information on a potential tropical disturbance that could materialize offshore of western Africa in the days ahead.
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 is designated #33 and #34 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.
TROPICAL STORM GASTON (RECENTLY DOWNGRADED TO REMNANTS OF GASTON)... The cloud swirl of Gaston continues its westward trek in the open north Atlantic and around the south side of the steering Atlantic surface ridge. This is expected to continue as the western convergence zone of the far eastern Canada upper trough entangled with Fiona's remnants expands the surface ridge further westward... once this energy proceeds across the northwest Atlantic over the next 24 hours. Meanwhile Gaston has lost all thunderstorm activity as the upper trough that aided it yesterday has moved past it and joined the developing large-scale upper trough/vortex to the southeast. In addition the split flow upper divergence between the current northeast Atlantic upper ridge cell to the northeast and the upper trough/vortex feature to the southeast has developed north of instead of directly over Gaston... thus Gaston has run out of upper-level sources to enhance it while it remains over water temps below 26 deg C. Although split flow upper divergence may develop between southerlies on the east side of the upper trough energy to approach from Fiona's remnant system and northerlies streaming into the northwest quadrant of the upper trough/vortex feature... Gaston has moved a bit faster to the west such that it will also miss this split flow upper divergence area to the west by 24 hours. At 48+ hours... this upper trough energy also joins the large upper trough/vortex feature to the southeast and hence further expands it... and to the northwest a warm core upper ridge develops in the warm southerly flow ahead of the eastern US frontal system that will be coaxing Ian northward into the eastern Gulf of Mexico. Upper-level convergent flow on the northwest side of the upper trough/vortex and southeast side of the upper ridge should suppress Gaston in the longer range.
As of 11 PM EDT... Gaston's cloud swirl low pressure was downgraded to a remnant low as it continued to lack thunderstorms... and due to the above unfavorable upper-level wind outlook it is not expected to make a comeback. This is my final statement on Gaston on this blog as it is no longer a tropical feature.
TROPICAL STORM IAN... For much of Sunday the tropical storm that has been moving into the western Caribbean Sea appeared to continue growing in size while squalls of showers and thunderstorms began to cover Jamaica... the Cayman Islands... and much of Cuba. The activity appeared to be weighted to the east side of Ian's circulation due to a patch of upper vorticity to the west. Just before 0000Z... a burst of thunderstorm activity developed a little northeast of the previous forecast track... however it appears the broad surface circulation has quickly consolidated toward the burst. Ian is moving more north in track in response to the surface ridge weakness over the eastern US being generated by the eastern divergent side of a large upper trough moving into the area. Models have switched back to showing a further south reach of the upper trough and associated surface ridge weakness. And combined with the fact that Ian has recently consolidated north and east of the previous forecast track which places it even closer to the further south upper trough/surface ridge weakness... as feared in my previous update the forecast track has shifted back east. The implication is the Cayman Islands... the Florida Keys... and the west coast of the Florida peninsula are more likely to see notable impact from Ian (note that western Cuba will see impacts regardless of a further west or east track). Toward the latter part of the forecast period... models agree that the upper trough and associated surface ridge weakness gradually lift northeastward and away... trapping Ian south of a potent surface ridge that builds under the western convergence zone of the amplified departing upper trough. In addition the upper trough is expected to leave behind a cut-off trough over the southeastern US. Ian's northward speed is expected to slow in the 3 to 4 day timeframe...a combination of Ian being embedded in steering upper southerly flow ahead of the leftover cut-off upper trough while the potent surface ridge resists Ian's northward progress. Once the main upper trough and associated blocking surface ridge shift further east by day 5... a gradual increase in forward speed is likely.
Regarding the intensity forecast... things look ready for Ian to now take off with the circulation now consolidated underneath a compact and organized thunderstorm core. Moreover the disruptive patch of cool core upper vorticity to the west is in the process of dissipating while it has remained isolated from high-latitude cold air... which should allow Ian's upper outflow to expand in all quadrants of the circulation. Rather warm 29 to 30 deg C waters will also help Ian. These observations... combined with the fact that Ian is a touch stronger than my prior intensity forecast... cause me to raise the intensification rate of Ian for the next 24 hours relative to the prior forecast. However I still arrive to the same category 3 peak for my intensity forecast for the timeframe that is now 48 hours away because the upper trough over the eastern US is expected to have a further south reach... increasing the potential for southwesterly wind shear once Ian moves past western Cuba and into the southeastern Gulf of Mexico. For the leftover cut-off upper trough expected over the southeast US... models have also trended with a less amplified version of the trough which causes more southwesterly shear over Ian in the longer range as the trough nears... with the shear only worsening for Ian as it slows down and falls behind the upper southwesterly wind speed. Therefore I have opted for a slightly faster decay rate of Ian after 48 hours... with the weakening rate accelerated from 96 to 120 hours due to landfall in the northwest corner of the Florida peninsula or far east end of the Florida panhandle.
Regarding impacts to land areas:
(1) Coastal sea swells are possible for Jamaica... north coast of Honduras... and north coast of the Mexican Yucatan peninsula province of Quintana Roo as Ian intensifies. Swells are less likely for Belize due to the eastward shift in the forecast track.
(2) Interests in the Cayman Islands should have completed preparations for Ian by now. On the latest forecast track... tropical storm conditions (heavy rain... gusty winds with some damage potential... and coastal surf) should arrive to Little Cayman and Cayman Brac over the next 12 hours. Stronger hurricane-force conditions are possible further west... at Grand Cayman... during this time.
(3) Western Cuba will see tropical storm force conditions (heavy rain with flooding potential... gusty winds with some damage potential... and coastal surf) from Monday night to Tuesday night. Life-threatening coastal storm surge and wind is possible for the Isle of Youth and western Cuban mainland in the vicinity of the isle as Ian is expected to move into the area as a strengthening category 2 hurricane. The threat of life-threatening wind and coastal storm surge has reduced a little for the western tip of Cuba due to the latest east shift in the forecast track... however remain on guard here for such conditions in case Ian wobbles more west in track on its approach into the region. I recommend preparations for Ian should be finished here by midday later today.
(4) For the Florida Keys... there is potential for Ian's center to pass over or just west of the westernmost Keys on Tuesday night as a major category 3 hurricane. This will subject the Keys to life-threatening coastal storm surge and wind and I recommended preparing for this worst-case scenario. I recommend preparations to be completed here by late tonight.
(5) For the Florida peninsula... the east side of Ian is expected to overspread the area late Tuesday further south... and the entire peninsula by Wednesday. The expected slow down in the forward speed will subject the peninsula to prolonged impacts such as high rainfall totals creating a risk of major flash flooding. Ian's center is expected to be located just offshore of the west coast of the peninsula... subjecting this side of coastline to a long period of onshore pushing wind and coastal storm surge. Based on the latest forecast track... the largest potential for damage from prolonged exposure to hurricane-force wind and storm surge on the west coast is from the Tampa Bay area and points north. The east side of peninsula could also be near enough to Ian's center to experience tropical storm force gusts with some damage potential... particularly north of Miami all the way to the Florida/Georgia border. I recommend preparing now for the above-listed impacts... with preparations finishing by late tonight further south and by midday Tuesday further north.
(6) The Florida panhandle should continue to monitor the progress of Ian. If the current forecast track holds... expect coastal surf across all of the panhandle... and tropical storm force winds with some damage potential in the eastern half of the panhandle by Wednesday and Thursday. The eastern half of the panhandle may also see a prolonged period of heavy rainfall with significant flash flooding potential due to the storm's forecast slow motion. Be ready to prepare Monday night through Tuesday.
(7) On the latest forecast track... the potential for impacts to southern Alabama is reducing. Southern Georgia can expect a prolonged period of heavy rainfall with significant flash flooding potential due to the storm's forecast slow motion... as well as tropical storm force winds with some damage potential by late Wednesday through Friday. In southern Georgia... be ready to prepare Monday night through early Wednesday.
Update of 2 AM EDT... Ian has strengthened further to 70 mph maximum sustained winds and will likely become a hurricane later this morning. Since the forecast below already anticipates a rapid strengthening rate today... making no changes to the intensity forecast at this time.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0000Z Sep 26)...65 mph maximum sustained wind tropical storm centered west-southwest of Jamaica and south of the Cayman Islands at 17.3N-81.4W
IOH 24 Hr Forecast (0000Z Sep 27)...105 mph maximum sustained wind hurricane centered just south of the Isle of Youth of western Cuba at 20.5N-82.8W
IOH 48 Hr Forecast (0000Z Sep 28)...120 mph maximum sustained wind major hurricane centered just west of the Florida Keys at 24.5N-83W
IOH 72 Hr Forecast (0000Z Sep 29)...105 mph maximum sustained wind hurricane centered just offshore of Tampa Bay Florida at 27.5N-83W
IOH 96 Hr Forecast (0000Z Sep 30)...80 mph maximum sustained wind hurricane centered just northwest of Tampa Bay Florida and just offshore of the northwestern Florida peninsula at 28.5N-83W
IOH 120 Hr Forecast (0000Z Oct 1)...50 mph maximum sustained wind tropical storm centered over the Florida/Georgia border at 30.5N-83W
REMNANTS OF HERMINE... Shortly after full update #111 was posted on the home page of this site on early Sunday... Tropical Depression Hermine offshore of northwestern Africa was downgraded to a remnant low as it collapsed over water temps below 26 deg C... under southwesterly shear imparted by the large upper trough consolidating in the region... and within a stable dry Saharan air mass. The remnant low is also now inconsequential impact-wise... and this is my final statement on Hermine on this blog as it is no longer a tropical feature.
AREA OF INTEREST #33...The wandering tropical low pressure spin in the eastern Atlantic has developed persistent thunderstorm activity in the north side of its circulation. It is interesting that the activity is weighted to the north side of the circulation when considering the current absence of shear below the tropical upper ridge axis in the region... and that the activity has developed toward instead of away from dry Saharan air which is seen as a beige tint in true-color visible satellite (before sunset). The tropical low has also moved a little more toward the northeast than I previously anticipated and toward a broad area of low surface pressure to the northeast... which contains Hermine's remnants... and is supported by divergence on the east side of a large-scale upper trough that has consolidated in the region. My updated forecast track is adjusted based on the current position of the tropical low's center... which is near 14.5N-35.5W as of this writing. Because some additional northward drift and into the thunderstorm activity was seen in recent satellite animation... I anticipate that this system drifts a little more to the north or northeast toward 15N-35W where it then stalls... as this location is a saddle point of conflicting steering between the broad low pressure area to the northeast and Atlantic surface ridge that has been trying to push this system west.
After 48 hours... the large-scale cold core upper trough in the region is expected to weaken while remaining isolated from cold air thanks to the ongoing warm core north Atlantic upper ridge. The upper ridge will also break the weakening trough into a series of upper vortices that retrograde southwestward around the ridge. As the cold core upper trough and associated surface low pressure area to the northeast weakens... the Atlantic surface ridge will finally try to push this system west by 72+ hours. However an increasing north angle is depicted in the developing west track as the surface ridge will develop a weakness to the northwest as the current frontal system over the eastern US will have moved offshore. And should this system in fact becoming a stronger/taller tropical cyclone... the upper southwesterly flow ahead of one of the decaying upper vortices would also coax this system on a more northward track. The upper southwesterly flow is expected to become a detriment to this system in the long range by shearing it.
I agree with the NHC's recent 2 AM EDT assessment in raising tropical cyclone formation odds as the recent thunderstorm activity in the circulation has been quiet persistent. However I do not quiet agree on raising odds to the NHC's 50% mark just yet... would like to see the thunderstorm activity persist longer and also get better organized... an so my short-term odds of development are raised to 40%. Although there is dry Saharan air just to the northeast of this system... I do not expect a total defeat of this system from dry Saharan air as the broad low pressure area to the northeast may slow the westward transport of additional Saharan air toward this system. I lower development odds after 48 hours as this system moves into increasing southwesterly shear (see end of previous paragraph for the source of the shear).
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Sep 27)...40% chance of tropical cyclone formation (eastern tropical Atlantic near 15N-35W)
IOH 48 Hr Outlook (0000Z Sep 28)...40% chance of tropical cyclone formation (eastern tropical Atlantic near 15N-35W)
IOH 72 Hr Outlook (0000Z Sep 29)...30% chance of tropical cyclone formation (eastern tropical Atlantic near 16N-37.5W)
IOH 96 Hr Outlook (0000Z Sep 30)...10% chance of tropical cyclone formation (central tropical Atlantic near 19N-41W)
IOH 120 Hr Outlook (0000Z Oct 1)...0% chance of tropical cyclone formation (central Atlantic near 22N-44W)
AREA OF INTEREST #34...A tropical wave of low pressure just offshore of Africa has stalled in weak steering currents caused by a broad low pressure area that contains Hermine's remnants. An additional tropical wave of low pressure over western Africa... in the vicinity of 7.5W longitude... will merge with the offshore wave over the next 48 hours.. potentially resulting in a broad offshore tropical disturbance. After this time... any broad disturbance that develops should begin to slide westward as the broad low pressure to the north dissipates as the large-scale upper trough generating it should begin to weaken and retrograde westward and away around the current north Atlantic upper ridge. The broad low pressure will be replaced by the recovering eastern nose of the Atlantic surface ridge that should push this disturbance westward. There is potential for this disturbance to develop due to low shear and upper outflow provided by a persistent tropical upper ridge in the region. I have set peak odds of development at a low 10% as the pair of seedling tropical waves have seen a recent decline in thundrestorm activity... and the more reliable GFS and ECMWF models do not show development of this disturbance (instead the CMC and NAVGEM showed development).
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Sep 27)...0% chance of tropical cyclone formation (western Africa near 10N-12.5W)
IOH 48 Hr Outlook (0000Z Sep 28)...0% chance of tropical cyclone formation (just offshore of western Africa near 10.5N-17.5W)
IOH 72 Hr Outlook (0000Z Sep 29)...10% chance of tropical cyclone formation (eastern tropical Atlantic near 11N-21W)
IOH 96 Hr Outlook (0000Z Sep 30)...10% chance of tropical cyclone formation (eastern tropical Atlantic near 11.5N-25.5W)
IOH 120 Hr Outlook (0000Z Oct 1)...10% chance of tropical cyclone formation (eastern tropical Atlantic near 11.5N-30W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z (Sep 25) CMC Model Run...
**For Tropical Storm Gaston... weakens to a remnant low near 38.5N-38.5W at 18 hours... remnant low weakens to a trough near 37.5N-42W at 42 hours.
**For Tropical Storm Ian... passes just west of the Cayman Islands at 24 hours... center crosses the western tip of Cuba at 42 hours... becomes a hurricane at 66 hours while center located west-northwest of the Florida Keys... while just offshore of the northwest Florida peninsula coastline weakens to a high-end tropical storm at 114 hours... center moves ashore at the east end of the Florida panhandle at 126 hours resulting in a faster weakening rate.
**For area of interest #33... tropical low begins drifting westward and reaches 13.8N-38.5W at 54 hours... tropical low subsequently accelerates on a faster northwest track and reaches 19.5N-37.5W at 120 hours
**For area of interest #34... broad tropical low becomes better defined near 11N-21.5W at 120 hours... while continuing west tropical low becomes better organized and reaches 13.2N-29.5W at 168 hours.
1200Z (Sep 25) ECMWF Model Run...
**For Tropical Storm Gaston... weakens to a remnant low near 38N-39.5W at 24 hours... accelerates west-southwest where it weakens to a remnant trough near 34.5N-32.5W at 72 hours.
**For Tropical Storm Ian... strengthens into a hurricane at 48 hours while moving northward into western Cuba... center of intensifying hurricane passes just west of the Florida Keys between 48 and 72 hours... as a potentially intense hurricane the center is located just offshore of the southwestern Florida peninsula near 25.5N-82.8W at 72 hours... while weakening the hurricane center moves into Tampa Bay Florida at 96 hours... weakens to an inland tropical storm over the northern Florida peninsula at 120 hours while centered near 30N-83W at 120 hours.
**For area of interest #33... tropical low remains stationary through 48 hours... moves north-northwest and weakens to a trough near 17.5N-38.5W at 96 hours.
**For area of interest #34... no development shown
1800Z (Sep 25) GFS Model Run...
**For Tropical Storm Gaston... weakens to a remnant low near 37.5N-41.2W at 27 hours... weakens to a trough near 35.2N-51.5W at 60 hours.
**For Tropical Storm Ian... passes just west of the Cayman Islands at 24 hours as a strong tropical storm... moves north into western Cuba at 39 hours while strengthening into a hurricane... passes just west of the Florida Keys at 51 hours... beginning at 78 hours begins to wobble more slowly northward offshore of the northwestern Florida peninsula coast while also starting a gradual weakening phase... makes landfall at the east end of the Florida panhandle at 120 hours as a minimal hurricane.
**For area of interest #33... tropical low remains stationary through 48 hours... moves north-northwest and weakens to a trough near 20N-42W at 111 hours.
**For area of interest #34... no development shown
1800Z (Sep 25) NAVGEM Model Run...
**For Tropical Storm Gaston... weakens to a remnant low near 38N-40W at 18 hours... weakens to a trough near 36.2N-43W at 42 hours.
**For Tropical Storm Ian... passes just west of the Cayman Islands at 30 hours... strengthens briskly into a hurricane with the center crossing western Cuba at 48 hours... passes just west of the Florida Keys at 60 hours... makes landfall over the western Florida panhandle at 114 hours... while beginning to weaken inland the hurricane moves into southern Alabama at 120 hours.
**For area of interest #33... tropical low remains stationary over next 54 hours after which time it dissipates.
**For area of interest #34... broad tropical low becomes better defined near 12.5N-20W at 126 hours... becomes a tropical storm over the southern Republic of Cabo Verde Islands at 168 hours.