*******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.**********
...THURSDAY SEPTEMBER 15 2022 2:20 AM EDT...
The tropical wave of low pressure in the open central Atlantic has spent Wednesday developing into Tropical Depression Seven and now Tropical Storm Fiona. See Fiona section below for more information on the new tropical storm and its potential impacts to the northern Caribbean Islands and eastern Bahamas within the next five days. See area of interest #29 and #30 sections below for an update on the pair of trailing tropical waves of low pressure located well east of Tropical Storm Fiona.
Elsewhere... a broad tropical disturbance could materialize over the western Caribbean... Bay of Campeche... southeastern Mexico... western Central America... and far eastern Pacific within the next four days as follows:
(1) A surface trough of low pressure currently located over the southwestern edge of the Gulf of Mexico and the outflow of a current upper ridge over southeastern Mexico/western Central America are already producing a broad area of low clouds and scattered thunderstorms.
(2) Upper vorticity in the Caribbean is expected to gradually fade while remaining cut-off from high-latitude cold air... with whatever remains of that upper vorticity to get swept up into an upper trough fragment to become cut-off over the southeastern United States. The removal of Caribbean upper vorticity will potentially allow the upper ridge in the region to expand. At the surface... the tail end of the cold front currently in the northeastern Gulf of Mexico... the current southwestern Gulf of Mexico surface trough... and the current tropical wave approaching from the central Caribbean Sea may merge into a broad tropical low pressure area supported by the expanding upper ridge's outflow. The broad tropical low pressure area would span the western Caribbean... Bay of Campeche... southeastern Mexico... western Central America... and far eastern Pacific.
(3) After four days... the most recent model runs suggest a southward shift of the tropical upper ridge toward the eastern Pacific as the cut-off upper trough over the southeastern United States amplifies southward into the eastern Gulf of Mexico due to a more amplified upper ridge building over the United States. This suggests the broad tropical low pressure area will more likely develop in the eastern Pacific instead of the western Caribbean or Bay of Campeche.
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 and #30 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 thunderstorm activity on the east side of Tropical Depression Seven has continued to grow in size as well as intensity when studying infrared satellite imagery. Moreover the NHC is citing satellite scans of surface winds that show the depression is now Tropical Storm Fiona with 50 mph maximum sustained winds. Downstream and well to the west... the current upper trough over eastern North America will later leave behind a cut-off upper trough over the southeastern United States whose eastern divergence zone will support an offshore cold front/inverted surface trough. The Atlantic surface ridge will also be intact to the north of Fiona... therefore the track going forward is expected to be west to west-northwest while funneled in the flow between the Atlantic surface ridge to the north and inverted surface trough to materialize to the west. At 120 hours an upper trough sliding eastward across the US/Canada border region is expected to team up with the cut-off upper trough over the southeastern United States to expand on the ridge weakness being created by the inverted surface trough... therefore an increase in the north angle of Fiona's westward track is anticipated during that timeframe. My updated forecast track is unchanged and keeps the center of Fiona just north of the northeastern Caribbean Islands. Also noting the NHC official forecast as of this writing is shifting north toward this idea.
Regarding forecast intensity... the short-term strength of Fiona is threatened by a chunk of the upper vorticity tied to Earl's remnant system... which will soon become cut-off and sent southwestward toward Fiona by an upper ridge to amplify in the western Atlantic (the amplification of the upper ridge is expected due to the warm sector of a strong eastern Canada/northwest Atlantic frontal system now materializing with the support of the above-mentioned eastern North America upper trough). With the thunderstorm activity remaining lopsided to the east side of the circulation... Fiona is already showing signs of being sheared by this upper vorticity. By studying the upper wind pattern in the 1800Z GFS model run from this evening... I do not anticipate at this time the shear will be strong enough to weaken the tropical storm through 48 hours. At 72 hours it appears likely the tropical storm will escape the upper vorticity and slide underneath a lower shear and upper outflow environment directly below the western Atlantic upper ridge... and I project only a little strengthening during that timeframe as the intensity forecast soon after becomes uncertain due to a couple of variables. One of them is how much land interaction Fiona will have with the Dominican Republic and Haiti (Hispaniola) landmass. The second variable is how much wind shear Fiona will be experiencing. In the higher shear scenario... some of the current Caribbean upper vorticity gets sent northeastward into Fiona by the cut-off southeastern US upper trough... with the shear continuing as the cut-off upper trough itself approaches Fiona in a lower amplitude state. In the lower shear scenario... the Caribbean upper vorticity which is already weakening while remaining cut-off from high-latitude cold air dissipates before getting a chance to shear Fiona... and the cut-off upper trough over the southeastern United States becomes more amplified as an adjacent upper ridge building over the United States becomes a little more amplified. The global model consensus tonight appears to be shifting toward the lower shear scenario and a higher longer range intensity for Fiona... therefore I no longer weaken Fiona below 60 mph maximum sustained winds at the conclusion of the 5-day forecast. This is also in agreement with the NHC intensity forecast as of this writing.
Regarding impact to land areas:
(1) I recommend interests in the northern Lesser Antilles... Virgin Islands... and Puerto Rico begin preparing for tropical storm conditions (gusty winds... heavy rains with flash flooding potential... and some coastal sea swells). The timeframe for impacts in this region is expected to be Friday and Saturday.
(2) I recommend that interests in the Dominican Republic and eastern Bahamas should be aware of Fiona due to longer range uncertainty in the intensity forecast. At this time it appears potential is increasing for tropical storm force conditions along the north coast of the Dominican Republic on Sunday... and eastern Bahamas for Monday.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0000Z Sep 15)...50 mph maximum sustained wind tropical storm centered at 16.7N-52W
IOH 24 Hr Forecast (0000Z Sep 16)...50 mph maximum sustained wind tropical storm centered east of the Lesser Antilles at 17.8N-57W
IOH 48 Hr Forecast (0000Z Sep 17)...50 mph maximum sustained wind tropical storm centered just north of the northern Lesser Antilles at 18.8N-62W
IOH 72 Hr Forecast (0000Z Sep 18)...60 mph maximum sustained wind tropical storm centered just north of Puerto Rico at 19.5N-66W
IOH 96 Hr Forecast (0000Z Sep 19)...60 mph maximum sustained wind tropical storm centered just offshore of the northern Dominican Republic coast at 20.5N-70W
IOH 120 Hr Forecast (0000Z Sep 20)...60 mph maximum sustained wind tropical storm centered over the eastern Bahamas at 22.5N-73W
AREA OF INTEREST #29...The eastern Atlantic tropical wave of low pressure that has been pulling westward and away from the Republic of Cabo Verde Islands has become less organized and as of this writing features only small amounts of thunderstorm activity well removed to the north. The tropical wave appears to be struggling due to competition for surface inflow with the sprawling tropical wave to the east... tagged as area of interest #30 on this blog. It appears development potential for this tropical wave has ended and now lies with the adjacent tropical wave mentioned in area of interest #30 which is becoming the dominant in the region. This is my planned final statement on this tropical wave as an area of interest on this blog.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Sep 16)...0% chance of tropical cyclone formation (eastern tropical Atlantic near 15.5N-36W)
AREA OF INTEREST #30...The tropical wave of low pressure that was over western Africa has recently entered the eastern tropical Atlantic. Its associated sprawling mass of thunderstorm activity has fizzled... however leaves behind a still-sprawling area of low clouds offshore of Africa with scattered showers and thunderstorms on the south side of the cloud mass. The low clouds suggest a broad area of rotation centered near 10.5N-17.5W which is a little further west of my previous forecast. Therefore the updated forecast track in this outlook is adjusted accordingly. Favoring this tropical wave as it moves across the eastern and central tropical Atlantic over the next five days is the persistent tropical upper ridge in the region featuring low shear and upper outflow. However I continue to cap peak odds of tropical cyclone formation at 20% due to the current lack of computer model support showing development. Also noting that I have lowered short term odds of tropical cyclone formation due to the recent reduction in the tropical wave's thunderstorm activity... and as the currently observed broad circulation will need some time to consolidate.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Sep 16)...0% chance of tropical cyclone formation (eastern tropical Atlantic near 11N-22W)
IOH 48 Hr Outlook (0000Z Sep 17)...5% chance of tropical cyclone formation (eastern tropical Atlantic near 11.5N-27W)
IOH 72 Hr Outlook (0000Z Sep 18)...15% chance of tropical cyclone formation (eastern tropical Atlantic near 12N-32W)
IOH 96 Hr Outlook (0000Z Sep 19)...20% chance of tropical cyclone formation (eastern tropical Atlantic near 12.5N-37W)
IOH 120 Hr Outlook (0000Z Sep 20)...20% chance of tropical cyclone formation (central tropical Atlantic near 13N-42W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z (Sep 14) CMC Model Run...
**For Tropical Storm Fiona... weakens to a tropical wave while moving across the northern Lesser Antilles... Virgin Islands... and Puerto Rico from 54 to 72 hours... remnant wave crosses the Dominican Republic and Haiti through 96 hours... tropical wave redevelops into a tropical low over eastern Cuba at 126 hours... regains tropical storm status on the north-central Cuban coast by 144 hours... reaches strong tropical storm strength while moving into the Florida Keys at 168 hours.
**For area of interest #29... No development shown
**For area of interest #30... tropical wave consolidates into a tropical low near 11.8N-31.5W at 132 hours... tropical low located near 14.5N-35W at 168 hours
1200Z (Sep 14) ECMWF Model Run...
**For Tropical Storm Fiona... weakens to a remnant low while moving across the northern Lesser Antilles... Virgin Islands... and Puerto Rico from 48 to 72 hours... re-gains tropical depression status in the norhtern edge of the Caribbean and just offshore of the southeast Dominican Republic coast at 96 hours... moves northwest across the eastern Dominican Republic through 120 hours... moves northwest across the eastern and central Bahamas as a strengthening compact tropical storm through 168 hours.
**For area of interest #29... tropical wave leaves behind a tropical low near 13.5N-47.5W at 120 hours... tropical low approaches the central Lesser Antilles by 168 hours
**For area of interest #30... no development shown
1800Z (Sep 14) GFS Model Run...
**For Tropical Storm Fiona... weakens to a remnant low while moving across the northern Lesser Antilles... Virgin Islands... and Puerto Rico from 63 to 93 hours... weakens further to a wave while passing over the Dominican Republic and Haiti through 123 hours... east side of remnant wave re-develops a surface low that swings north into the eastern Bahamas through 168 hours.
**For area of interest #29... no development shown
**For area of interest #30... no development shown
1800Z (Sep 14) NAVGEM Model Run...
**For Tropical Storm Fiona... reaches the northern Lesser Antilles at 66 hours as a strong tropical storm... reaches hurricane strength while passing just north of the Virgin Islands and Puerto Rico through 90 hours... as a potentially intense hurricane turns north and reaches 22.5N-68W at 120 hours
**For area of interest #29... no development shown
**For area of interest #30... no development shown