*******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 OCTOBER 9 2023 1:30 PM EDT...
For the eastern Atlantic Ocean... continuing to watch a deep-layer cyclone northwest of the Azores that could acquire tropical characteristics in the days ahead... see area of interest #43 section below for more details. See area of interest #44 section below for information on a tropical wave of low pressure in the eastern tropical Atlantic that remains well-organized and is at high risk of tropical cyclone formation... as well as area of interest #45 section below for an additional tropical wave of low pressure that has become better defined and has just emerged from the west coast of Africa. Due to increased potential for a fujiwhara interaction between both waves... the potential for area of interest #44 to turn northwestward into the open central Atlantic over the next five days is reduced.
For the central Atlantic Ocean... a portion of the eastern North America upper vortex is forecast to eject into the mid-latitudes of the central Atlantic as an upper trough over the next few days where its eastern divergence zone will generate a frontal low pressure area. Even though sea-surface temperatures in the region are 24 deg C... below the typical 26 deg C threshold needed for tropical development... the boosting divergence zone of the upper trough could transition the forecast central Atlantic frontal low pressure area into a more tropical system with core thunderstorms as suggested by some recent model runs. However models disagree on the amplitude of the upper trough... with some runs showing a lower-amplitude upper trough more entangled with the remainder of the eastern North America upper vortex such that upper divergence is lower and wind shear unfavorable to tropical development is higher. Therefore not adding a tropical area of interest for the open central Atlantic in this update cycle.
For the Gulf of Mexico... a tropical disturbance has developed early and in the Bay of Campeche and therefore may develop before shear later increases across the Gulf. The primary impact from this system will be heavy rainfall across parts of the US Gulf coastal region as this system transitions into an elongating non-tropical frontal low pressure area in the northern Gulf of Mexico by Thursday... see area of interest #46 section below for more details.
AREA OF INTEREST #43... A deep-layer cyclone persists northwest of the Azores consisting of a surface frontal cyclone stacked below its parent upper vortex. Over the last 24 hours this system has drifted southwestward into warmer 20 to 22 deg C waters under the influence of an upper ridge to the west... and combined with rather cold de-stabilizing temps associated with the upper vortex (200 mb heights less than 1200 dekameters) the surface layer of the cyclone has seen an increase in shower and thunderstorms bands near its center. Therefore continuing to monitor this system for acquistion of tropical characteristics. Over the next 48 hours... an upper trough fragment now over Greenland will skip over the north side of the adjacent upper ridge and drag the deep-layer cyclone eastward. Even though this upper trough fragment leaves behind the deep-layer cyclone at 48 hours... the deep-layer cyclone is forecast to turn northeastward after 48 hours as a second high-latitude upper trough digs in from Greenland. Noting the 1200Z surface position of the deep-layer cyclone is a little northeast of my previous forecast... however only adjusting the forecast track eastward as the model consensus still shows the cyclone getting as far south as at least 42.5N latitude.
Regarding odds of subtropical cyclone formation... I have slightly raised peak odds to 40% due to the increase in shower and thunderstorm bands noted in the prior paragraph. Noting the surface layer of the cyclone is continuing to decay due to a lack of divergence at the core of the overhead upper vortex... therefore after 24 hours I begin to trim down development odds from the peak. By 96 hours the upper-layer of the cyclone will have merged with the second high-latitude upper trough... with the merged upper trough leaving behind the surface layer of the cyclone and causing the surface cyclone's dissipation with its trailing western convergence zone. This is when I drop subtropical development odds to 0%.
Regardless of whether or not the deep-layer cyclone acquires tropical characteristics... the Azores can expect another 2 days of coastal surf after which time the surface layer of the cyclone decays sufficiently to bring an end to the surf.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Oct 10)... 40% chance of subtropical cyclone formation (northeast Atlantic near 42.5N-34W)
IOH 48 Hr Outlook (1200Z Oct 11)... 20% chance of subtropical cyclone formation (northeast Atlantic near 42.5N-30W)
IOH 72 Hr Outlook (1200Z Oct 12)... 10% chance of subtropical cyclone formation (northeast Atlantic near 43N-26.5W)
IOH 96 Hr Outlook (1200Z Oct 13)... 0% chance of subtropical cyclone formmation (northeast Atlantic near 45N-19.5W)
******National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT***************************
Not in the official outlook
AREA OF INTEREST #44... The tropical wave of low pressure in the eastern tropical Atlantic that continues to be closely watched for signs of tropical cyclone formation has remained well organized but has not quiet yet become a tropical cyclone. Satellite pictures show another tropical wave of low pressure just to the east... tagged as area of interest (AOI) #45 in this update... has emerged from the west coast of Africa overnight. It could be competition for surface inflow and upper outflow with AOI #45 has delayed the development of this tropical wave. However since most models continue to develop this wave... and this wave has another 24 hours underneath low shear and outflow associated with a tropical upper ridge in the region... still assuming this wave will at least become a tropical depression and therefore I am continuing a tropical cyclone formation forecast with a specific track and intensity projection as outlined below.
Regarding track... this system has begun to move faster to the west under the influence of an eastern Atlantic surface ridge that has materialized under the western convergence zone of a passing eastern Atlantic upper trough. The eastern Atlantic surface ridge will be continued as the outflow of this system converges with the outflow of the central Atlantic mid-latitude upper ridge. For the October 11+ timeframe... the previous forecast track showed a turn to the northwest due to (1) some energy from the current eastern North America upper vortex which shifts toward the central Atlantic and creates a central Atlantic surface ridge weakness that attracts this system... (2) the central Atlantic mid-latitude upper ridge remains strong enough to break off the south part of the upper vortex of AOI #43 into another eastern Atlantic upper trough... and assuming this system becomes strong/tall enough to couple with upper winds it would be dragged northwestward by this upper trough. For this update I have gone with a more delayed turn to the northwest... followed by a slower drift toward the northwest due to (1) a possible fujiwhara interaction with AOI #45 through 72 hours (after which time this system absorbs AOI #45)... and (2) this system has not yet become a tropical cyclone which reduces the probability it will become strong/tall enough to couple with the additional incoming eastern Atlantic upper trough. The slow northwest drift by day 5 is then a product of this system being further south and away from the central Atlantic surface ridge weakness which makes it more difficult for the weakness to attract this system.
Regarding intensity... I forecast this system to still dominate over AOI #45 and become a tropical depression by 24 hours while it remains aided by the favorable low shear and outflow below the regional tropical upper ridge. After that time this system begins to deal with increased southwesterly shear associated with the additional eastern Atlantic upper trough that materializes in the October 11+ timeframe... however the shear should still be light enough between 24 and 48 hours to allow for some strengthening into a possible tropical storm (however I do not show much strengthening as this system could be disrputed while competing with and then absorbing AOI #45). I show weakening back to a tropical depression by 72 hours as the shear worsens. Beyond that time the eastern Atlantic upper trough and its shear begins to decay from prolonged isolation from high-latitude cold air... thus I show recovery back to a possible tropical storm by 120 hours.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Oct 9)... Tropical low centered in the eastern tropical Atlantic at 8N-24.5W
IOH 24 Hr Forecast (1200Z Oct 10)... 35 mph maximum sustained wind tropical depression centered in the eastern tropical Atlantic at 9N-29.5W
IOH 48 Hr Forecast (1200Z Oct 11)... 45 mph maximum sustained wind tropical storm centered in the eastern tropical Atlantic at 10.5N-32.5W
IOH 72 Hr Forecast (1200Z Oct 12)... 35 mph maximum sustained wind tropical depression centered in the eastern tropical Atlantic at 12.5N-34W
IOH 96 Hr Forecast (1200Z Oct 13)... 35 mph maximum sustained wind tropical depression centered in the eastern tropical Atlantic at 13.5N-36.5W
IOH 120 Hr Forecast (1200Z Oct 14)... 40 mph maximum sustained wind tropical storm centered in the eastern tropical Atlantic at 15N-38.5W
******National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT***************************
Formation chance through 48 hours... 60%
Formation chance through 7 days... 80%
AREA OF INTEREST #45... Satellite pictures show an organizing tropical wave of low pressure has recently emerged from the west coast of Africa... with the curvature in the associated thunderstorm bands suggesting a center of rotation just offshore and near 7.5N-14W as of 1200Z. Because of its organization and position beneath a low shear and outflow environment associated a regional tropical upper ridge... I have introduced this tropical wave as an area of interest for tropical development... this marks the forty-fifth tropical Atlantic area of interest I have tracked on this site this year. Forecast track takes this wave steadily west-northwest around the steering eastern Atlantic surface ridge and toward the circulation of the adjacent tropical wave to the west tagged as area of interest (AOI) #44. Because of its close proximity to AOI #44... it will be in competition for surface inflow and upper outflow with the adjacent AOI. Current assumption is that AOI #44 is further along in its development and will win the competition... however for this system I have already assigned a peak 30% odds of tropical cyclone formation by 48 hours given how much this wave has organized so far. I end the outlook after 48 hours with 0% development odds as AOI #44 itself will be dealing with shear that will dislodge its thunderstorm canopy eastward and closer to this system. Therefore if this system has not developed by 48 hours... it should succumb to a burst of westerly shear induced by AOI #44's sheared-off thunderstorm canopy... followed by absorption into AOI #44.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Oct 10)... 20% chance of tropical cyclone formation (eastern tropical Atlantic near 8N-19W)
IOH 48 Hr Outlook (1200Z Oct 11)... 30% chance of tropical cyclone formation (eastern tropical Atlantic near 9N-24W)
IOH 72 Hr Outlook (1200Z Oct 12)... 0% chance of tropical cyclone formation (eastern tropical Atlantic near 10N-29W)
******National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT***************************
Not in the official outlook
AREA OF INTEREST #46... The sprawling upper vortex over eastern North America has driven a surface cold front southward across the Gulf of Mexico... with the tail end of the front positioned over the Bay of Campeche. The tail end of the front has already spun up into a tropical low pressure with increased thunderstorms while supported by the outflow of an upper ridge axis in the region... bringing an early start to the anticipated southwestern Gulf of Mexico region tropical disturbance. The early start is allowing for possible development in the current low shear and outflow environment... before the shear later increases out ahead of a large upper trough to approach from western North America. As such the NHC has declared an area of interest for the Bay of Campeche and southwestern Gulf of Mexico... this marks the forty-sixth tropical Atlantic area of interest tracked on this site this year.
This system will be interacting with several features in the region including a US Gulf coast surface ridge... eastern Pacific tropical cyclones Lidia and Max... and a complex upper trough now moving into western North America featuring a southwest-to-northeast tilted leading piece of energy offshore of Baja Califonria and northwest-to-southeast tilted trailing piece of energy offshore of the northwestern US and Canada. Over the next 48 hours the US Gulf coast surface ridge pivots east and out of the way with the western convergence zone of a shortwave upper trough orbiting around the eastern North America upper vortex. At the same time Max is lifted northward into central Mexico by Lidia... and Lidia is also shoved northeastward toward central Mexico by the leading western North America upper trough energy. Therefore through 48 hours this system is expected to increasingly lift north in the southerly flow ahead of the Lidia-Max surface low pressure envelope and behind the departing US Gulf coast surface ridge. By 72 hours... while interacting with the elongated divergence zone ahead of the leading upper trough energy... this system is expected to become elongated and turn northeastward... transitioning into an elongated non-tropical frontal low pressure seperating the cold air associated with the leading upper trough energy and warm air ahead of the energy. There is uncertainty as to the position of this system in the 72+ hour window as some models even suggest the elongating non-tropical circulation splitting in half... with the eastern half zooming across the far southeastern US and western Atlantic as part of the leading upper trough energy becomes an eastward-zooming shortwave upper trough... and with the western half becoming another frontal low lifting northward into Louisiana and supported by the divergence zone of the trailing upper trough energy. In this scenario noting the western frontal low would eventually become absorbed inland over the US by a large frontal pressure arriving from western North America that is also supported by the trailing upper trough energy.
Regarding odds of tropical cyclone formation... I am inclined to go slightly higher than the 8 AM NHC outlook and assign a peak 30% odds of formation in the next 24 hours due to the amount of thunderstorms and rotation already seen with the initial tropical low pressure in the Bay of Campeche. By 48 hours conditions for development become difficult due to increasing westerly shear as the leading upper trough energy from western North America approaches... and also as surface pressures drop over a wide area as the Lidia-Max surface low pressure envelop approaches from central Mexico and due to the sprawling area of upper divergence to setup ahead of the leading upper trough energy. The enlargening area of low surface pressures increases the probability of this system losing its well-defined center needed for tropical cyclone formation and increases the probability of this system devolving into a broad system with multiple centers. As such I lower developemnt odds by 48 hours. The outlook is ended at 72 hours at the time this system is expected to transition into an elongating non-tropical frontal low pressure area as discussed in the prior paragraph.
The primary impact to land areas will be in the form of heavy rainfall for southeastern Louisiana... southern Mississippi... southern Alabama... southern Georgia... and southern Florida by Thursday as this system transitions into an elongating frontal low pressure area in the northern Gulf of Mexico.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Oct 10)... 30% chance of tropical cyclone formation (Bay of Campeche near 20N-94W)
IOH 48 Hr Outlook (1200Z Oct 11)... 10% chance of tropical cyclone formation (western Gulf of Mexico near 25N-94W)
IOH 72 Hr Outlook (1200Z Oct 12)... 0% chance of tropical cyclone formation (just offshore of southeastern Louisiana near 28.5N-90W)
******National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT***************************
Formation chance through 48 hours... 20%
Formation chance through 7 days... 20%
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields(http://moe.met.fsu.edu/tcgengifs/).
0000Z (Oct 9) CMC Model Run...
**For area of interest #43... frontal cyclone swings south in a cyclonic loop and reaches 41.5N-34.5W at 24 hours while potentially acquiring tropical characteristics... subsequently weakens to a frontal low that drifts east-northeast to 43N-25.5W through 108 hours where it then dissipates
**For area of interest #44... tropical cyclone formation suggested near 11N-35W at 66 hours... strengthening tropical cyclone curves north-northwest to 18.5N-39.5W through 120 hours
**For area of interest #45... no development shown for tropical wave currently just offshore of the west coast of Africa
**For area of interest #46... tropical low currently in southwestern Gulf of Mexico moves northwestward while merging with remnants of eastern Pacific Tropical Storm Max which results in a broad tropical low near 24N-97W at 72 hours... broad tropical low accelerates northeastward while becoming elongated and less tropical and makes landfall over the western Florida panhandle at 102 hours... as a non-tropical elongated frontal low continues east-northeast across southern Georgia and into the western Atlantic and reaches 31.5N-75W at 120 hours
**Through 54 hours upper trough energy that ejects into the central Atlantic from the eastern North America upper vortex produces a frontal low near 36N-54.5W... upper trough remains amplified enough while continuing east across central Atlantic such that frontal low intensifies into a frontal cyclone with potential core tropical characteristics through 120 hours near 35.5N-45.5W
0000Z (Oct 9) ECMWF Model Run...
**For area of interest #43... frontal cyclone swings south in a cyclonic loop and reaches 41.5N-34W at 24 hours while potentially acquiring tropical characteristics... subsequently weakens to a frontal low that drifts east-northeast to 42.5N-25.5W through 90 hours where it becomes absorbed by another new frontal low to the northeast
**For area of interest #44... tropical wave organizes into a tropical low near 15N-36.5W at 120 hours
**For area of interest #45... no development shown for tropical wave currently just offshore of the west coast of Africa
**For area of interest #46... tropical low currently in the southwestern Gulf of Mexico moves northwestward and becomes a larger/broader feature near 24N-97W at 54 hours... through 78 hours the tropical low becomes elongated and less tropical and splits into an eastern non-tropical frontal low that rapidly zooms east across north Florida and into the waters southeast of Bermuda throgh 120 hours and a western frontal low that drifts north into southeastern Louisiana through 120 hours
0600Z (Oct 9) GFS Model Run...
**For area of Interest #43... frontal cyclone swings south in a cyclonic loop and reaches 40.8N-34.5W at 24 hours while potentially acquiring tropical characteristics... frontal cyclone weakens to a frontal low while moving northeastward to 45N-26.5W through 63 hours... the weakening frontal low then undergoes a second cyclonic loop beneath its parent upper vortex and dissipates near 42.5N-29W at 96 hours.
**For area of interest #44... compact tropical cyclone formation suggested near 9N-26W at 30 hours... tropical cyclone moves... compact tropical cyclone moves northwest to 17N-44.5W through 120 hours without gaining much strength
**For area of interest #45... no development shown for tropical wave currently just offshore of the west coast of Africa
**For area of interest #46... tropical low currently in the southwestern Gulf of Mexico moves northwestward and becomes a larger/broader feature near 25N-97W at 45 hours... through 66 hours the tropical low becomes elongated and less tropical and splits into an eastern non-tropical frontal low that rapidly zooms east across north Florida and into the waters southeast of Bermuda throgh 120 hours and a western frontal low that drifts north into southeastern Louisiana through 108 hours which then loses its identity along cold front of additional frontal low that approaches from western and central North America.
0600Z (Oct 9) NAVGEM Model Run...
**For Area of Interest #43... frontal cyclone swings south in a cyclonic loop and reaches 41.2N-34W at 24 hours while potentially acquiring tropical characteristics... frontal cyclone weakens to a frontal low while moving northeastward to 44.5N-29W through 60 hours... the weakening frontal low then undergoes a second cyclonic loop beneath its parent upper vortex and dissipates just north of the Azores at 102 hours.
**For area of interest #44... tropical cyclone formation suggested near 11N-38.8W at 66 hours... strengthening tropical cyclone curves northwest and then northward to 17.5N-41.5W through 120 hours.
**For area of interest #45... no development shown for tropical wave currently just offshore of the west coast of Africa
**For area of interest #46... tropical low currently in the southwestern Gulf of Mexico moves northwestward and becomes a larger/broader feature near 22.5N-97W at 42 hours... makes landfall over southwestern Louisiana as a less tropical low pressure area at 84 hours and is absorbed by frontal low approaching from western and central North America shortly thereafter.