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BIRDSEYE VIEW POSTS

Since 2012 on the now retired Weather Underground blogs, I have been posting annotated "birdseye view" charts of the Atlantic basin, with a detailed explanation and forecasting that references the chart. From there you may know me as "NCHurricane2009." While I now do these "birdseye view" posts here, I will continue to do comments at Yale Climate Connections via Disqus where the former Weather Underground community has moved to. Feel free to reply to me there, at my Disqus feed at this link, or via e-mail at IOHurricanes@outlook.com 

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MY 2024 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #91

Writer's picture: NCHurricane2009NCHurricane2009

Updated: Sep 30, 2024

*******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.*********


...UPDATE...MONDAY SEPTEMBER 30 2024 12:45 PM EDT...

The completed list of southeastern United States wind reports associated with Helene is now available at birdseye view post #90A (https://www.infohurricanes.com/post/my-2024-atlantic-hurricane-season-birdseye-view-post-90a-special-update). In addition... the following events have occurred since the full update below from Saturday:

(1) In the open north Atlantic... after tropical cyclone Isaac previously was arcing more north in track while swung by the current northwest Atlantic deep-layer frontal low... the track has recently deviated more eastward while Isaac has been caught in the flow associated with the tail-end of the high-latitude upper trough that has dove southeast into Europe from Greenland. Decreasing sea-surface temps along the track caused Isaac to weaken from a hurricane to a top-end tropical storm on Sunday... and recently have caused Isaac to transition into a remnant non-tropical frontal cyclone centered near 45N-30W.

(2) As expected... Tropical Storm Joyce has recently weakened to a sheared tropical depression in the open central Atlantic.

(3) The eastern Atlantic tropical wave of low pressure... which was previously tagged as area of interest #35 on this post... proceeded to become a little better organized and became Tropical Depression Twelve by Sunday afternoon. While beginning to reach lower shear toward the core of the regional tropical upper ridge... the depression has become better organized and has recently briskly intensified into Tropical Storm Kirk with 50 mph maximum sustained winds.

(4) The tropical wave of low pressure that emerged from Africa behind what is now Kirk was quickly introduced into the NHC tropical weather outlook as of Sunday. The NHC has continuously increased its odds of tropical cyclone formation... and I will have an assessment on this new area of interest during my next full update on the Atlantic tropics.


...SATURDAY SEPTEMBER 28 2024 9:30 PM EDT...

Helene is now a fading remnant frontal low over the western Kentucky/Tennessee border region… see remnants of Helene section below for more info. See Hurricane Isaac and Tropical Storm Joyce sections below for more information on the current pair of open Atlantic tropical cyclones. In addition monitoring the following areas of interest:

(1) See area of interest #34 for a tropical wave of low pressure which could develop in a few days while approaching the western Caribbean and surrounding land areas.

(2) See area of interest #35 section below for the eastern tropical Atlantic wave of low pressure which has recently been upgraded to an area of interest.

(3) For the next African tropical wave of low pressure that emerges into the Atlantic behind area of interest (AOI) #35…  the outflow of AOI #35 will push the current upper vorticity near the NW Africa coast south toward the Atlantic tropics. Even though most models have stopped developing this wave… will watch to see if it shows signs of development under a highly-divergent low-latitude upper ridge that becomes defined in the relatively higher pressures south of the upper vorticity… and will upgrade the wave to another area of interest in future updates if necessary.


REMNANTS OF HELENE... Helene has transitioned to a weakening remnant surface frontal low while whirling west into the core of the regional upper vortex parked over the western Kentucky/Tennessee border region where supportive upper divergence is lacking… and accordingly is expected to dissipate over the the next day or so. Because Helene is no longer a tropical system… this is my final statement on this system on this blog.


TROPICAL STORM JOYCE... The organized tropical wave of low pressure in the central tropical Atlantic finally becomes Tropical Storm Joyce within the last 36 hours. The well-defined center that became upgraded to Joyce is northwest of the previous forecast… creating an early exposure to southwesterly wind shear present on the northwest side of the regional tropical upper ridge… and it is likely Joyce has already peaked in intensity as the shear is already pushing the thunderstorms toward the north side of the circulation. Previously was expecting Joyce to curve north around the west side of the east Atlantic surface ridge and into the deep-layer southwesterly flow ahead of the deep-layer mid-ocean ridge weakness that will be materializing between the merger of Isaac… the central Atlantic upper vorticity on top of Isaac… and the currently developing NW Atlantic deep-layer cyclone that Isaac will be interacting with. The more northwest position of the storm forces a westward adjustment of the forecast track which by 48+ hours places it in conflicting steering between the east Atlantic surface ridge and west Atlantic deep-layer ridge. The quasi-stationary position of Joyce in the updated forecast also places it in the south side instead of the southeast side of the deep-layer ridge weakness where the shear is more westerly and severe… thus the models…. NHC official forecast… and my updated forecast have Joyce weaken to a remnant low by 72 hours. Ex-Joyce will then be absorbed by a cold front to be driven by the NW Atlantic deep-layer cyclone and/or ex-Isaac… or alternatively drift south in a fujiwhara interaction with area of interest #35 and be absorbed by the NW quadrant of that area of interest.


Update as of 5 PM EDT… Joyce is slightly weaker with 45 mph maximum sustained winds.

******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********

0 Hr Position (1200Z Sep 28)… 50 mph maximum sustained wind tropical storm centered in the central tropical Atlantic at 20N-46W

IOH 24 Hr Forecast (1200Z Sep 29)… 45 mph maximum sustained wind tropical storm centered in the central Atlantic at 21N-50W

IOH 48 Hr Forecast (1200Z Sep 30)… 30 mph maximum sustained wind tropical depression centered in the central Atlantic at 22N-50W

IOH 72 Hr Forecast (1200Z Oct 1)… Remnant low centered in the central Atlantic at 22.5N-50W

*****National Hurricane Center (hurricanes.gov) official forecast as of 11 AM EDT*************************

3-Day Position (1200Z Oct 1)… 30 mph maximum sustained wind dissipating remnant low centered at 23.1-49.9W


HURRICANE ISAAC… While roaming eastward across the open North Atlantic… Isaac not only strengthened into a hurricane… it over-achieved while becoming a category 2. It is probable that while it was still over 26 deg C waters Isaac’s thunderstorms developed a boosting warm core upper outflow layer portioned below the 200 mb layer upper vorticity that had been previously holding back Isaac. Noting going forward Isaac will be heavily influenced by a developing deep-layer cyclone to its west that will be a merger between the surface frontal low emerging from Nova Scotia… its associated upper trough… and the aforementioned upper vorticity overhead of Isaac. Because the models have trended with Isaac being moreso captured by the deep-layer cyclone and less-so captured by the western tail end of the high-latitude upper trough now diving SE from Greenland… the long range track has shifted to being more north and less east and my updated forecast track shown below was adjusted accordingly. Although Isaac is currently over waters below 26 deg C… it is probable that developing upper divergence on the east side of the materializing deep-layer cyclone is helping Isaac keep its category 2 strength. Despite remaining under upper divergence through 48 hours… I expect decreasing water temps along the forecast track will allow for some weakening by 24 hours and loss of tropical characteristics by 48 hours. Noting thru 48 hours I have some east slant that remains in the north track as the tail of the high-latitude upper trough still appears close enough in the latest model runs to still drag Isaac. Beyond that time… the tail piece of the upper trough and what will be the non-tropical remnants of Isaac will most likely become absorbed by the northeast side of the deep-layer cyclone. Note over the next day or so swells generated by Isaac may reach the shores of the Azores.


Update as of 5 PM EDT… Isaac is slightly weaker with 100 mph maximum sustained winds.

******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********

0 Hr Position (1200Z Sep 28)... 105 mph maximum sustained wind hurricane centered in the northern Atlantic at 40.2N-39.7W

IOH 24 Hr Forecast (1200Z Sep 29)... 90 mph maximum sustained wind hurricane centered in the northern Atlantic at 42.5N-37.5W

IOH 48 Hr Forecast (1200Z Sep 30)... Hurricane-force remnant frontal cyclone centered in the northern Atlantic at 46N-36W

*****National Hurricane Center (hurricanes.gov) official forecast as of 11 AM

EDT*************************

5-Day Position (1200Z Oct 3)… 40 mph maximum sustained non-tropical frontal low centered in the far north Atlantic at 56.6N-25W


AREA OF INTEREST #34… A surface tropical wave of low pressure currently in the central Caribbean is currently positioned on the south side of the west Atlantic deep-layer ridge and in between a wave of upper vorticity to the southwest and another eastern Caribbean wave of upper vorticity to the southeast. As the older… less fresh wave of upper vorticity for the southwest dissipates from isolation from high-latitude cold air… split flow upper divergence over the surface wave may increase between the west side of the remainder southeastern upper-level wave and south side of the the deep-layer ridge… and I assess the surface wave has a low 10% chance of tropical cyclone formation through 48 hours while positioned between Jamaica and Central America. Through 72 hours I dip odds of development back down to 0% as the upper-level wave to the east directly rolls over the surface wave… then ramp development odds of the surface wave to 40% after that time as the passing upper-level wave then proceeds to collapse to the west of the surface wave from its isolation from high-latitude cold air which allows for an expanding upper anticyclone (low shear/outflow) to form in its wake and over the surface wave. There are also an increasing number of model runs that show development in the 3 to 5 day window in this manner… which is why I have increased my peak development odds to 40%.


Noting the forecast track for this area of interest is initially west around the aforementioned west Atlantic deep-layer ridge. Then after day 3 the track begins to bend northwest around the southwest edge of the ridge and due to its interaction with the east side of the collapsing second wave of upper vorticity. Other factors that will aid in the northwest track in the 3 to 5 day window include a steering surface low pressure field to the west extending into the Bay of Campeche and supported by divergence on the west side of the second wave of upper vorticity… and also the southwest side of a steering eastern US surface ridge that will be supported by the back convergent side of the next major North America upper trough (the next upper trough materializes from the merger between an amplified Central Canada upper trough and the upper vortex currently parked over ex-Helene).


Given the current outlook… interests across the Cayman Islands… northeastern Yucatan peninsula of Mexico… and western Cuba should watch for possible tropical cyclone impacts (gusty winds… heavy rainfall… and coastal surf) that could arrive by the middle of this upcoming week.

******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********

Formation chance through 2 days... 10% (between Jamaica and Central America near 15N-80W)

Formation chance days 2 to 3… 0% (offshore of the Nicaragua/Honduras border near 15N-82W)

Formation chance days 3 to 5… 40% (northeast corner of Yucatan peninsula near 21.5N-86.2W)

*****National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT*************************

Formation chance through 48 hours... 0%

Formation chance through 7 days... 50%


AREA OF INTEREST #35… The latest tropical wave of low pressure in the eastern tropical Atlantic was previously not forecast to develop in the models while it was expected for Joyce to dominate the surface inflow in the region. However the models have switched to developing this system as Joyce is now expected to dissipate in the short-term… and this is the 35th area of interest tracked on this site this year. While taking advantage of the outflow associated with the regional tropical upper ridge… thunderstorm activity has gradually increased in association with the wave… however the thunderstorms are lopsided to the south side of the maximum rotation to due to a combination of dry Saharan air to the north… plus northerly shear imparted by the east side of the upper ridge. Through day 3 however the tropical wave moves into lower shear at the core of the upper ridge… and I assign a peak 60% odds of tropical cyclone formation through that time due to the increased model support showing development. These are slightly lower than the NHC odds as of this writing as I prefer to see more organization before issuing higher odds. After day 3… this system track northwest toward the same central Atlantic ridge weakness that Joyce will be embedded within plus a western Atlantic ridge weakness to the generated by the next major upper trough to emerge from eastern North America (the next upper trough materializes from the merger between an amplified Central Canada upper trough and the upper vortex currently parked over ex-Helene). This system may experience southwesterly shear generated by the upper winds associated with the central Atlantic ridge weakness… and so I lower development odds to 50% for the day 3 to 5 window.

******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********

Formation chance through 3 days... 60% (eastern tropical Atlantic near 15N-40W)

Formation chance days 3 to 5… 50% (central tropical Atlantic near 19N-44W)

*****National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT*************************

Formation chance through 48 hours... 30%

Formation chance through 7 days... 70%


...COMPUTER MODEL SUMMARY...

Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/).


0000Z (Sep 28) CMC Model Run...

**For Hurricane Isaac... continues east-northeast then north through 78 hours while becoming pulled around northeast side of developing deep-layer cyclone…then proceeds to make a cyclonic loop SE of Greenland within the deep-layer cyclone (as a remnant non-tropical frontal cyclone) and becomes absorbed by a nearby competing center to the southeast within the deep-layer system by 132 hours

**For Tropical Storm Joyce... weakens to a quasi-stationary remnant low near 21.5N-50W at 78 hours… after absorbing area of interest #35 to the southeast the remnant low slowly drifts west to 22.5N-54W by 168 hours

**For area of interest #34... current central Caribbean tropical wave evolves into a broad tropical low over Central America... southeastern Mexico... and adjacent Caribbean and eastern Bay of Campeche waters through 84 hours... east end of broad tropical low develops into a better-defined center offshore of eastern Honduras through 108 hours… the better-defined center then becomes a tropical cyclone while moving NW into the western tip of Cuba through 132 hours… as a strengthening tropical cyclone proceeds NW into Gulf of Mexico waters offshore of SE Louisiana through 168 hours

**For area of interest #35… becomes absorbed by southeast side of ex-Joyce through 120 hours

**Additional tropical wave emerges from west coast of Africa at 72 hours… evolves into tropical low near 11.5N-34W by 126 hours… tropical cyclone formation suggested near 15.2N-38.8W through 168 hours


0000Z (Sep 28) ECMWF Model Run...

**For Hurricane Isaac... continues east-northeast then north through 96 hours while becoming pulled around northeast side of developing deep-layer cyclone… while slipping northeast toward Iceland (as a remnant non-tropical frontal cyclone) becomes absorbed by the deep-layer cyclone by 138 hours

**For Tropical Storm Joyce... weakens to a quasi-stationary remnant low near 21N-51W at 66 hours… remnant low then absorbed by west side of area of interest #35 through 96 hours

**For area of interest #34... current central Caribbean tropical wave evolves into a broad tropical low over Central America... southeastern Mexico... and adjacent Caribbean and eastern Bay of Campeche waters through 84 hours... Bay of Campeche portion of circulation becomes the dominant through 168 hours but without tropical cyclone formation

**For area of interest #35… large tropical cyclone formation suggested near 18N-45W at 126 hours… turns northwest and reaches 22.5N-50W by 168 hours as a large top-end tropical storm near hurricane strength


1200Z (Sep 28) GFS Model Run...

**For Hurricane Isaac... continues east-northeast then north through 69 hours while becoming pulled around northeast side of developing deep-layer cyclone… then proceeds to make a cyclonic loop SE of Greenland within the deep-layer cyclone (as a remnant non-tropical frontal cyclone) and becomes absorbed by a nearby competing center to the northeast within the deep-layer system by 129 hours

**For Tropical Storm Joyce… weakens to a quasi-stationary remnant low near 24N-49W at 63 hours… while continuing north-northeast merges with surface front driven by Isaac/deep-layer cyclone pair while located near  30.5N-46W through 102 hours… loses identity along front soon thereafter

**For area of interest #34... current central Caribbean tropical wave evolves into a broad tropical low over Central America... southeastern Mexico... and adjacent Caribbean and eastern Bay of Campeche waters through 60 hours... southeast end of broad tropical low rapidly develops into a tropical cyclone through 69 hours which moves NW offshore of Central America and moves into the NE corner of the Yucatan peninsula as a compact hurricane by 129 hours… the compact and potentially intense hurricane located in the Gulf of Mexico due south of Louisiana by 168 hours (note from 105 to 153 hours the remainder western Bay of Campeche portion of the broad tropical low becomes a second tropical cyclone which ultimately becomes absorbed by the west side of the dominant potentially intense hurricane)

**For area of interest #35… tropical cyclone formation suggested near 14.8N-37.5W at 27 hours… located near 24N-45W by 168 hours as a large and potentially intense hurricane


1200Z (Sep 28) NAVGEM Model Run...

**Not available at above-mentioned source

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