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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 

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*******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 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 dot gov) for the latest watches/warnings and official forecasts on active tropical cyclones.**********

...FRIDAY OCTOBER 25 2019 8:39 PM EDT...

See Tropical Storm Olga and Pablo sections below for all active tropical cyclones in the Atlantic basin. See the other area of interest sections below for additional areas being monitored for subtropical or tropical cyclone formation. Elsewhere...will be on the lookout in the next few days for a general increase in thunderstorms in the southern Gulf of Mexico and northern Yucatan peninsula beneath the low shear/upper outflow environment upper ridge axis in the region. Activity here could be boosted by a cold front to be driven into the area by the circulation of Olga. In addition...a tropical wave to the the central Caribbean Sea...interacted with the eastern divergence zone of an upper vortex along the cut-off upper trough that has been in the region to produce a large area of showers and thunderstorms today. As the cut-off upper trough continues to fade into upper vortices with lower wind shear...a tropical low pressure could also form from this activity and head westward toward the southern Gulf/northern Yucatan region too.

TROPICAL STORM OLGA...The tropical low pressure spin that has moved from the Bay of Campeche and into the western Gulf of quickly approaching Lousiana...has evolved into tropical depression seventeen and then Tropical Storm Olga in the last 24 hours. Olga is an unusual looking tropical storm while stretched north to south and embedded in a thick cloud band associated with a cold front nearing from the eastern United States. As such...Olga is expected to merge with the front and maintain strength as a frontal cyclone over the next 48 hours while maintained by the divergence zone of the front's upper trough. Therefore expect the frontal cyclone version of Olga to produce heavy flash flooding rain and gusty potentially damaging winds in the next couple of days from a long area stretching from Louisiana and Mississippi...through the Great Lakes region of North America...and into parts of southeastern Canada...see the special messages section at the top of the home page of this website for more details on the affected land areas and expected timing. By 72 hours...the remnant frontal cyclone of Olga and the supporting upper trough are expected to lose their identity in the much larger frontal cyclone and upper trough currently heading to the Hudson Bay region of Canada from western Canada. This updated forecast is a major change and completely different situation than I forecasted yesterday as I thought Olga would form and stay much further south while pinned by the suface ridge currently building to the west over the central United States. Instead...will watch to see if the cold front to be driven by the frontal cyclone version of Olga later develops thunderstorm activity in the southern Gulf of Mexico worth watching for tropical development in the low shear/upper outflow environment of the upper ridge axis to persist in the warm air ahead of Olga. At this time...not marking a southern Gulf area of interest in the above birdseye chart until we see thunderstorm activity develop first.

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

0 Hr Position (1800Z Oct 25)...40 mph maximum sustained wind tropical storm centered in the western Gulf of Mexico at 26.3N-93.2W

IOH 24 Hr Forecast (1800Z Oct 26)...40 mph maximum sustained frontal cyclone centered at the Arkansas/Missouri/Tennessee Border at 35.5N-89.8W

TROPICAL STORM PABLO...When the National Hurricane Center stated today that the frontal cyclone moving into the Azores was acquiring tropical was a bit puzzling to see what the hurricane center forecasters were on about until zooming in very close to the center of the cyclone. Indeed a peculiar small core of showers and thunderstorms is present and developed a banding-type eye feature as of 2100Z. I had to include a zoomed-in inset in the above birdseye chart so it is clearer to see the remarkably tiny tropical storm that Pablo is. This is also a remarkable event in that Pablo has managed to form in a tiny window of time that favors tropical the upper trough supporting the frontal cyclone that now effectively surrounds Pablo has reached maximum amplitude such that wind shear is low...and the formation of thunderstorms is due to the cold upper air temperatures of the upper trough despite the only mild water temps of 21 deg C. In previous discussion #165 and the special messages section of the home page of this site...I suggested that this system would not acquire tropical characteristics as wind shear would be too high while the overhead upper trough de-amplifies while absorbed into the much large upper trough of area of interest #1 (this is still expected to occur just after 24 hours)...and because the cold front of the developing storm in area of interest #1 would intrude from the west (this is still expected to occur between 72 and 96 hours from now). In other words...I though the narrow window of time that is present today for tropical development would be too narrow to allow for tropical development. Pablo can be thought of as a tiny chimney of spinning thunderstorms within the much larger frontal cyclone surrounding it...with its latent heat release producing a small warm core upper ridge with supporting outflow just beneath the much larger overhead upper trough. I forecast Pablo to still be a tropical storm in 24 hours as the chimney remains vertically stacked in a low shear environment as the latest GFS shows the overhead upper trough still having an amplified identity. But by 48 hours...wind shear should increase as the overhead upper trough loses its identity to the much larger upper trough of area of interest #1...which should throw the chimney out of vertical alignment...and not to mention the waters temps at the 48 hour forecat point are much colder such that thunderstorms should be diminished. A general northward swing in the current east track is expected while Pablo and surronding frontal cyclone are swing around the developing storm in area of interest #1...and my forecast track is where I assess the divergence maximum to be on the east side of the current overhead upper trough and absorbing upper troygh of area of interest #1. Gusty winds and high sea swells over the Azores were already expected for today regardless of whether Tropical Storm Pablo formed or not due to the existence of the larger frontal cyclone surrounding Pablo.

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

0 Hr Position (1800Z Oct 25)...45 mph maximum sustained wind tropical storm centered southwest of the Azores at 35.8N-32.2W

IOH 24 Hr Forecast (1800Z Oct 26)...45 mph maximum sustained tropical storm centered between Terceira and Sao Miguel of the Azores at 38N-26.2W

IOH 48 Hr Forecast (1800Z Oct 27)...Frontal cyclone centered north-northeast of the Azores at 43.5N-25W

AREA OF INTEREST #1...A surface cold front is currently pivoting eastward across the northwestern Atlantic waters southeast of Newfoundland while driven by a broad frontal low pressure and its upper trough located over eastern Canada. Computer models continue to agree a very large and intense frontal cyclone will form along this front over the next few days while settling at a location west of the Azores islands. The genesis of this storm is expected to be from an impressive upper divergence zone to form on the east side of the upper trough currently over eastern Canada as that trough later enters the northern Atlantic and amplifies into a rather impressive and large cut-off upper vortex. This will be in response to amplification of upper ridging over eastern Canada in the warm sector of a strong frontal cyclone forecast to be over the Hudson Bay region of central Canada during the forecast period. Forecast positions of this storm shown in the outlook below are based on the location of the divergence zone of the amplifying upper trough through 48 hours from this evening's 1800Z GFS model run...followed by an assumption that this system whirls into the center of the cut-off upper vortex from 72 to 120 hours (the GFS has the cut-off upper vortex center in the vicnity of 41N-35W by 120 hours). As forecast positions are adjusted a bit northeastward in repsonse to the latest evolution of the upper trough/cut-off upper vortex shown in the GFS...and I have moved up the time of possible subtropical cyclone formation 24 hours sooner to October 28 as the GFS shows the upper trough amplified into a cut-off upper vortex sooner. I have nudged upward my odds of subtropical cyclone formation from 10% to 20% as Tropical Storm Pablo is proof that the thermodynamic pattern of cold upper troughs/vorties in this region is enough to support tropical development despite mild water temperatures. But my odds remain only at 20% as the updated forecast track puts the center of this system over slightly cooler 20 deg C water. Regardless of acquisition of tropical characteristics or not...this storm is expected to bring large sea swells in the north-central Atlantic reaching the shores of the Azores islands...with the circulation possibly being large enough to deliver gusty winds to the islands in 3 to 4 days (72 to 96 hours) even while centered well west of the islands.

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

IOH 24 Hr Outlook (1800Z Oct 26)...0% chance of subtropical cyclone formation (northwestern Atlantic near 40N-51W)

IOH 48 Hr Outlook (1800Z Oct 27)...0% chance of subtropical cyclone formation (central Atlantic near 38N-41W)

IOH 72 Hr Outlook (1800Z Oct 28)...10% chance of subtropical cyclone formation (central Atlantic near 39N-37.5W)

IOH 96 Hr Outlook (1800Z Oct 29)...20% chance of subtropical cyclone formation (central Atlantic near 40.5N-35W)

IOH 120 Hr Outlook (1800Z Oct 30)...20% chance of subtropical cyclone formation (central Atlantic near 41N-35W)

AREA OF INTEREST #2...The tropical wave that recently emerged from Africa has seen a loss in thunderstorms depsite the favorable low shear and upper outflow environment of an upper ridge in the region. This is probably due to dry saharan air that lies just to the north. Therefore tropical cyclone formation here is no longer possible...this is my final statement on this tropical wave on this blog.

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

IOH 24 Hr Outlook (1200Z Oct 26)...0% chance of tropical cyclone formation (eastern tropical Atlantic near 28W)

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