*******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.**********
...SATURDAY JUNE 26 2021 10:16 PM EDT...
Satellite image as of 0150Z. Areas of interest circled in yellow are not mentioned in the NHC tropical weather outlook. Areas circled in a green dashed line are in the NHC 5-day tropical weather outlook. Areas circled in a solid green line are in the NHC 2-day tropical weather outlook:
NHC TAFB Surface Analysis 1200Z:
GFS Model Upper-Level Winds 1200Z:
See area of interest sections below for multiple areas being monitored for tropical development in the Atlantic basin. These areas of interest include:
(1) Area of interest #1...upper vortex and surface low in the vicinity of the Azores
(2) Area of interest #2...tropical wave of low pressure in the eastern tropical Atlantic
(3) Area of interest #3...surface trough of low pressure located north of the Caribbean Islands and supported by upper vorticity in the region…coastal Georgia could be affected by Monday evening…see area of interest #3 section below for details.
Elsewhere...what remains of a decaying upper trough and surface frontal system that was over the coastal SE US is a westward moving upper vortex sliding across the Gulf of Mexico. The eastern divergence zone of the upper vortex has been producing bands of thunderstorms…however this system has not been organized thus far as interestingly the surface trough of low pressure is on the south side of the upper vortex where the upper divergence is less…and where there is westerly shear and a lack of thunderstorm bands. Thus I have not declared a new area of interest here at this time. Meanwhile…upper winds in the Gulf of Mexico could become more conducive for development over the next 48 hours as a small upper ridge becomes established over the Gulf of Mexico…once the aforementioned upper vortex slides into Mexico and relatively higher pressures become established between that vortex and the upper vortex tied to area of interest #3. If the surface trough does take advantage of the small upper ridge’s outflow…if could become a tropical disturbance that moves northwest toward the Texas coast (while steered by the southwest side of the Atlantic surface ridge)…potentially bringing heavy rains Monday evening.
AREA OF INTEREST #1...An upper vortex and surface frontal low are currently centered just north of the western Azores near 40N-30W. The surface frontal low...which formed a couple of days ago under the supportive eastern divergent side of the upper vortex...has since whirled to a position directly below the upper vortex...essentially creating a deep-layered low pressure system. The surface frontal low which comprises the surface layer of the deep-layered circulation will no longer be able to strengthen as it is directly below the upper vortex center where there is a lack of divergence...and as shower and thunderstorm activity has not developed over the center as the upper vortex is not quiet cold enough to produce instability as the water temps at 40N latitude are barely in the low 20-deg C range.
While ingesting the northwest Atlantic upper trough that was nearing from the west…nothing much has happened at the surface as the CMC and ECMWF had predicted (those models predicted the remains of the upper trough would swing around the south side of the deep-layered circulation…and support a compact surface low with tropical characteristics with a small supportive divergence zone). Therefore subtropical development is no longer possible here…and this deep-layered circulation will drift uneventfully westward away from the Azores while steered in the short-term by the south side of the North Atlantic upper ridge. This is my final statement on this system on this blog.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Jun 27)...0% chance of subtropical cyclone formation (northeast Atlantic near 40.5N-35W)
AREA OF INTEREST #2...The vigorous tropical wave of low pressure in the eastern tropical Atlantic appears to have made some recovery in its battle with dry Saharan air located to the northwest. Long term (24 hour) satellite loops suggest the eastern thunderstorm bands of the tropical wave that were further away from the dry air were able to generate a broad low pressure spin that has thunderstorm banding in all quadrants of the circulation. Global models (except the NAVGEM) continue to not show development…which is likely why the NHC at one point lowered development odds to 10% in their outlook products. Probably due to the above-noted improved organization…at 2 PM EDT today the NHC bumped the odds to 30%. I support keeping my odds of development at 30% as the wave has not continued to get better organized since this morning…therefore it is not clear yet if the tropical wave will ultimately win in its battle with the dry Saharan air layer. Other than dry air…conditions for development are otherwise favorable due to warm waters along the forecast track (26+ deg C) and low shear and upper outflow beneath the tropical upper ridge in the region. Over the next five days…the tropical wave will continue west within the deep-layered easterly flow on the south sides of the Atlantic surface ridge and tropical upper ridge. Due to the current position of the tropical wave and latest model consensus…I have adjusted my forecast track points westward. However some of the models maybe moving the wave too fast to the west while assuming the wave weakens and de-amplifies from the dry air…and lower-amplitude waves in the atmosphere tend to move faster. Therefore I am still not as fast to the west as the model consensus until it is clear the wave won’t develop.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Jun 27)...5% chance of tropical cyclone formation (eastern tropical Atlantic near 11N-32.5W)
IOH 48 Hr Outlook (1800Z Jun 28)...15% chance of tropical cyclone formation (eastern tropical Atlantic near 11.5N-38W)
IOH 72 Hr Outlook (1800Z Jun 29)...30% chance of tropical cyclone formation (central tropical Atlantic near 12N-43.5W)
IOH 96 Hr Outlook (1800Z Jun 29)...30% chance of tropical cyclone formation (central tropical Atlantic near 12.5N-49W)
IOH 120Hr Outlook (1800Z Jun 30)…30% chance of tropical cyclone formation (east of the Lesser Antilles near 13N-54.5W)
AREA OF INTEREST #3...The following is a water vapor satellite image as of 0030Z in the environment of the western Atlantic surface trough of low pressure being monitored for tropical development (marked with a red-dashed line). The upper vortex above the surface trough has split into three smaller upper vortices L1 to L3. At the time of this satellite image…the surface trough is supported by split flow upper divergence between vortices L2 and L3:
The central Atlantic upper vortex located north of the Caribbean Islands has continued moving west into the western Atlantic while stretched and steered by the northwest Atlantic upper ridging currently in place. The upper vortex continues to support thunderstorms and a surface trough of low pressure. As the GFS model predicted yesterday…the cold core upper vortex as of today has split into multiple centers as it continues to weaken while cut-off from high latitude cold air…specifically the upper vortex now has three centers…marked L1 to L3 in the above satellite picture (these three centers are also marked in the GFS upper-level wind field in the Birdseye view chart…with three separate red Ls…at the beginning of this post if you look carefully). Initially I was confounded as to how the surface trough was directly below centers L2 and L3 and still getting upper divergence….I was waiting for L2 to dissipate and expecting the split flow upper divergence to commence in the gap between L1 and L3. However the above water vapor satellite image…which has a higher resolution than the GFS model upper-level wind plot…shows that there is enough space between L2 and L3 for split flow upper divergence to occur…and in fact this space is exactly where the surface trough of low pressure appears to be getting better organized tonight.
The northwest Atlantic upper ridging is forecast to push upper level vortices L2 and L3 westward toward the southeast US. Meanwhile…upper convergence to the north of L3 and southeast side of the northwest Atlantic upper ridging will keep the Atlantic surface ridge weighted to the west with no weakness...thus the surface trough will also be pushed west into the southeast US and remain in the favorable split flow upper divergence between L2 and L3. And given signs of a compact circulation with thunderstorm bands on satellite pictures…I give 50% odds of tropical cyclone formation for the surface trough for tomorrow and Monday. Interests along coastal Georgia should monitor this system carefully…heavy rainfall and gusty winds are possible Monday evening if indeed a tropical depression or tropical storm forms.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Jun 27)...50% chance of tropical cyclone formation (western Atlantic near 29.5N-74.5W)
IOH 48 Hr Outlook (1800Z Jun 28)...50% chance of tropical cyclone formation (offshore of Georgia near 30.5N-79.5W)
IOH 72 Hr Outlook (1800Z Jun 29)...0% chance of tropical cyclone formation (southwestern Georgia near 31.5N-84W)
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