MED: 01M/APOLLO (NEARCHUS): ex-Tropical Storm

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MED: 01M/APOLLO (NEARCHUS): ex-Tropical Storm

#1 Postby Europa non è lontana » Mon Oct 25, 2021 1:10 am

A non-tropical low-pressure area in the central Mediterranean (as of 0600z, located ~70km W of Linosa), may gain some tropical characteristics soon. Most 00z global runs model the area losing its front and moving east in the short-term, with some models showing the system transitioning into a subtropical cyclone over the next few days (including GFS, ICON, ARPEGE, UKMET, ECWMF, GEM). Notably, models differ widely on landfall times and locations. While some models (inc. ICON, UKMET) show landfall in Calabria or Salento about 100 hours out, the GFS and GEM show landfall south of Benghazi, Libya, about 160 hours out. Intensity estimates also vary; the GFS is the strongest of the models, taking the system down to 983mb. ICON takes it down to 992mb, UKMet to 1004mb, before landfall.
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Re: Low pressure area in central Mediterranean

#2 Postby Vince_and_Grace_fan » Mon Oct 25, 2021 12:11 pm

The cyclone had subtropical appearance today as its well-defined center cut off from the decaying frontal zone, but the sustained and deeper convection was limited to a small area on the eastern side of the circulation. A morning ASCAT-B pass confirmed the well-defined center, and based on this the cyclone maybe a subtropical depression already. Lampedusa Island was in the middle of the circulation some hours earlier and the minimum pressure was 1008 hPa there.

According to the models the cyclone's center likely will became a bit more disorganized tomorrow, followed by a reorganisation on Wednesday/Thursday. However, the latest runs of GFS and ICON show a big shift to west in this process and thanks to this the cyclone will remain close to Sicily/Tunisia, much shorter time over water than the morning (00Z) runs expected, so it will be weaker too - the GFS now show a 35-40 kt TS over the Tyrrhenian Sea while the ICON a 40-45 kt, quite asymmetric TS near/over Sicily. The CMC still keeps on the Central Med. Sea development and stronger, 50-55 kt TS, while the Meteocenter WRF-NMM model also showed a similar strength, but it puts the cyclone near the coastline of Tunisia.

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Re: Low pressure area in central Mediterranean

#3 Postby Vince_and_Grace_fan » Mon Oct 25, 2021 4:11 pm

Small but persistent and deeper convective burst on the north-northeast edge of the center now, with some Cirrus-outflow.

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Re: Low pressure area in central Mediterranean

#4 Postby Europa non è lontana » Mon Oct 25, 2021 9:10 pm

The 18z ICON and GFS runs are in agreement over the system moving east, then northwest over Sicily, before emerging into the Tyrrhenian Sea. The system has a quite shallow but nonetheless warm-core. Cloud tops have been consistently peaking at or slightly above -50C for the past several hours.

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Re: Low pressure area in central Mediterranean

#5 Postby Europa non è lontana » Tue Oct 26, 2021 3:26 am

Update on 00z model runs. Most global models now show landfall on either Sicily or Calabria between 60 and 93 hours post-run, with intensity ranging between 1010-996mb. GFS 00z phase diagram shows shallow-warm core, and the system is non-frontal, but convection has waned overnight. The 00z GFS also shows a landfall over Malta on 00z Thursday, which may provide opportunities for land observations of a strengthening tropical storm in the Mediterranean, if the run verifies. The system is currently located about 170km SE of Luqa, Malta.
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Re: Subtropical Depression in the Central Mediterranean Sea

#6 Postby Europa non è lontana » Tue Oct 26, 2021 7:32 am

Latest ASCAT pass shows a well-defined circulation with max of 30kt winds. Sustained convection has been occurring for most of the past 18 hours, albeit limited to the northern side of the storm, with cloud tops consistently staying below -50C in some areas. The system is non-frontal and has a shallow warm core.

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Re: Subtropical Depression in the Central Mediterranean Sea

#7 Postby doomhaMwx » Tue Oct 26, 2021 10:28 am

A drifting buoy (WMO ID: 6102784) recorded a min SLP of 1005.4 mb near/in the center at 13Z today.

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Re: Subtropical Depression in the Central Mediterranean Sea

#8 Postby DanieleItalyRm » Tue Oct 26, 2021 10:31 am

Mm I think close tropical depression status now:

https://en.sat24.com/en/ly
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Re: Subtropical depression in central Mediterranean

#9 Postby Vince_and_Grace_fan » Tue Oct 26, 2021 11:48 am

Deep convective burst with cloud tops near/around -60 °C developed in the last 2 hours almost over the center. As Daniele told, the tropical transition maybe has already started. The overal structure of the cyclone also became more organized trough the day, however, the shear is also increasing from west (see qiuckly approaching Cirrus clouds from Tunisia on the last animation), and most of the models still show that the circulation likely will become a bit more disorganized tomorrow. But it is predicted that the shear will relax on Thursday, allowed strengthening.

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Re: Subtropical Depression in the Central Mediterranean Sea

#10 Postby doomhaMwx » Tue Oct 26, 2021 3:14 pm

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Re: Subtropical Depression in the Central Mediterranean Sea

#11 Postby Vince_and_Grace_fan » Tue Oct 26, 2021 4:15 pm

The shear tooks its toll, the convection weakened significantly and the center became fully exposed again.

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Re: Subtropical Depression in the Central Mediterranean Sea

#12 Postby Europa non è lontana » Wed Oct 27, 2021 12:25 am

Convection has diminished quite a lot over the night due to the shear and has been very limited, but conditions should allow convection to return tomorrow. 00z model runs have been overall quite interesting - the 00z GFS shows landfall over Messina at around 999mb 60h out, and the cyclone following the coast to a weaker secondary landfall near Napoli. The ICON shows a landfall over Catania at 998mb +60, then the cyclone stalling over Sicily, briefly moving over the Tyrrhenian Sea, and dissipation after moving back over Sicily. The Canadian, landfall over Catania at 997mb +60 and dissipation over Sicily. The UKMet is a big outlier, showing the cyclone moving over the Ionian Sea and stalling, intensifying to 990mb, before moving southeast and dissipating near Crete. ARPEGE has a landfall at 1004mb +90 in Benghazi.
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Re: Subtropical Storm in the Central Mediterranean Sea

#13 Postby Vince_and_Grace_fan » Wed Oct 27, 2021 2:18 am

A ship (call sign: A8YD3, position: 35.4N, 18.5E) reported 45 kt wind and 1010.0 hPa pressure on the northeast side of the cyclone at 02 UTC. The cyclone's center was near 34.5N, 18.1E at that time. This wind is likely at least partially associated with the gap wind effect between the Peloponnese and Creta (ASCAT measurements also showed this area of stronger winds in the last days, for example: https://manati.star.nesdis.noaa.gov/ascat_images/arch_25km_METB/AS2021298/zooms/WMBds158.png https://manati.star.nesdis.noaa.gov/ascat_images/arch_25km_METB/AS2021298/zooms/WMBas158.png ), but it suggested that the cyclone may reach tropical storm strength last evening, when the deep convection developed near the center.

First daylight visible satellite images show that the center is still well-organized.

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Re: Subtropical Storm in the Central Mediterranean Sea

#14 Postby Vince_and_Grace_fan » Wed Oct 27, 2021 8:23 am

The morning ASCAT passes (I put two together) confirmed that the circulation partially merged with the gap winds area and also with an elongated convergence zone across the Central Mediterranean Sea. The west side of this convergence is producing a larger area of deep convection right now with cloud tops between -55 and -65 °C, and this cluster may will merge with the original cyclone's center later (similarly as happened in the early development stage of Ianos last year).

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Re: Subtropical Storm in the Central Mediterranean Sea

#15 Postby Vince_and_Grace_fan » Wed Oct 27, 2021 11:13 am

On the 12Z ICON the cyclone remains east of Sicily and later turns to southeastward so it peaks much stronger than on the previous runs, and makes landfall in Libya. The ARPEGE also supports this scenario from the 00Z run.

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Re: Subtropical Storm in the Central Mediterranean Sea

#16 Postby Europa non è lontana » Wed Oct 27, 2021 1:08 pm

More models are going with the Libya solution this run than 00z. Canadian, ICON, ARPEGE. We should be concerned about intense rain and flooding in Libya if these verify, given that the Cyrenaica region rarely experiences significant rain events. GFS & Euro still show Messina landfall, UKMet has the system meander around the Ionian Sea.
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Re: Subtropical Storm in the Central Mediterranean Sea

#17 Postby Vince_and_Grace_fan » Wed Oct 27, 2021 1:32 pm

Europa non è lontana wrote:More models are going with the Libya solution this run than 00z. Canadian, ICON, ARPEGE. We should be concerned about intense rain and flooding in Libya if these verify, given that the Cyrenaica region rarely experiences significant rain events. GFS & Euro still show Messina landfall, UKMet has the system meander around the Ionian Sea.


It seems that GFS and ECM show a bit stronger (closed) sub-vortex west of the main cyclone tomorrow, and later they likely interact each other which result a bit faster northward forward speed by Friday, and both model predict that the cyclone center will be near/over the southeast coastline of Sicily at 12Z Friday. The other models show weaker subvortex, less interaction and they predict the center's position further south of the latitude of Sicily's southernmost tip.

For a compairson, here is the GFS vs. ICON and UKMet version:

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Re: Subtropical Storm in the Central Mediterranean Sea

#18 Postby Europa non è lontana » Wed Oct 27, 2021 6:21 pm

18z GFS now on board with landfall in Benghazi, although significantly weaker and later than the ICON 18z solution.

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Re: Subtropical Storm in the Central Mediterranean Sea

#19 Postby Nancy Smar » Wed Oct 27, 2021 9:39 pm

South of Italy, a warm-core subtropical storm has developed that is expected to move northward during the period, likely reaching southern Italy at Friday morning. Central Europe is affected by mid-level ridging, whereas a lifting trough enters western Europe.
South of Italy, the subtropical storm is expected to move northward. Models indicate that MLCAPE will increase to the east and south of this storm and clusters of thunderstorms are forecast, whereas weak lightning activity is likely close to the center, where CAPE is low. Main threat is extreme rainfall, also due to deep warm clouds within the south-easterly low-level flow that enters the storm. Additionally, tornadoes are not ruled out due to strong low-level vertical wind shear. The potential threat will likely continue on Friday.
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Re: Subtropical Storm in the Central Mediterranean Sea

#20 Postby Europa non è lontana » Thu Oct 28, 2021 1:19 am

00z model runs have further shifted towards a Libya landfall. ICON has landfall as a 988mb 115km/h (60kt) tropical storm +87. ARPEGE has landfall as a 995mb 85km/h (45kt) tropical storm +78. GFS, landfall as a 1005mb 75km/h (40kt) tropical storm +84. All of these models have landfall within 50km of Benghazi, Libya. The UKMet does not show the system making landfall, but instead meandering in the Ionian Sea and dissipating south of Crete. The Canadian has a weak 1010mb/55km/h (30kt) landfall near Ajdabiya. Probably the main hazard from this cyclone if the runs that show a Libya landfall verify will be very intense rain, which could cause flooding on an unprecedented scale.
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