This thread contains unofficial discussions on tropical cyclones in the 2023 season, with a focus on tropical cyclones in West Pacific, East Pacific and the North Atlantic basin. For official information, refer to the below links.

Generally, a new post will be made when a tropical or sub-tropical cyclone has or is expected to form within the next 24 hours and has the potential to affect major landmass.

Official information:

National Hurricane Center

Japan Meteorological Agency

Official agencies from other basins (RSMC)

A few useful links:

Tropical Tidbits

Weathernerds

CIMSS

RAMMB Real-Time Tropical Cyclone

Previous threads:

Before 2020 2020 2021 2022

One of the purposes of these topics is the provide an alternative source of information on these systems.

Unlike the information presented in the media, you will tend to find discussions related to the uncertainties of the forecasts, the range of possible outcomes (more adequately reflected in the ensembles I post rather than the "cone of uncertainty" which is based on historical records, and possible impacts and warnings.

The forecasts released here also tend to be earlier than the first official advisories because I will allow around 24 hours of lead time before a storm forms.

Subtropical Storm located a few hundred miles off the Mid-Atlantic coast

A well-defined area of low pressure continues to produce organized moderate convection, with cloud tops between -40 to -50C. Latest satellite image, as well as model data and ASCAT suggests that the occluded front, to which the low was previously attached to, is now separate from the center of the surface low. Peak scatterometer winds from a few hours ago were near 50 knots. These were located underneath the deepest convection. The same ASCAT image also revealed a compact system with a fairly small radius of maximum winds. Since the organisation of the low pressure area remains unchanged, the initial intensity of the cyclone is estimated at 50 knots, consistent with a Hebert-Poteat classication of ST3.0/45-50 knots.

Satellite-derived wind products from CIMSS shows the low pressure center is collocated with an upper level low. The upper low is providing marginal conditions to sustain thunderstorms activity (including moderate VWS and a relatively cold 300 mb temp of -50C that has offset low SST in the area (20-21C)).

Given the shallow warm core, interaction with the upper level low, and moderately deep convection near center, the cyclone is assessed as a subtropical (rather than a tropical) storm.

Global models show a short-term easterly track along the southern periphery of a large mid-level low in which the compact system is embedded. This is followed by a gradual turn to the north by 24 hours under the steering influence of a strengthening Atlantic ridge to the east. The subtropical storm is expected to make landfall over Atlantic Canada just beyond 24 hours and fill shortly after.

Marginal to unfavorable SST of near 20C will sustain thunderstorms activity. As the system gains latitude, along-track SST will decrease sharply to 16C and below, leading to rapid weakening prior to landfall.

Intensity forecast:

16/12z: 50 kt (Subtropical Storm)

17/00z: 50 kt

17/12z: 40 kt (Near Canada)

18/00z: 25 kt (Post-tropical/Inland)

Tropical Cyclone Freddy (13U/11S)

Tropical Cyclone Freddy originated from a tropical disturbance over Timor Sea, off the northwest coast of Australia, at the end of January. The disturbance was embedded within a monsoon trough and tracked westward across the Southern Indian Ocean over the next week or so and became a tropical cyclone on the 6th of February. Thereafter, environmental conditions were generally neutral to favorable and the tropical cyclone intensified significantly, partially due to favorable outflow aloft.

At 12 UTC today, the intensity of Freddy is estimated at 130 knots, based on Dvorak current intensity at T7.0/140kt, ADT and AiDT values near 125 knots and SATCON estimates at slightly over 120 knots. The cloud pattern is slightly asymmetrical and this is due to the effect of moderate 20-25 knots easterly VWS. The infrared eye has warmed over the past few hours, indicative of a weakening trend. SST in the area is near climatology at 27-28C. Upper level outflow remains robust, except in the eastern side of the system. Vapor imagery shows that Freddy is surrounded by drier mid-level air. Owing to its strong core, the circulation of Freddy appears well insulated from the effects of dry air entrainment. Latest microwave products do not indicate the presence of double eyewall structure.

Freddy remains steered by the subtropical ridge to the south. The subtropical ridge is forecast to strengthen and build toward the west, steering the tropical cyclone in a general westward direction over the next few days. While short-tern weakening is expected due to shear, the system could re-intensify slightly as it moves over warmer waters (28-29C) in Southwest Indian Ocean.

The ECMWF ensembles show high probability of direct impacts to at least part of Madagascar's coast, although this is expected to occur beyond 5 days. At this time, only a minority of GEFS members show re-curvature to the south before passing through the island. Given the strength of the steering ridge, a general westward track toward land is likely beyond Day 5, and Freddy could make landfall as an intense system.

Interestingly, the system has already accumulated 28 ACE. At this rate, it can easily surpass 50 ACE within the next 5 days, with a potential to exceed 65 ACE during its long lifetime.

Intensity forecast:

15/12z: 130 kt (Category 4)

16/12z: 125 kt

17/12z: 120 kt

18/12z: 130 kt

19/12z: 130 kt

20/12z: 130 kt

Tropical Cyclone Freddy

Light shear, moderate outflow and higher SST (now analysed at 28C) enabled the system to re-strengthen to 130 knots (equivalent to high-end Category 4). Current intensity is based on subjective current intensity number T6.5-7.0 and is higher than ADT and AiDT of 122-125 knots. The eye remains extremely distinct and the latest eye temperature analysed by ADT is still at 16.5C, though convection over the southern side is less vigorous. The cyclone is tracking west-southwestward along the mid-level steering ridge to the south.

The primary steering ridge will continue to build westward, enabling the cyclone to remain on a west-southwestward trajectory toward the east coast of Madagascar. Favorable upper level environment and warm (28-29C) along-track SST will sustain the current intensity of the storm over the next 24 hours.

Near landfall, easterly VWS will increase slightly and the cyclone should weaken as it tracks over warm waters. Rapid weakening will commence once the cyclone is over land.

Freddy will emerge into the Mozambique Channel as a much weaker system. A turn toward the west or west-northwest is expected due to the building of a secondary upper ridge to its southwest. A second landfall in South Africa is expected to occur shortly after 23/12z. High (28C) SST and moderate VWS and outflow may lead to slight intensification over the channel, if Freddy still possesses a tight circulation at this point.

Intensity forecast:

19/12z: 130 kt (Category 4)

20/12z: 130 kt

21/12z: 115 kt (Near the coast)

22/12z: 45 kt (TS)

23/12z: 55 kt

24/12z: 20 kt (Remnant Low)

Remnants of Freddy (11S)

Visible imagery around 12z depicts a defined circulation that is exposed to the west of vigorous convection. Strong upper level outflow as well as relatively high (28C east of 40E) SST is sustaining organized deep convection in the SE quadrant.

Maximum sustained wind is estimated at 25 knots, consistent with subjective Dvorak classifications between T1.0 to T1.5.

The system is tracking slowly southeastward along the southern periphery of a weak steering subtropical-ridge. Global models agree on slow consolidation over the next couple of days while tracking SE toward an area of higher (28C) SST. Mid-level humidity around the system is marginally conducive while expected VWS is light to moderate westerly. Strong poleward outflow and warm SST should lead to gradual intensification to a strong TS/weak hurricane.

Despite its latitude, global models develop a blocking high just to the south of its forecast track and will serve to impede eastward movement between Day 3 and Day 5 and thus the system should linger over the seas southwest of Madagascar. Higher shear and possible cold upwelling could limit further intensification.

Beyond Day 5, an approaching short-wave trough will weaken the block and the cyclone will potentially resume a more south to southeasterly track, although this is of low confidence.

Intensity forecast:

02/12z: 25 kt (TD)

03/12z: 30 kt

04/12z: 40 kt (TS)

05/12z: 50 kt

06/12z: 60 kt

07/12z: 60 kt

Get your surfboards lads we goin tornado/tsunami/whatever the fuck else surfin'

Tropical Cyclone Freddy (11S)

It is estimated that Tropical Cyclone Freddy intensified rapidly from 50 knots to 80 knots over the past 24 hours. A clear microwave eye was seen earlier and since about 08z, an infra-red eye has formed and persisted within the central dense overcast. The current intensity is based on a blend of objective and subjective satellite estimates, which gives a wide range intensities lying between 65 knots (AMSU) and 90 knots (Subjective T-number from JTWC and SSD) and is set to 80 knots. ADT is discounted at this time since it is giving an unrealistically low value.

Environmental conditions are favorable with low (5-10 knots) VWS and strong radial outflow. SST is at 28C. The most recent 37GHz imagery as well as model analysis do show significant dry air just to the west of the cyclone. Dry air entrainment might be the culprit of weakening eye and central convection. Freddy has been relatively slow moving during the past 12 hours, but a faster track toward the northwest is anticipated due to a strengthening ridge to its southwest.

Dynamic models show steady state or slight strengthening in the near term and thus only slight intensification is indicated in the next 24 hours. Beyond 24 hours, high SST and favorable outflow could cause dry air in the vicinity of the cyclone to mix out. The GFS model however, indicates a stronger relative shear due to faster southeasterly mid-level flow and minimal strengthening, while the HWRF is much more aggressive with its predicted intensity. The forecast intensity in this update more closely follow the GFS trend and cap the maximum intensity to just below Category 3 threshold. It should be noted that there is a chance for Freddy to become stronger than indicated.

Dry air import from stronger mid-level southerlies and land interaction will serve to weaken the storm gradually as it nears land. Both the deterministic GFS and ECMWF has the cyclone near the coast of South Africa at around 10/12z and landfall should occur near that time. Rapid weakening will occur over land and as Freddy does so, it will become more vertically shallow and be increasing influenced by a low level ridge across the South Pacific. The storm might slow down or come to a stall just inland as a result.

Intensity forecast:

07/12z: 80 kt (Category 1)

08/12z: 90 kt (Category 2)

09/12z: 95 kt

10/12z: 85 kt (Near the coast)

11/12z: 45 kt (TS/Inland)

12/12z: 30 kt (TD/Inland)

Tropical Cyclone Freddy (11S)

Satellite image suggests the system is fairly disorganized, with bursts of irregular cold overcast over the estimated LLC. This is likely due to some mid-level shear. Microwave imagery from approximately 07z shows curved band wrapping more than 75% around the mid-level center that was slightly offset to the north of the low level circulation. Satellite estimates around 12z lie between 55 to 75 kt. The intensity is set at 65 knots.

The cyclone is tracking slowly northwestward under competing steering flow from the building subtropical ridge to the south, and near equatorial ridge stretching southwestward from the Pacific and a slow westward to northwestward track is anticipated during the next couple of days. Global models have generally trended slower with its track over the past couple days and the system is expected to make landfall between 24 to 48 hours. The ECMWF takes the system further inland while the GFS and HWRF shows the system lingering near the coast of South Africa. This discrepancy is related to the difference in strength of the subtropical mid-level ridge to the south and the how the remnant circulation interacts with low-level northerly flow over the Pacific. This forecast is a compromise between the two scenarios, and leans more toward the more eastern solutions based on model trends and expected steering patterns.

Short-term environment is marginal for intensification, with the presence of mid-level shear and a lack of robust outflow being the most significant inhibiting factors. Models do show slight improvement in mid-level moisture prior to landfall and slight intensification is still possible.

After landfall, a slower-than-normal rate of weakening is forecast since part of the cyclone could still be over water, while the center lingers near the coast. An 180 turn in the long term toward the coast could occur as mid-level flow becomes westerly and there is a potential for the remnant low to emerge back over water. However, environmental conditions should be marginal due to moderate westerly shear. Confidence is extremely low.

Intensity forecast:

10/12z: 65 kt (Category 1/East of Mozambique)

11/12z: 65 kt (On the coast)

12/12z: 45 kt (TS)

13/12z: 30 kt (TD)

14/12z: 25 kt

15/12z: 35 kt (TS/Over Mozambique Channel)