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Tropical Depression Seven Forecast Discussion Number 2

2020-07-22 04:36:24| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Tue Jul 21 2020 000 WTNT42 KNHC 220236 TCDAT2 Tropical Depression Seven Discussion Number 2 NWS National Hurricane Center Miami FL AL072020 1100 PM AST Tue Jul 21 2020 The depression remains quite small in size and its cloud pattern consists of a compact central dense overcast and some convective bands on its west side. The latest satellite intensity estimates and a recent ASCAT pass support maintaining the initial intensity at 30 kt. The initial motion is west-northwestward at 8 kt. The track forecast appears fairly straightforward. A strengthening deep-layer subtropical ridge to the north of the depression should cause the system to accelerate some toward the west or west-northwest during the next several days. This steering pattern should take the cyclone across the eastern Caribbean Islands and into the Caribbean Sea this weekend. The models are in fairly good agreement and there is high confidence in the track forecast. The intensity forecast is much trickier. The models continue to differ on the evolution of the depression, with the statistical-dynamical models and some of the hurricane regional models showing the system becoming a hurricane within the next few days. Conversely, the global models show little change in strength and even dissipate the system as it moves across the eastern Caribbean Sea. The global models seem to indicate that a combination of the cyclone's fast forward speed and associated shear, and dry air entrainment should prevent strengthening or lead to weakening. Given the large amount of uncertainty, only small changes were made to the previous prediction. This forecast lies a little below the consensus models giving slightly more weight to the global model solutions. It should be noted that small systems like Tropical Depression Seven are often difficult to predict as they are more likely to fluctuate in strength compared to larger cyclones. FORECAST POSITIONS AND MAX WINDS INIT 22/0300Z 10.0N 41.3W 30 KT 35 MPH 12H 22/1200Z 10.2N 42.7W 35 KT 40 MPH 24H 23/0000Z 10.3N 45.0W 45 KT 50 MPH 36H 23/1200Z 10.4N 47.5W 50 KT 60 MPH 48H 24/0000Z 10.5N 50.1W 55 KT 65 MPH 60H 24/1200Z 10.8N 52.9W 55 KT 65 MPH 72H 25/0000Z 11.3N 56.0W 55 KT 65 MPH 96H 26/0000Z 12.4N 63.1W 50 KT 60 MPH 120H 27/0000Z 13.7N 70.7W 45 KT 50 MPH $$ Forecaster Cangialosi

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Tropical Storm Douglas Forecast Discussion Number 7

2020-07-22 04:33:27| National Hurricane Center (East Pacific)

Issued at 500 PM HST Tue Jul 21 2020 000 WTPZ43 KNHC 220233 TCDEP3 Tropical Storm Douglas Discussion Number 7 NWS National Hurricane Center Miami FL EP082020 500 PM HST Tue Jul 21 2020 This afternoon's satellite presentation reveals a tropical cyclone that's struggling with the inhibiting factors from mid-level dry air intrusion. Cloud tops near the center of circulation have warmed considerably during the past few hours, and the primary convective band in the east semicircle has become a bit fragmented. A blend of an earlier SATCON of 52 kt, an ADT objective estimate of 51 kt and a Dvorak satellite classification of T3.5 from both TAFB and SAB supports holding the initial intensity at 55 kt, although the aforementioned recent changes in the cloud pattern may consider this as a bit generous. The better performing HFIP HCCA and IVCN multi-model intensity guidance still show Douglas shaking off the dry air invasion and strengthening into a hurricane in 12 hours, and the official forecast reflects this. The consensus intensity models and the FV3/GFS SHIPS show the cyclone reaching a peak intensity in around two days. Afterward, Douglas will be moving over 25-deg-C oceanic temperatures and into stable air mass. These negative contributions should, therefore, induce a slow weakening trend through day 5. The initial motion is estimated to be westward, or 270/12 kt within the mid-tropospheric easterly steering flow provided by a subtropical ridge anchored to the north of Douglas. This ridge is forecast to gradually build westward in response to a retreating large cut-off low near the Hawaiian Islands. As a result, Douglas should progressively turn West-northwestward by late Wednesday. and this general motion is forecast to continue for the remainder of the 5-day forecast period. The official NHC forecast is quite similar to the previous one with only a slight adjustment to the right beyond 72 hours through 120 hours in order to conform to the various consensus models. FORECAST POSITIONS AND MAX WINDS INIT 22/0300Z 12.1N 126.7W 55 KT 65 MPH 12H 22/1200Z 12.1N 128.5W 70 KT 80 MPH 24H 23/0000Z 12.6N 130.8W 80 KT 90 MPH 36H 23/1200Z 13.6N 133.2W 85 KT 100 MPH 48H 24/0000Z 15.1N 136.0W 90 KT 105 MPH 60H 24/1200Z 16.4N 138.8W 80 KT 90 MPH 72H 25/0000Z 17.5N 141.7W 70 KT 80 MPH 96H 26/0000Z 18.8N 147.3W 60 KT 70 MPH 120H 27/0000Z 19.4N 153.1W 50 KT 60 MPH $$ Forecaster Roberts

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Tropical Storm Douglas Forecast Discussion Number 6

2020-07-21 22:37:50| National Hurricane Center (East Pacific)

Issued at 1100 AM HST Tue Jul 21 2020 000 WTPZ43 KNHC 212037 TCDEP3 Tropical Storm Douglas Discussion Number 6 NWS National Hurricane Center Miami FL EP082020 1100 AM HST Tue Jul 21 2020 Douglas appears to have been trying to scour out a little bit of dry air on its western side during the day, although recent visible images suggest that deep convection is attempting to wrap entirely around the center. Because the convective pattern didn't change much from earlier, Dvorak classifications from TAFB and SAB remain T3.5/55 kt, so the initial intensity is held steady on this advisory. Strong ridging to the north of Douglas continues to impart a west-southwestward motion of the cyclone, or 255/13 kt. As mentioned this morning, the ridge is likely to take on a more east-west orientation as a mid-/upper-level low northeast of the Hawaiian Islands retrogrades westward, and this pattern evolution will allow Douglas to turn westward by tonight and then west-northwestward by late Wednesday. That general motion is forecast to continue for the remainder of the 5-day forecast period. The track guidance still showcases a faster ECMWF and slower GFS and HWRF solutions, and the overall envelope and model consensus aids have again nudged northward. The updated track forecast is therefore a little north of the previous one, mainly after 48 hours through day 5. Once deep convection can isolate Douglas's center from the ambient environment, low shear and warm sea surface temperatures of 28-29 degrees Celsius should allow intensification to resume. Despite this morning's hiatus in strengthening, the SHIPS Rapid Intensification (RI) guidance continues to key in on a significant chance of RI during the next day or two. Therefore, the intensity forecast from this morning has been left unchanged, and it still generally lies between the HCCA and Florida State Superensemble, closer to the higher end of the guidance envelope. Douglas should reach its peak intensity in about 48 hours, after which time oceanic heat content values drop to zero, which should cause some gradual weakening. Based on a partial ASCAT-A pass, Douglas's tropical-storm-force wind radii were increased on the northern side. FORECAST POSITIONS AND MAX WINDS INIT 21/2100Z 12.1N 125.4W 55 KT 65 MPH 12H 22/0600Z 11.9N 127.1W 70 KT 80 MPH 24H 22/1800Z 12.1N 129.5W 80 KT 90 MPH 36H 23/0600Z 13.0N 131.9W 85 KT 100 MPH 48H 23/1800Z 14.4N 134.5W 90 KT 105 MPH 60H 24/0600Z 15.7N 137.3W 85 KT 100 MPH 72H 24/1800Z 16.9N 140.2W 75 KT 85 MPH 96H 25/1800Z 18.5N 146.0W 65 KT 75 MPH 120H 26/1800Z 19.0N 151.5W 55 KT 65 MPH $$ Forecaster Berg

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Tropical Depression Seven Forecast Discussion Number 1

2020-07-21 22:36:48| National Hurricane Center (Atlantic)

Issued at 500 PM AST Tue Jul 21 2020 000 WTNT42 KNHC 212036 TCDAT2 Tropical Depression Seven Discussion Number 1 NWS National Hurricane Center Miami FL AL072020 500 PM AST Tue Jul 21 2020 Satellite imagery and scatterometer data indicate that the low pressure area located over the central tropical Atlantic has a well-defined circulation and sufficient organized convection to be designated a tropical depression. Thus, advisories are being initiated on Tropical Depression Seven. The initial intensity is set at 30 kt in best agreement with the subjective satellite intensity estimate from TAFB. The initial motion is 300/7. The depression is south of a strong subtropical ridge over the central Atlantic, and over the next several days it should turn generally westward and accelerate as it encounters the easterly flow associated with the ridge. The ECMWF, GFS, and UKMET models are in reasonably good agreement on their track forecasts, and the NHC official forecast is close to them and the various consensus models. The intensity forecast is lower confidence. The GFS, ECMWF, and UKMET models forecast the cyclone to be dissipated or be a weak low by the 120 h point, likely due to to some vertical shear and dry air entrainment. On the other hand, the SHIPS-based guidance and the HWRF forecast the system to be a hurricane at 120 h, shrugging off the shear and dry air. The NHC intensity forecast will be a compromise between these extremes, showing a peak intensity of 55 kt in 60-72 h followed by some weakening based on the global models. The cyclone is small in size, and as a result it could change intensity - both up and down - faster than what is currently forecast. FORECAST POSITIONS AND MAX WINDS INIT 21/2100Z 9.8N 40.4W 30 KT 35 MPH 12H 22/0600Z 10.1N 41.7W 35 KT 40 MPH 24H 22/1800Z 10.3N 43.9W 40 KT 45 MPH 36H 23/0600Z 10.3N 46.3W 45 KT 50 MPH 48H 23/1800Z 10.4N 49.0W 50 KT 60 MPH 60H 24/0600Z 10.6N 51.6W 55 KT 65 MPH 72H 24/1800Z 11.0N 54.7W 55 KT 65 MPH 96H 25/1800Z 12.0N 61.0W 50 KT 60 MPH 120H 26/1800Z 13.5N 68.5W 45 KT 50 MPH $$ Forecaster Beven

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Post-Tropical Cyclone Seven-E Forecast Discussion Number 6

2020-07-21 16:38:46| Tropical Depression LIDIA

Issued at 800 AM PDT Tue Jul 21 2020

Tags: number discussion forecast cyclone

 

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