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Hurricane Douglas Forecast Discussion Number 15

2020-07-24 04:44:03| National Hurricane Center (East Pacific)

Issued at 500 PM HST Thu Jul 23 2020 000 WTPZ43 KNHC 240243 TCDEP3 Hurricane Douglas Discussion Number 15 NWS National Hurricane Center Miami FL EP082020 500 PM HST Thu Jul 23 2020 Douglas remains a well organized hurricane in visible and infrared satellite imagery. The 15-nmi-wide eye remains very distinct and the surrounding cloud tops have cooled since the previous advisory. Although not evident in conventional satellite imagery, a recent AMSR-2 microwave satellite image showed evidence of concentric eyewalls. Subjective Dvorak T-numbers from TAFB and SAB are 6.0 (115 kt) and recent UW/CIMSS ADT estimates have been creeping upward, and now also close to T6.0. Based on these estimates, the initial wind speed has been raised to 115 kt, making Douglas a category 4 hurricane on the Saffir-Simpson Hurricane Wind Scale. Douglas has likely reached its peak intensity as it will be moving over cooler SSTs during the next day or so. Although the predicted track of the hurricane will bring it over warmer waters when Douglas approaches the Hawaiian Islands, vertical shear is forecast to increase at that time. This is expected to result in continued gradual weakening, however Douglas is forecast to be near hurricane strength when it moves close to Hawaii. Despite the slight increase in the initial intensity, the updated NHC wind speed forecast is unchanged from the previous advisory through 36 hours, and then follows the intensity consensus guidance thereafter. Douglas continues moving quickly west-northwestward or 295/16 kt. The hurricane is forecast to remain on this heading with some slight reduction in forward speed during the next day or so as it remains to the south of a large mid-level ridge. After that time, Douglas is forecast to turn westward to the south of another strong mid-level ridge the is predicted to build well north of the Hawaiian Islands later in the weekend. The new NHC track forecast is very similar to the previous advisory and lies just south of the various consensus aids out of respect of the ECMWF and its ensemble mean which lie along the southern edge of the track envelope. Key Messages: 1. Douglas is expected to move near or over portions of the Hawaiian Islands this weekend, and there is an increasing chance that strong winds, dangerous surf, and heavy rainfall could affect portions of the state beginning Saturday night or Sunday. Interests on the Hawaiian Islands should continue to monitor the progress of Douglas and the official forecasts as they evolve over the next few days. Watches could be issued on Friday. FORECAST POSITIONS AND MAX WINDS INIT 24/0300Z 14.9N 138.8W 115 KT 130 MPH 12H 24/1200Z 15.9N 141.2W 110 KT 125 MPH 24H 25/0000Z 17.1N 144.3W 100 KT 115 MPH 36H 25/1200Z 18.2N 147.4W 90 KT 105 MPH 48H 26/0000Z 19.2N 150.4W 75 KT 85 MPH 60H 26/1200Z 20.0N 153.2W 65 KT 75 MPH 72H 27/0000Z 20.5N 156.0W 60 KT 70 MPH 96H 28/0000Z 21.3N 161.8W 50 KT 60 MPH 120H 29/0000Z 21.8N 168.5W 45 KT 50 MPH $$ Forecaster Brown

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Tropical Storm Gonzalo Forecast Discussion Number 10

2020-07-24 04:40:41| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Thu Jul 23 2020 000 WTNT42 KNHC 240240 TCDAT2 Tropical Storm Gonzalo Discussion Number 10 NWS National Hurricane Center Miami FL AL072020 1100 PM AST Thu Jul 23 2020 After ingesting a hefty portion of dry high statically stable air this morning, Gonzalo appears to be on the comeback trail. Enhanced infrared BD-curve imagery shows that a small Central Dense Overcast with cloud tops of -80C is redeveloping over the surface center. A compromise of the available subjective and objective satellite intensity estimates supports maintaining 50 kt for this advisory. This morning's upper air sounding from Barbados revealed a very dry, high statically stable atmosphere with a mean RH of 23 percent and a CAPE of only 327 J/Kg. Consequently, Gonzalo will be moving into a rather harsh thermodynamic environment over the weekend. As a result, the NHC forecast calls for weakening beyond the 48 hour period as it enters the eastern Caribbean sea and dissipation well south of Hispaniola at day 5, or sooner as a few of the global models suggest. The intensity forecast is basically an update of the previous advisory through 48 hours, indicating a hurricane approaching and moving over the southern Windward Islands, and a faster weakening trend beyond day 2, similar to a consensus of the large-scale models. The initial motion is estimated to be westward, or 275/12 kt within the stiff mid-tropospheric steering flow provided by an anchored subtropical ridge to the cyclone's north. The song remains the same, with Gonzalo expected to speed up toward the west and west-northwest through the entire period. The NHC official forecast is based on a blend of the various consensus aids and is down the middle of the tightly clustered guidance. Key Messages 1. The risk of wind and rain impacts from Gonzalo in portions of the southern Windward Islands this weekend continues to increase, however there is significant uncertainty in how strong Gonzalo will be when it moves across the islands. 2. Despite the uncertainty in Gonzalo's future intensity, hurricane or tropical storm conditions are possible across portions of the southern Windward Islands Saturday and Saturday night. Hurricane and Tropical Storm Watches are currently in effect for some of the islands, and additional watches or warnings could be required tonight or early Friday. Interests in the southern Windward Islands should monitor the progress of Gonzalo and follow any advice given by local officials. FORECAST POSITIONS AND MAX WINDS INIT 24/0300Z 9.9N 50.6W 50 KT 60 MPH 12H 24/1200Z 10.2N 52.5W 55 KT 65 MPH 24H 25/0000Z 10.7N 55.1W 60 KT 70 MPH 36H 25/1200Z 11.5N 58.2W 65 KT 75 MPH 48H 26/0000Z 12.3N 61.3W 65 KT 75 MPH 60H 26/1200Z 13.3N 64.4W 55 KT 65 MPH 72H 27/0000Z 13.9N 67.3W 45 KT 50 MPH 96H 28/0000Z 14.4N 73.7W 35 KT 40 MPH 120H 29/0000Z...DISSIPATED $$ Forecaster Roberts

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Tropical Depression Eight Forecast Discussion Number 4

2020-07-23 22:47:27| National Hurricane Center (Atlantic)

Issued at 400 PM CDT Thu Jul 23 2020 000 WTNT43 KNHC 232047 TCDAT3 Tropical Depression Eight Discussion Number 4 NWS National Hurricane Center Miami FL AL082020 400 PM CDT Thu Jul 23 2020 Satellite imagery indicates that the depression continues to become better organized, with the center near the eastern edge of a large and broadly curved convective area, with a second curved band to the east. Several subjective and objective satellite intensity estimates have increased to 35 kt since the last advisory. However, surface observations, scatterometer data, and data from an earlier Air Force Reserve Hurricane Hunter mission show a large area of 25-30 kt winds south and east of the center, and no 35-kt winds to justify an upgrade at this time. Thus, the initial intensity remains 30 kt. A NOAA Hurricane Hunter aircraft is scheduled to investigate the depression this evening, and the current expectation is that they will find it is a tropical storm. The center meandered a bit today, possibly due to reformation. However, the system now seems to have resumed a west-northwestward motion of 285/7 kt. A mid-level ridge over the central United States is the predominant steering influence, and the global models forecast this ridge to build somewhat during the next several days. This should cause the depression to turn westward by 36-48 h and south of west after about 60 h. The track guidance remains in good agreement with that scenario, although there has been a slight southward shift in the guidance envelope and the consensus models. The new NHC forecast track is also shifted a little southward and has the center making landfall along the Texas coast in about 48 h. The depression is in an environment of light shear with good anticyclonic outflow, and it will be over warm sea surface temperatures until landfall. This should allow steady strengthening. The new NHC intensity forecast has been increased to show a peak intensity of 50 kt just before landfall, followed by steady weakening and eventually dissipation after landfall. The new intensity forecast is close to the intensity consensus. The aircraft and scatterometer data show that the strongest winds in the cyclone are currently occurring about 70-90 n mi from the center. This has caused the forecast wind radii to be expanded, and as a result a Tropical Storm Warning is needed for portions of the Texas coast. Key Messages 1. The depression is expected to strengthen and it is likely to bring tropical-storm-force winds to portions of the Texas coast, where a tropical storm warning has been issued. 2. The tropical cyclone is expected to produce heavy rains across portions of Louisiana, southern Texas, and northern Mexico. These rains could result in flash flooding and isolated minor-to-moderate river flooding. FORECAST POSITIONS AND MAX WINDS INIT 23/2100Z 26.1N 90.7W 30 KT 35 MPH 12H 24/0600Z 26.5N 91.9W 35 KT 40 MPH 24H 24/1800Z 27.1N 93.6W 45 KT 50 MPH 36H 25/0600Z 27.5N 95.3W 50 KT 60 MPH 48H 25/1800Z 27.6N 97.0W 50 KT 60 MPH 60H 26/0600Z 27.5N 98.5W 40 KT 45 MPH...INLAND 72H 26/1800Z 27.3N 100.0W 30 KT 35 MPH...INLAND 96H 27/1800Z 27.0N 102.0W 20 KT 25 MPH...POST-TROP/INLAND 120H 28/1800Z...DISSIPATED $$ Forecaster Beven

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Hurricane Douglas Forecast Discussion Number 14

2020-07-23 22:43:00| National Hurricane Center (East Pacific)

Issued at 1100 AM HST Thu Jul 23 2020 000 WTPZ43 KNHC 232042 TCDEP3 Hurricane Douglas Discussion Number 14 NWS National Hurricane Center Miami FL EP082020 1100 AM HST Thu Jul 23 2020 Visible satellite images show that Douglas is quite a powerful hurricane. The eye has become more crisp during the day, and infrared data also show that the eyewall convection has deepened. The initial wind speed is raised to 110 kt, which matches a blend of the latest TAFB/SAB Dvorak estimates. Douglas is beginning to move across the typical cool SST gradient of the eastern Pacific, implying that the hurricane is probably near its peak intensity. The cyclone should only slowly weaken on Friday and Saturday due to cooler waters along the predicted track and the vertical shear remaining low. As the hurricane approaches the Hawaiian Islands on Sunday, the SSTs increase but so does the shear. Since the shear generally dominates over marginally warm waters, a continued weakening is forecast. However, almost all of the guidance shows Douglas near hurricane strength as it moves close to Hawaii. The model guidance remains consistent, and no significant changes were made to the NHC wind speed prediction. Douglas continues moving fairly quickly toward the west-northwest. A large mid-level ridge over the eastern and central Pacific should continue to steer the hurricane on this general course and speed for the next couple of days, with some deceleration and a westward turn by late in the weekend. The guidance is a little more divergent than the previous cycle, with a subtle northward model trend at longer range due to a weaker ridge forecast north of Hawaii, though the ECMWF and its ensembles have shifted a little southward. Given these mixed signals in the guidance, very little change is made to the previous NHC track forecast, and the new official forecast lies on the southwest side of the model envelope. Key Messages: 1. Douglas is expected to move near or over portions of the Hawaiian Islands this weekend, and there is an increasing chance that strong winds, dangerous surf, and heavy rainfall could affect portions of the state beginning on Sunday. Interests on the Hawaiian Islands should continue to monitor the progress of Douglas and the official forecasts as they evolve over the next few days. Watches could be issued on Friday. FORECAST POSITIONS AND MAX WINDS INIT 23/2100Z 14.1N 137.3W 110 KT 125 MPH 12H 24/0600Z 15.0N 139.7W 110 KT 125 MPH 24H 24/1800Z 16.2N 142.8W 100 KT 115 MPH 36H 25/0600Z 17.4N 145.9W 90 KT 105 MPH 48H 25/1800Z 18.5N 149.0W 80 KT 90 MPH 60H 26/0600Z 19.4N 152.0W 70 KT 80 MPH 72H 26/1800Z 20.1N 154.9W 65 KT 75 MPH...NEAR HAWAII 96H 27/1800Z 21.0N 160.5W 55 KT 65 MPH 120H 28/1800Z 21.5N 167.0W 45 KT 50 MPH $$ Forecaster Blake

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Tropical Storm Gonzalo Forecast Discussion Number 9

2020-07-23 22:42:05| National Hurricane Center (Atlantic)

Issued at 500 PM AST Thu Jul 23 2020 000 WTNT42 KNHC 232041 TCDAT2 Tropical Storm Gonzalo Discussion Number 9 NWS National Hurricane Center Miami FL AL072020 500 PM AST Thu Jul 23 2020 Scatterometer data received just after the release of the previous advisory only showed winds of 40-45 kt, but given Gonzalo's small size, it's unlikely that the resolution of the instrument was able to capture the maximum winds. Even correcting for that, Gonzalo's winds were lowered to 50 kt on the 2 PM intermediate advisory, and that still looks good now with satellite intensity estimates ranging from 35 kt to 55 kt. Structure-wise, deep convection has redeveloped on top of Gonzalo's center, so the storm is not ready to give up its fight quite yet. There is still greater-than-normal uncertainty in Gonzalo's forecast intensity due to its small size and how it will behave in an environment of relatively light shear and warm sea surface temperatures counterbalanced by a lot of dry air. The statistical and dynamical hurricane models continue to show strengthening, while several of the global models, in particular the ECMWF and UKMET, still show Gonzalo weakening and opening up into a trough near or after it passes the Windward Islands. Based on the lower initial intensity and the latest guidance, the new official forecast has been lowered slightly, but it still brings Gonzalo to the hurricane threshold in 36-48 hours. Either way, Gonzalo's small size makes it susceptible to short-term changes in intensity that cannot be reflected in the official forecast. There is more confidence that weakening will occur after Gonzalo moves over the Caribbean Sea, with even the GFS showing the system becoming a trough. Given that, dissipation is now shown in the forecast at day 5. Gonzalo's initial motion is westward, or 275/11 kt. There has been no change in the track forecast reasoning, with Gonzalo expected to accelerate toward the west and west-northwest through the forecast period. The track guidance is fairly tightly clustered, showing Gonzalo's center crossing somewhere through the Windward Islands between 48-60 hours. Some of the models shifted northward a bit on this cycle, and the NHC track forecast has therefore been nudged in that direction close to the multi-model consensus aids, HCCA, and the Florida State Superensemble. However, users should not focus on these relatively small shifts in the forecast track from cycle to cycle, and for the Windward Islands in particular, consider that 48-60 hour forecast points can be off by an average of 60-80 nm. Key Messages 1. The risk of wind and rain impacts from Gonzalo in portions of the southern Windward Islands this weekend continues to increase, however there is significant uncertainty in how strong Gonzalo will be when it moves across the islands. 2. Despite the uncertainty in Gonzalo's future intensity, hurricane or tropical storm conditions are possible across portions of the southern Windward Islands Saturday and Saturday night. Hurricane and Tropical Storm Watches are currently in effect some of the islands, and additional watches or warnings could be required tonight or early Friday. Interests in the southern Windward Islands should monitor the progress of Gonzalo and follow any advice given by local officials. FORECAST POSITIONS AND MAX WINDS INIT 23/2100Z 9.8N 49.4W 50 KT 60 MPH 12H 24/0600Z 10.0N 51.2W 55 KT 65 MPH 24H 24/1800Z 10.5N 53.8W 60 KT 70 MPH 36H 25/0600Z 11.1N 56.6W 65 KT 75 MPH 48H 25/1800Z 12.0N 59.7W 65 KT 75 MPH 60H 26/0600Z 13.0N 62.6W 60 KT 70 MPH 72H 26/1800Z 13.8N 65.6W 55 KT 65 MPH 96H 27/1800Z 14.5N 72.0W 40 KT 45 MPH 120H 28/1800Z...DISSIPATED $$ Forecaster Berg

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