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Tropical Depression Eight Forecast Discussion Number 3

2020-07-23 16:50:23| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Thu Jul 23 2020 000 WTNT43 KNHC 231450 TCDAT3 Tropical Depression Eight Discussion Number 3 NWS National Hurricane Center Miami FL AL082020 1000 AM CDT Thu Jul 23 2020 Satellite imagery indicates that the depression is getting better organized, with a better-defined center located near the northeastern end of a broadly curved convective band. Satellite intensity estimates from TAFB and SAB have increased to 30 kt, and that will be the initial intensity for this advisory. An Air Force Reserve Hurricane Hunter aircraft is currently enroute to investigate the depression. The initial motion is west-northwestward or 285/8 kt. A mid-level ridge over the central United States is the predominant steering influence, and the global models forecast this ridge to build during the several days. This should cause the depression to turn more westward by 48-60 h and south of west after about 72 h. The track guidance is in good agreement with that scenario, and the new NHC forecast track, which has only minor adjustments from the previous track, lies near the various consensus models. The new forecast track has the center making landfall along the Texas coast between 48-60 h. The depression is in an environment of light shear and over warm sea surface temperatures, so at least slow strengthening is expected until landfall. The new intensity forecast, which lies a little below the intensity consensus, now calls for a peak intensity of 45 kt before landfall. Data from the Hurricane Hunter will give more details on whether the structure of the cyclone has improved or not, which will be incorporated into the next forecast cycle. Key Messages 1. The depression is expected to strengthen and it could bring tropical-storm-force winds to portions of the Texas coast, where a tropical storm watch is in effect. 2. The depression is expected to produce heavy rains along the Gulf Coast from Louisiana to the Lower Texas Coast. These rains could result in flash flooding and minor river flooding. FORECAST POSITIONS AND MAX WINDS INIT 23/1500Z 26.3N 90.7W 30 KT 35 MPH 12H 24/0000Z 26.7N 91.8W 30 KT 35 MPH 24H 24/1200Z 27.4N 93.4W 35 KT 40 MPH 36H 25/0000Z 27.8N 94.9W 40 KT 45 MPH 48H 25/1200Z 28.0N 96.5W 45 KT 50 MPH 60H 26/0000Z 28.0N 98.0W 40 KT 45 MPH...INLAND 72H 26/1200Z 27.9N 99.3W 30 KT 35 MPH...INLAND 96H 27/1200Z 27.5N 101.0W 20 KT 25 MPH...POST-TROP/INLAND 120H 28/1200Z 27.0N 103.0W 15 KT 15 MPH...POST-TROP/INLAND $$ Forecaster Beven

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Hurricane Douglas Forecast Discussion Number 13

2020-07-23 16:47:23| National Hurricane Center (East Pacific)

Issued at 500 AM HST Thu Jul 23 2020 000 WTPZ43 KNHC 231447 TCDEP3 Hurricane Douglas Discussion Number 13 NWS National Hurricane Center Miami FL EP082020 500 AM HST Thu Jul 23 2020 The intensity of Douglas has leveled off in the overnight hours with the eyewall convection weakening, but the eye temperatures becoming a lot warmer, suggesting that the system has become a little more steady state. The wind speed is kept at 105 kt, which nearly matches the latest CIMSS satellite consensus (SATCON). The cyclone has less than a day over warm water left to intensify before it encounters SSTs less than 26C. Douglas should only slowly weaken thereafter during the next few days due to the cooler waters along the predicted track since the vertical shear should remain low through Saturday. As the cyclone approaches the Hawaiian Islands on Sunday, while the SSTs increase, so does the shear, and thus a continued weakening is forecast. Model guidance is consistent from the last forecast, and no significant changes were made to the NHC wind speed prediction. Douglas has been moving a little faster to the west-northwest, or 290/17. 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. While the guidance remains in very good agreement, the only significant change to note is that this forecast is a bit faster than the previous one, but not as fast as the ECMWF or its ensemble mean. 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. FORECAST POSITIONS AND MAX WINDS INIT 23/1500Z 13.6N 135.9W 105 KT 120 MPH 12H 24/0000Z 14.5N 138.3W 110 KT 125 MPH 24H 24/1200Z 15.8N 141.5W 105 KT 120 MPH 36H 25/0000Z 17.0N 144.6W 95 KT 110 MPH 48H 25/1200Z 18.1N 147.7W 85 KT 100 MPH 60H 26/0000Z 19.1N 150.6W 75 KT 85 MPH 72H 26/1200Z 19.8N 153.5W 65 KT 75 MPH 96H 27/1200Z 20.7N 159.1W 55 KT 65 MPH 120H 28/1200Z 21.5N 165.5W 45 KT 50 MPH $$ Forecaster Blake

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Tropical Storm Gonzalo Forecast Discussion Number 8

2020-07-23 16:45:20| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Thu Jul 23 2020 000 WTNT42 KNHC 231445 TCDAT2 Tropical Storm Gonzalo Discussion Number 8 NWS National Hurricane Center Miami FL AL072020 1100 AM AST Thu Jul 23 2020 Recently-obtained GCOM and WindSat microwave data from overnight shows that Gonzalo's center is a little farther south than previously estimated. In addition, the storm's structure has become a little disheveled since yesterday, with the deep convection losing some organization. SAB's data-T number responded to this by falling to 2.5, but overall the CI numbers and SATCON support maintaining 55 kt for now. There is still an incredible amount of uncertainty in Gonzalo's intensity forecast. Sea surface temperatures to the east of the Windward Islands are warm--close to 29C--and the storm is likely to be moving through an environment of relatively light shear at least for the next 48 hours or so. The ambient environment is not particularly moist, however, with mid-level relative humidity generally around 50 percent, and it already appears that this dry air is affecting Gonzalo. Small cyclones like Gonzalo tend to succumb to any type of adverse environmental conditions quite easily, and it's possible that the system could struggle during the next couple of days. This is the solution shown by some of the global models, particularly the ECMWF and UKMET. On the other hand, the hurricane statistical and dynamical models, as well as the GFS, continue to show Gonzalo strengthening to a hurricane before it reaches the Windward Islands. Out of an abundance of caution, the official forecast continues to show Gonzalo becoming a hurricane in about 24 hours, but the uncertainty in this scenario cannot be stressed enough. There is a higher degree of certainty that Gonzalo would weaken once it moves over the eastern and central Caribbean Sea, where even the GFS shows it opening up into a wave. Even with the southward adjustment of the initial position, Gonzalo still appears to be moving westward, or 270/12 kt. The subtropical ridge to the north is forecast to push Gonzalo toward the west or west-northwest, with an increase in forward speed, for the entire 5-day forecast period. Much of the track uncertainty hinges on exactly how strong Gonzalo gets, with the stronger model representations showing the storm making more poleward process. Models such as the ECMWF and UKMET, which keep Gonzalo weak or open it up into a trough, are along the southern side of the guidance envelope. The updated NHC track forecast has been shifted southward some, to account for the new initial position and to be a little closer to the intensity consensus, HCCA, and the Florida State Superensemble. Key Messages 1. There is an increasing risk of wind and rain impacts from Gonzalo in portions of the southern Windward Islands this weekend, 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 conditions are possible across portions of the southern Windward Islands. Hurricane Watches are currently in effect for Barbados and St. Vincent and the Grenadines, and additional watches for other islands could be required later today. 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 23/1500Z 9.6N 48.3W 55 KT 65 MPH 12H 24/0000Z 9.8N 50.0W 60 KT 70 MPH 24H 24/1200Z 10.1N 52.7W 65 KT 75 MPH 36H 25/0000Z 10.5N 55.7W 70 KT 80 MPH 48H 25/1200Z 11.2N 59.0W 70 KT 80 MPH 60H 26/0000Z 11.9N 62.3W 70 KT 80 MPH 72H 26/1200Z 12.6N 65.4W 65 KT 75 MPH 96H 27/1200Z 14.0N 71.4W 50 KT 60 MPH 120H 28/1200Z 15.5N 77.5W 40 KT 45 MPH $$ Forecaster Berg

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Tropical Storm Gonzalo Forecast Discussion Number 7

2020-07-23 10:42:54| National Hurricane Center (Atlantic)

Issued at 500 AM AST Thu Jul 23 2020 000 WTNT42 KNHC 230842 TCDAT2 Tropical Storm Gonzalo Discussion Number 7 NWS National Hurricane Center Miami FL AL072020 500 AM AST Thu Jul 23 2020 A 0441 UTC ATMS/Soumi NPP microwave overpass revealed a well-developed banding feature wrapping into the center from the east semi-circle. Cloud tops have once again cooled near the surface center and subsequently, the Dvorak satellite intensity estimates from both TAFB and SAB have increased to T3.5 (55 kt). Accordingly, the initial intensity is raised to 55 kt for this advisory. No major changes were made to the intensity forecast and there still remains a relatively high degree of uncertainty beyond day 3 while the cyclone moves through the Caribbean Sea. Strengthening is forecast through 48 hours as Gonzalo approaches the Islands and the forecast is close to a blend of the HCCA intensity consensus, the IVCN multi-model guidance and the Decay SHIPS. Beyond mid-period, the forecast reflects a weakening trend in respect to the European models solution, but at much more gradual rate. It should also be noted that the small size of this system makes it susceptible to significant fluctuations in intensity, both upward and downward. The initial motion is estimated to be due west, or 270/10 kt. The forecast track philosophy remains unchanged. Gonzalo is moving within low to mid-level easterly steering flow produced by a subtropical ridge anchored to the north of the cyclone, and this high pressure should steer the storm generally westward at a faster forward speed for the next few days. After that time, a motion toward the west-northwest is expected. Two distinct model clusters with differing forecast track solutions persist. The European models along with the Canadian indicate a weak cyclone moving generally westward through the southern Windward Islands and dissipating in 5 days or less. The NCEP models, on the other hand, show a much stronger tropical cyclone with a west-northwestward to northwestward motion toward Hispaniola. The NHC forecast basically down the middle of these to model clusters and is very close to the TVCA consensus aid. Interests in the Windward Islands should continue to monitor the progress of this system. A Hurricane Watch is in effect for Barbados. Key Messages 1. There is an increasing risk of wind and rain impacts from Gonzalo in portions of the southern Windward Islands this weekend. Hurricane conditions are possible on Barbados where a hurricane watch has been issued. 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 23/0900Z 10.0N 47.0W 55 KT 65 MPH 12H 23/1800Z 10.1N 48.7W 65 KT 75 MPH 24H 24/0600Z 10.4N 51.1W 70 KT 80 MPH 36H 24/1800Z 10.9N 53.9W 75 KT 85 MPH 48H 25/0600Z 11.5N 57.0W 75 KT 85 MPH 60H 25/1800Z 12.2N 60.1W 70 KT 80 MPH 72H 26/0600Z 13.0N 63.1W 65 KT 75 MPH 96H 27/0600Z 14.8N 68.8W 50 KT 60 MPH 120H 28/0600Z 16.5N 74.5W 40 KT 45 MPH $$ Forecaster Roberts

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Hurricane Douglas Forecast Discussion Number 12

2020-07-23 10:42:54| National Hurricane Center (East Pacific)

Issued at 1100 PM HST Wed Jul 22 2020 000 WTPZ43 KNHC 230842 TCDEP3 Hurricane Douglas Discussion Number 12 NWS National Hurricane Center Miami FL EP082020 1100 PM HST Wed Jul 22 2020 Douglas has rapidly intensified since earlier today, with satellite images showing a ragged, but nearly clear eye surrounded by cold cloud tops of -70 C. There appears to be a little dry air intrusion across the northern portion of the circulation, which is limiting the amount of deep convection wrapping around that part of the eye. Both Dvorak intensity estimates from TAFB and SAB have increased to 5.5/100 kt, while the ADT and SATCON estimate averages have increased to 105 kt. Since the cyclone's appearance has improved slightly since these estimates arrived, the advisory initial intensity has been set at 105 kt, making Douglas a major hurricane. The environmental conditions supporting the rapid intensification appear at their best at this time as the cyclone is over SSTs of over 28 C, with low wind shear in a moist air mass. If the cyclone can fight off the dry air in the northern semicircle, some additional strengthening is possible, especially early Thursday. However, Douglas should be gradually moving into a less hospitable environment for strengthening over the next few days, and in 36 h the cyclone is forecast to cross the 26 C SST isotherm and into a region where the 500-700 mb relative humidity is less than 60 percent. Later on in the forecast period, wind shear is also expected to be on the increase. These factors should cause the cyclone to gradually weaken beginning Thursday night. Douglas is expected to be at or near hurricane intensity as it approaches the Hawaiian Islands on Sunday, and all interests there should monitor forecasts as they evolve over the next few days. The NHC forecast was adjusted higher in the first 12 h based on the initial intensity, and is very close to the previous forecast after that time. This intensity forecast closely follows the various consensus aids. The initial motion is west-northwest or 295/15. Douglas should continue on a general west-northwestward motion for the next few days, steered by a large mid-level ridge extending across much of the central and eastern North Pacific. The cyclone is then forecast to turn more toward the west late in the forecast period as it moves near the Hawaiian Islands. The track guidance is tightly clustered and the new NHC is little changed from the previous one. 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 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. FORECAST POSITIONS AND MAX WINDS INIT 23/0900Z 13.1N 134.0W 105 KT 120 MPH 12H 23/1800Z 14.0N 136.3W 110 KT 125 MPH 24H 24/0600Z 15.3N 139.5W 110 KT 125 MPH 36H 24/1800Z 16.5N 142.5W 105 KT 120 MPH 48H 25/0600Z 17.6N 145.5W 90 KT 105 MPH 60H 25/1800Z 18.6N 148.5W 80 KT 90 MPH 72H 26/0600Z 19.4N 151.4W 70 KT 80 MPH 96H 27/0600Z 20.5N 157.1W 55 KT 65 MPH 120H 28/0600Z 21.0N 163.7W 45 KT 50 MPH $$ Forecaster Latto

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