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Tropical Storm Gonzalo Forecast Discussion Number 5

2020-07-22 22:32:11| National Hurricane Center (Atlantic)

Issued at 500 PM AST Wed Jul 22 2020 000 WTNT42 KNHC 222032 TCDAT2 Tropical Storm Gonzalo Discussion Number 5 NWS National Hurricane Center Miami FL AL072020 500 PM AST Wed Jul 22 2020 Satellite imagery suggests that Gonzalo's intensification has paused since the last advisory. The cyclone continues to show a central dense overcast, and microwave imagery indicates a small convective ring present under the overcast. However, the CDO has become a bit ragged, and the other banding seen earlier has dissipated. Subjective and objective satellite intensity estimates are in the 45-55 kt range, the the initial intensity remains a possibly conservative 45 kt. The initial motion is now 270/12. There is no change to the track forecast philosophy. Gonzalo is on the south side of a low- to mid-level subtropical ridge, and this feature should steer the storm generally westward at a faster forward speed for the next 60 h or so. After that time, a motion toward the west-northwest is expected. The new NHC forecast track is again little changed from the previous track, and it lies very close to the consensus models. The intensity forecast remains very problematic and of low confidence. On one side, the cyclone structure, light shear environment,and warm sea surface temperatures suggest strengthening, possibly even rapidly, should occur. In addition, the SHIPS-based guidance and the HWRF still make the system a hurricane. On the other side, the GFS, UKMET, and ECMWF models continue to forecast the system to weaken to an open wave by 120 h, possibly due to dry air entrainment and large-scale subsidence, and microwave imagery suggests that a tongue of drier air is present west and southwest of the cyclone. The NHC intensity forecast again compromises between these extremes, showing Gonzalo peaking as a hurricane in 36-48 h, followed by weakening in deference to the GFS/UKMET/ECMWF. The new intensity forecast is unchanged from the previous forecast. As noted before, the small size of this system makes it susceptible to significant fluctuations in intensity, both upward and downward. Interests in the Windward Islands should monitor the progress of this system, as watches could be issued sometime on Thursday. Key Messages 1. Gonzalo is expected to move near or over the southern Windward Islands this weekend, and could bring direct impacts from winds and heavy rainfall. While it is too soon to determine the magnitude and timing of those impacts, interests in the southern Windward Islands should monitor the progress of Gonzalo. FORECAST POSITIONS AND MAX WINDS INIT 22/2100Z 9.9N 45.0W 45 KT 50 MPH 12H 23/0600Z 10.0N 46.8W 55 KT 65 MPH 24H 23/1800Z 10.1N 49.2W 65 KT 75 MPH 36H 24/0600Z 10.3N 51.8W 70 KT 80 MPH 48H 24/1800Z 10.8N 54.6W 70 KT 80 MPH 60H 25/0600Z 11.3N 57.6W 65 KT 75 MPH 72H 25/1800Z 12.1N 60.8W 60 KT 70 MPH 96H 26/1800Z 14.0N 67.5W 50 KT 60 MPH 120H 27/1800Z 15.0N 72.5W 40 KT 45 MPH $$ Forecaster Beven

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Hurricane Douglas Forecast Discussion Number 9

2020-07-22 16:57:08| National Hurricane Center (East Pacific)

Issued at 500 AM HST Wed Jul 22 2020 000 WTPZ43 KNHC 221456 TCDEP3 Hurricane Douglas Discussion Number 9 NWS National Hurricane Center Miami FL EP082020 500 AM HST Wed Jul 22 2020 Douglas has resumed strengthening, after remaining steady state for almost 24 hours. The system has developed a ragged eye during the past couple of hours, although the cirrus from the inner-core convection has been obscuring that feature somewhat. There is a wide range among the satellite intensity estimates--between 55 kt and 77 kt--and the latest objective guidance is right at the hurricane threshold. Therefore, Douglas has been upgraded to a 65-kt hurricane, the first of the 2020 eastern Pacific season. During the period of reliable records, this is the 4th latest date on which the first hurricane of the season has formed. Douglas continues to move westward, or 265/13 kt, due south of a mid-level ridge which extends from the Baja California peninsula to 140W. This ridge is not expected to change much in strength or position in the coming days, and Douglas is therefore expected to move westward or west-northwestward, gradually gaining latitude, during the entire forecast period. There is very little spread among the track models, although the new suite of models is a little bit faster compared to the previous forecast. The updated NHC forecast has been adjusted accordingly, although it should be noted that the overall forecast path has changed very little. With Douglas's improved structure, low shear and warm sea surface temperatures (28-29C) should support further strengthening during the next 36 hours or so. There's still a significant chance of rapid intensification during that period, with the GFS- and ECWMF-based SHIPS RI guidance both over 50 percent. After that time, oceanic heat content values fall below zero along Douglas's forecast track, and it is likely that the hurricane would begin to gradually weaken, although not considerably so since vertical shear is not expected to increase until about day 4. SHIPS, HCCA, and the Florida State Superensemble are in very good agreement, especially during the first part of the forecast period, and so the NHC intensity forecast closely follows those solutions. This new forecast shows a slightly higher peak intensity compared to previous forecasts. 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. FORECAST POSITIONS AND MAX WINDS INIT 22/1500Z 11.8N 129.5W 65 KT 75 MPH 12H 23/0000Z 12.0N 131.4W 75 KT 85 MPH 24H 23/1200Z 13.1N 134.1W 85 KT 100 MPH 36H 24/0000Z 14.4N 137.0W 95 KT 110 MPH 48H 24/1200Z 15.7N 140.0W 90 KT 105 MPH 60H 25/0000Z 17.0N 143.0W 80 KT 90 MPH 72H 25/1200Z 18.0N 146.1W 70 KT 80 MPH 96H 26/1200Z 19.0N 152.0W 60 KT 70 MPH 120H 27/1200Z 20.0N 158.0W 50 KT 60 MPH $$ Forecaster Berg

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Tropical Storm Gonzalo Forecast Discussion Number 4

2020-07-22 16:39:33| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Wed Jul 22 2020 000 WTNT42 KNHC 221439 TCDAT2 Tropical Storm Gonzalo Discussion Number 4 NWS National Hurricane Center Miami FL AL072020 1100 AM AST Wed Jul 22 2020 Satellite imagery indicates that the cyclone has become significantly better organized since the last advisory. Visible imagery shows a well-defined central dense overcast with a hint of an eye and an outer convective band in the western semicircle, while a 09Z GMI microwave overpass showed a well-defined inner convective ring feature. Various subjective and objective satellite intensity estimates range from 35-55 kt, so the initial intensity is raised to a possibly conservative 45 kt. The initial motion is now 270/10. Gonzalo is on the south side of a low- to mid-level subtropical ridge, and this feature should steer the storm generally westward at a faster forward speed for the next 3 days or so. After that time, a motion toward the west-northwest is expected. The new NHC forecast track is little changed from the previous track, and it lies very close to the consensus models. The intensity forecast remains very problematic and of low confidence. On one side, the cyclone has been strengthening quickly and the good organization suggests additional, and possibly rapid, strengthening should occur. In addition, the SHIPS-based guidance and the HWRF make the system a hurricane and keep that intensity through 120 h. On the other side, the GFS, UKMET, ECMWF, and Canadian models are not big fans of this system, as they all forecast it to either be a weak low or dissipated by 120 h, possibly due to dry air entrainment and large-scale subsidence. The NHC intensity forecast again compromises between these extremes, showing Gonzalo peaking as a hurricane in 36-48 h, followed by weakening in deference to the global models. The new intensity forecast has significantly higher intensities than the previous forecast for most of the forecast period based on the recent intensification. As noted before, the small size of this system makes it susceptible to significant fluctuations in intensity, both upward and downward. Interests in the southern Windward Islands should monitor the progress of this system. Gonzalo is the earliest 7th named storm on record in the Atlantic basin, beating Gert of 2005 by 2 days. Key Messages 1. Gonzalo is expected to move near or over the southern Windward Islands this weekend, and could bring direct impacts from winds and heavy rainfall. While it is too soon to determine the magnitude and timing of those impacts, interests in the southern Windward Islands should monitor the progress of Gonzalo. FORECAST POSITIONS AND MAX WINDS INIT 22/1500Z 9.9N 43.6W 45 KT 50 MPH 12H 23/0000Z 10.0N 45.3W 55 KT 65 MPH 24H 23/1200Z 10.0N 47.7W 65 KT 75 MPH 36H 24/0000Z 10.1N 50.2W 70 KT 80 MPH 48H 24/1200Z 10.4N 52.8W 70 KT 80 MPH 60H 25/0000Z 10.7N 55.6W 65 KT 75 MPH 72H 25/1200Z 11.4N 58.8W 60 KT 70 MPH 96H 26/1200Z 13.0N 66.0W 50 KT 60 MPH 120H 27/1200Z 15.0N 71.5W 40 KT 45 MPH $$ Forecaster Beven

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Tropical Storm Douglas Forecast Discussion Number 8

2020-07-22 10:34:31| National Hurricane Center (East Pacific)

Issued at 1100 PM HST Tue Jul 21 2020 000 WTPZ43 KNHC 220834 TCDEP3 Tropical Storm Douglas Discussion Number 8 NWS National Hurricane Center Miami FL EP082020 1100 PM HST Tue Jul 21 2020 The overall appearance of Douglas has changed little over the past several hours. Satellite images show a continuation of dry air trying to be worked out of the eastern portion of the cyclone's circulation. The latest satellite intensity estimates from TAFB and SAB indicate that the initial advisory intensity remains 55 kt. The majority of intensity guidance continues to suggest that Douglas will soon overcome the dry air that has been holding the cyclone back from strengthening. And, the system is forecast to remain in a favorable environment for intensification for the next day or so. Beyond 36 h, the combination of cooler SSTs and dry air should cause Douglas to slowly weaken. The latest NHC forecast is a blend of the corrected consensus HCCA and the ICON and IVCN consensus aids. Based on this forecast, Douglas should become a hurricane sometime on Wednesday. Douglas is moving westward at around 13 kt. The ridge to the north of the cyclone is forecast to become oriented east-to-west while building westward over the next day or so. This should induce a gradual turn to the west-northwest along with a slight increase in forward speed. This general west-northwest motion is then forecast to continue through the remainder of the 5-day period. The model guidance has trended a bit faster throughout the forecast period, and the official forecast now lies in between the clustered consensus aids and the previous official forecast. FORECAST POSITIONS AND MAX WINDS INIT 22/0900Z 11.9N 128.0W 55 KT 65 MPH 12H 22/1800Z 12.0N 129.9W 65 KT 75 MPH 24H 23/0600Z 12.9N 132.4W 80 KT 90 MPH 36H 23/1800Z 14.1N 135.1W 90 KT 105 MPH 48H 24/0600Z 15.5N 137.9W 85 KT 100 MPH 60H 24/1800Z 16.7N 140.9W 80 KT 90 MPH 72H 25/0600Z 17.8N 143.9W 70 KT 80 MPH 96H 26/0600Z 19.1N 149.7W 60 KT 70 MPH 120H 27/0600Z 19.8N 155.3W 50 KT 60 MPH $$ Forecaster Latto

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Tropical Depression Seven Forecast Discussion Number 3

2020-07-22 10:33:00| National Hurricane Center (Atlantic)

Issued at 500 AM AST Wed Jul 22 2020 000 WTNT42 KNHC 220832 TCDAT2 Tropical Depression Seven Discussion Number 3 NWS National Hurricane Center Miami FL AL072020 500 AM AST Wed Jul 22 2020 The cyclone has become a little better organized this morning with indications of it developing convective banding features. Intensity estimates based on Dvorak classifications from TAFB and SAB are 30 kt and 35 kt respectively. I prefer to wait for consensus 35-kt estimates before naming the system, but it seems very likely that we will have Gonzalo over the tropical Atlantic very soon. The intensity forecast for this system is subject to more than the usual degree of uncertainty. Although the cyclone is likely to remain in an environment of fairly low shear, the influences of dry air and large-scale subsidence could inhibit strengthening in a few days. The NHC intensity forecast is similar to the previous one, and calls for some strengthening during the next couple of days followed by a leveling off thereafter. This is below the model consensus, but above the global model predictions which eventually dissipate the cyclone. 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 motion continues a little north of due west or 285/10 kt. A well-defined subtropical ridge is forecast to remain in place to the north of the tropical cyclone during the forecast period. The official forecast, like the previous one, is for a generally westward motion at a fast forward speed over the forecast periods. This is in close agreement with the latest dynamical model consensus. Interests in the southern Windward Islands should monitor the progress of this system. FORECAST POSITIONS AND MAX WINDS INIT 22/0900Z 10.0N 42.4W 30 KT 35 MPH 12H 22/1800Z 10.2N 44.1W 40 KT 45 MPH 24H 23/0600Z 10.2N 46.6W 45 KT 50 MPH 36H 23/1800Z 10.2N 49.0W 50 KT 60 MPH 48H 24/0600Z 10.4N 51.5W 55 KT 65 MPH 60H 24/1800Z 10.8N 54.2W 55 KT 65 MPH 72H 25/0600Z 11.3N 57.2W 55 KT 65 MPH 96H 26/0600Z 12.7N 64.4W 50 KT 60 MPH 120H 27/0600Z 15.0N 70.0W 45 KT 50 MPH $$ Forecaster Pasch

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