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Hurricane Fernanda Forecast Discussion Number 9

2017-07-14 04:37:43| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Thu Jul 13 2017 000 WTPZ41 KNHC 140237 TCDEP1 Hurricane Fernanda Discussion Number 9 NWS National Hurricane Center Miami FL EP062017 800 PM PDT Thu Jul 13 2017 Fernanda continues to strengthen. Although there has been no hint of an eye in geostationary satellite imagery, the center is embedded within a symmetric CDO and a recent SSMIS overpass revealed a small banded eye. The upper-level outflow is well established over the eastern and southern semicircles but there is some evidence of a little northerly shear beneath the high cirrus layer that may have temporarily slowed the intensification process. Subjective and objective Dvorak T-numbers range from T4.0 to T4.6, which yields an initial intensity estimate of 75 kt. The upper-level pattern over the cyclone is forecast to become ideal for strengthening with the shear remaining quite low throughout the forecast period. As a result, significant strengthening is forecast while the hurricane moves over SSTs of 28-29 deg C during the next couple of days. The SHIPS Rapid Intensification Index is still indicating a notable chance of RI over the next 24 hours, and the NHC foreast once again calls for rapid strengthening during the next 24 to 36 hours. After that time, eyewall replacement cycles could cause some fluctuations in intensity. In about 72 hours, the hurricane is expected to begin moving over cooler water which should result in weakening late in the period. Recent satellite fixes show that Fernanda is moving slightly south of west or 260/10 kt. A deep-layer ridge to the north of the cyclone is expected to keep the hurricane on a general westward heading during the next day or so. After that time, a mid- to upper-level trough to the northeast of the Hawaiian Islands is expected to cause the western portion of the ridge to weaken. This should cause Fernanda to turn west-northwestward over the weekend. The track guidance is in very good agreement, and the new NHC track is essentially an update of the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 14/0300Z 11.0N 117.0W 75 KT 85 MPH 12H 14/1200Z 10.9N 118.3W 90 KT 105 MPH 24H 15/0000Z 10.8N 120.2W 105 KT 120 MPH 36H 15/1200Z 11.1N 122.3W 115 KT 130 MPH 48H 16/0000Z 11.7N 124.6W 120 KT 140 MPH 72H 17/0000Z 13.0N 129.2W 120 KT 140 MPH 96H 18/0000Z 14.4N 133.2W 105 KT 120 MPH 120H 19/0000Z 15.8N 137.0W 85 KT 100 MPH $$ Forecaster Brown

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Hurricane Fernanda Forecast Discussion Number 8

2017-07-13 22:38:39| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Thu Jul 13 2017 000 WTPZ41 KNHC 132038 TCDEP1 Hurricane Fernanda Discussion Number 8 NWS National Hurricane Center Miami FL EP062017 200 PM PDT Thu Jul 13 2017 Fernanda is rapidly intensifying. Satellite imagery indicates that the central convection has become more symmetric, and there have been hints of an eye in visible imagery. In addition, earlier microwave imagery showed at lease a partial ring of convection around the center. Subjective and objective satellite intensity estimates range from 65-75 kt, so the initial intensity is increased to a possibly conservative 70 kt. Conservative or not, this is a 35 kt increase from this time yesterday. The initial motion is a little south of west or 260/10, with part of the southward component possibly due to some reformation of the center as the cyclone intensified. During the next 48 h, a deep-layer ridge to the north of Fernanda should steer the hurricane generally westward, and the new forecast is similar to the previous forecast. After that time, a large mid- to upper-level trough over the central Pacific north of Hawaii should cause the ridge to weaken, and the track guidance shows Fernanda turning west-northwestward in response. The guidance is forecasting a greater northward component of motion from 72-120 h than on the previous runs, and thus the latter part of the track forecast is nudged northward as well. Overall, the new forecast lies close to the various consensus models. While satellite imagery suggests that some shear continues to affect Fernanda, so far it has done little to slow the development. The hurricane should remain over warm water and in a light shear environment for the next 72 h, and the SHIPS model Rapid Intensification Index shows better than a 50 percent chance of a 35-kt increase in strength in the next 24 hours and a 45-kt increase in 36 h. Based on this, the intensity forecast calls for 36 h more of rapid strengthening. Given the lack of negative factors, except for the possibility of eyewall replacement cycles, the new intensity forecast could still be conservative even though it lies above the intensity guidance. After 72 h, Fernanda should encounter decreasing sea surface temperatures and drier air, and this is expected to cause a steady weakening. The new intensity forecast is again increased considerably over the previous forecast during the first 36 h, and it is decreased below for previous forecast at 120 h. FORECAST POSITIONS AND MAX WINDS INIT 13/2100Z 11.2N 116.0W 70 KT 80 MPH 12H 14/0600Z 11.1N 117.5W 85 KT 100 MPH 24H 14/1800Z 10.9N 119.4W 100 KT 115 MPH 36H 15/0600Z 10.9N 121.3W 115 KT 130 MPH 48H 15/1800Z 11.3N 123.5W 120 KT 140 MPH 72H 16/1800Z 12.5N 128.0W 125 KT 145 MPH 96H 17/1800Z 14.0N 132.5W 115 KT 130 MPH 120H 18/1800Z 15.5N 136.0W 95 KT 110 MPH $$ Forecaster Beven

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Tropical Storm Fernanda Forecast Discussion Number 7

2017-07-13 16:36:05| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Thu Jul 13 2017 000 WTPZ41 KNHC 131435 TCDEP1 Tropical Storm Fernanda Discussion Number 7 NWS National Hurricane Center Miami FL EP062017 800 AM PDT Thu Jul 13 2017 Recent IR and WV images show that Fernanda has begun to establish good outflow in all quadrants, indicating that the shear that previously affected the tropical storm is diminishing. Recent SSMI and SSMIS passes from 1016 and 1130 UTC, respectively, show that that convection is wrapping all the way around a mid-level center, but the low-level center remains displaced a little to the north-northeast. Dvorak estimates from TAFB and SAB have increased to T 3.5 / 55kt, and the initial intensity has been increased to that value. Confirming what the satellite data suggests, the analyzed shear has decreased below 10 kt. Warm SSTs and sufficient moisture are also contributing to an environment that is very conducive for continued intensification. The SHIPS-RII shows a greater than 50 percent chance of a 30 kt increase in 24 hours and a 45 kt increase in 48 hours. This is a notable increase in the probabilities which have doubled in the last 12 h. Considering the convective structure of the cyclone has improved over the past few hours, and the lack of any obvious inhibiting environmental factors, rapid intensification within the next 24 or 36 hours seems likely. The intensity forecast has been substantially increased for the first 48 hours and now explicitly shows an increase of 30 kt within 24 hours. Fernanda is forecast to be at or near major hurricane strength by tomorrow evening, with conditions favoring additional intensification after that. Near the end of the forecast period, the hurricane is expected to encounter decreasing sea surface temperatures that could cause slight weakening. The intensity forecast is near the top of the guidance envelope, close to the corrected consensus aids FSSE and HCCA. No major changes have been made to the track forecast. The initial motion estimate remains 265/9 kt. A deep-layer ridge extending over a large portion of the eastern north Pacific will steer Fernanda generally westward for the next 2-3 days. Most of the dynamical guidance still shows a slight weakening of the ridge after about 3 days which would cause Fernanda to turn toward the northwest. The NHC forecast is very close to to the track consensus TVCN and is nearly on top of the previous forecast. FORECAST POSITIONS AND MAX WINDS INIT 13/1500Z 11.7N 115.0W 55 KT 65 MPH 12H 14/0000Z 11.5N 116.4W 65 KT 75 MPH 24H 14/1200Z 11.2N 118.3W 85 KT 100 MPH 36H 15/0000Z 11.0N 120.3W 100 KT 115 MPH 48H 15/1200Z 11.2N 122.4W 110 KT 125 MPH 72H 16/1200Z 12.0N 126.9W 120 KT 140 MPH 96H 17/1200Z 13.4N 131.0W 115 KT 130 MPH 120H 18/1200Z 15.0N 135.5W 105 KT 120 MPH $$ Forecaster Zelinsky

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Tropical Storm Fernanda Forecast Discussion Number 6

2017-07-13 10:44:38| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Thu Jul 13 2017 000 WTPZ41 KNHC 130844 TCDEP1 Tropical Storm Fernanda Discussion Number 6 NWS National Hurricane Center Miami FL EP062017 300 AM MDT Thu Jul 13 2017 Fixes off of recent ASCAT data indicate that Fernanda's center is now fully embedded beneath the convective canopy, and cloud tops are as cold as -85 deg C. The improved structure is translating into stronger surface winds, with the ASCAT passes showing that the initial intensity is now 45 kt. The ASCAT data showed that Fernanda's center is moving south of due west, and the motion estimate is 265/9 kt. Deep-layer ridging to the north of the cyclone is expected to strengthen and build westward, which should keep Fernanda on a west to south-of-due-west trajectory for the next 3 days. The ridge then narrows and weakens a bit on days 4 and 5, which should allow Fernanda to gradually gain some latitude by the end of the forecast period. The recent trend of the track guidance shifting south has continued, and the updated NHC track forecast has therefore been shifted south of the previous forecast during the first 48 hours. After that time, the models are then suggesting that Fernanda's track may take a more pronounced poleward bend, and the new NHC forecast is therefore a little northeast of the previous forecast on days 4 and 5. Northeasterly shear affecting Fernanda has weakened as expected, and it's now analyzed to be about 10 kt. The shear is forecast to diminish further, and it should generally be below 10 kt for the remainder of the forecast period. In addition, Fernanda is currently moving over a warm pool where sea surface temperatures are about 29 deg C. This low-shear, high-SST environment should spark a significant intensification trend in the coming days. HCCA, the Florida State Superensemble (FSSE), and the COAMPS-TC model are all quite aggressive, showing Fernanda becoming a major hurricane just after 48 hours and continuing to strengthen through days 3 and 4. This scenario is supported by the SHIPS RI guidance, which gives a 50/50 chance of Fernanda reaching major hurricane strength in 48 hours. Based on these models, the NHC intensity forecast has been bumped upward, and it generally lies near a blend of HCCA, FSSE, and the ICON intensity consensus. FORECAST POSITIONS AND MAX WINDS INIT 13/0900Z 11.7N 114.1W 45 KT 50 MPH 12H 13/1800Z 11.5N 115.5W 55 KT 65 MPH 24H 14/0600Z 11.2N 117.4W 65 KT 75 MPH 36H 14/1800Z 10.9N 119.3W 80 KT 90 MPH 48H 15/0600Z 10.9N 121.4W 95 KT 110 MPH 72H 16/0600Z 11.6N 125.9W 110 KT 125 MPH 96H 17/0600Z 12.8N 130.2W 115 KT 130 MPH 120H 18/0600Z 14.0N 134.0W 105 KT 120 MPH $$ Forecaster Berg

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Tropical Storm Fernanda Forecast Discussion Number 5

2017-07-13 04:38:35| National Hurricane Center (East Pacific)

Issued at 900 PM MDT Wed Jul 12 2017 000 WTPZ41 KNHC 130238 TCDEP1 Tropical Storm Fernanda Discussion Number 5 NWS National Hurricane Center Miami FL EP062017 900 PM MDT Wed Jul 12 2017 Recent microwave images show that the center of Fernanda remains near the northeastern edge of the deep convection due to light-to- moderate northeasterly shear. However, the center has become a little more embedded within the cold cloud tops this evening. As a result of the slight improvement in organization, the initial wind speed has been increased to 40 kt. The global models show the shear over Fernanda decreasing within the next 12 to 24 h and becoming quite low while the cyclone moves over warm water during the remainder of the forecast period. This should lead to strengthening and most of the intensity guidance brings Fernanda to major hurricane strength in 3 to 4 days. The updated NHC forecast is slightly higher than the previous advisory and also shows Fernanda becoming a major hurricane. It should be noted that the SHIPS Rapid Intensity Index shows a 50 percent chance of a 65 kt increase in intensity over the next 3 days. Fernanda is moving westward to west-southwestward at about 8 kt. A deep layer ridge to the north of the cyclone is forecast to build westward during the next few days which should keep Fernanda on a west or slightly south-of-west heading. After 72 h, the tropical cyclone is forecast to turn west-northwestward as it nears the western portion of the ridge. The track guidance is in good agreement through 72 hours, but there are some differences in the forward speed of the cyclone and how much latitude it will gain later in the period. The NHC track is similar to the previous advisory and lies along the southern edge of the guidance envelope at days 4 and 5. This is in best agreement with the ECMWF and the HFIP corrected consensus models. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 11.9N 113.1W 40 KT 45 MPH 12H 13/1200Z 11.9N 114.5W 50 KT 60 MPH 24H 14/0000Z 11.7N 116.5W 60 KT 70 MPH 36H 14/1200Z 11.5N 118.5W 70 KT 80 MPH 48H 15/0000Z 11.4N 120.6W 80 KT 90 MPH 72H 16/0000Z 11.7N 125.1W 95 KT 110 MPH 96H 17/0000Z 12.5N 129.5W 100 KT 115 MPH 120H 18/0000Z 13.5N 133.5W 100 KT 115 MPH $$ Forecaster Brown

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