How to keep current velocity while jumping?

I'm creating an FPS just as a pet project of mine and I'm having lots of trouble fine-tuning the jumping. I want to be able to jump to where no matter where you turn the camera after you jump, you'll continue moving the way you first looked while jumping, unless i press the movement keys. Most of the code in from the Acacia Developer's character controller video, which doesn't include jumping, I can't think of a way to do it and I haven't found any youtube tutorials that help. Thanks in advance!

Movement script code:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class PlayerController : MonoBehaviour
 {
     [SerializeField] Transform playerCamera;
 
     [SerializeField][Range(0.1f, 10.0f)] float mouseSensitivity = 1.75f;
     //Makes sensitivity Slider bar in inspector
     [SerializeField] float walkSpeed = 5.0f;
     [SerializeField] float airSpeed = 5.0f;
     [SerializeField] float jumpForce = 5.0f;
     bool isJumping = false;
 
     [SerializeField] float gravity = -13.0f;
 
     [SerializeField] float slopeForce;
     [SerializeField] float slopeForceRayLength;
 
     [SerializeField] [Range(0.0f, 0.5f)] float moveSmoothTime = 0.1f;
     [SerializeField] [Range(0.0f, 0.5f)] float mouseSmoothTime = 0.03f;
 
 
     [SerializeField] bool invertedYAxis = false;
     [SerializeField] bool lockCursor = true;
 
 
     float cameraPitch = 0.0f;
     float velocityY = 0.0f;
 
     float tempVelY = 0.0f;
     float tempCurDir = 0.0f;
 
     Vector3 velocity;
 
     CharacterController controller = null;
 
     Vector2 currentDir = Vector2.zero;
     Vector2 currentDirVelocity = Vector2.zero;
     Vector2 currentMouseDelta = Vector2.zero;
     Vector2 currentMouseDeltaVelocity = Vector2.zero;
 
 
     void Start()
     {
         controller = GetComponent<CharacterController>();
 
         if(lockCursor)
         {
             Cursor.lockState = CursorLockMode.Locked;
             Cursor.visible = false;
         }
     }
 
     // Update is called once per frame
     void Update()
     {
 
         updateMouseLook();
         updateMovement();
     }
 
     private void updateMouseLook()
     {
 
         Vector2 targetMouseDelta = new Vector2(Input.GetAxis("Mouse X"), Input.GetAxis("Mouse Y"));
 
         currentMouseDelta = Vector2.SmoothDamp(currentMouseDelta, targetMouseDelta, ref currentMouseDeltaVelocity, mouseSmoothTime);
 
         if (invertedYAxis)
             cameraPitch += currentMouseDelta.y * mouseSensitivity;
         else
             cameraPitch -= currentMouseDelta.y * mouseSensitivity;
 
         cameraPitch = Mathf.Clamp(cameraPitch, -90.0f, 90.0f);
 
         playerCamera.localEulerAngles = Vector3.right * cameraPitch;
         transform.Rotate(Vector3.up * currentMouseDelta.x * mouseSensitivity);
     }
 
     private void updateMovement()
     {
         Vector2 targetDir = new Vector2(Input.GetAxisRaw("Horizontal"), Input.GetAxisRaw("Vertical"));
 
         targetDir.Normalize();
 
         currentDir = Vector2.SmoothDamp(currentDir, targetDir, ref currentDirVelocity, moveSmoothTime);
 
         if (Input.GetButtonDown("Jump") && !isJumping)
         {
             isJumping = true;
             tempVelY = jumpForce;
         }
 
         if (isJumping)
         {
             controller.slopeLimit = 90.0f;
             tempVelY += gravity * Time.deltaTime;
             velocityY = tempVelY;
 
             if (targetDir.y > 0 || targetDir.y < 0)
             tempCurDir = currentDir.y;
 
             if (controller.isGrounded && tempVelY < 0)
             {
                 controller.slopeLimit = 45.0f;
                 isJumping = false;
                 tempCurDir = 0.0f;
             }
         }
         else if (controller.isGrounded && velocityY < 0)
         {
             velocityY = 0.0f;
         }
         else 
             velocityY += gravity * Time.deltaTime;
 
         if (isJumping)
             velocity = (transform.forward * currentDir.y + transform.right * currentDir.x) * airSpeed + Vector3.up * velocityY;
         else
             velocity = (transform.forward * currentDir.y + transform.right * currentDir.x) * walkSpeed + Vector3.up * velocityY;
 
         controller.Move(velocity * Time.deltaTime);
 
         if ((targetDir.x != 0 || targetDir.y != 0) && onSlope())
             controller.Move(Vector3.down * controller.height / 2 * slopeForce * Time.deltaTime);
 
        
     }
 
     private bool onSlope()
     {
         if (isJumping)
             return false;
 
         RaycastHit hit;
 
         if (Physics.Raycast(transform.position, Vector3.down, out hit, controller.height / 2 * slopeForceRayLength))
             if (hit.normal != Vector3.up)
                 return true;
         return false;
     }
 
 }